FM 30-10 ( Terrain Intelligence ) 1967 - Survival ebooks manuals/1967 US Army Vietnam War...CHAPTER...

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DEPARTMENT OF 'THE ARMY FIELD MANUAL

TERRAININTELLIGENCE

IfOPE~}m' OyQUARTERMASTER SCHOOL LUBflAR.U.S. ARMY QUA. TZ. MSIR SCL,

FORT LEE, VA. 22YOlS

,O.ISTx L.at. , : .S,

HEAD QU ARTER S, DEPARTMENT OF T HE ARMYOCTOBER 1967

·_a I i-,IWWW.SURVIVALEBOOKS.COM

I*FM 30-10

FIELD MANUAL

No. 30-10

HEADQUARTERSDEPARTMENT OF THE ARMYWASHINGTON, D.C., 24 October 1967

TERRAIN INTELLIGENCE

INTRODUCTION ..........................--CONCEPTS AND RESPONSIBILITIESNature of terrain intelligence _____.______ .__.Responsibilities -. -------------------PRODUCTION OF TERRAIN INTELLIGENCEIntelligence cycle __ …...__… ____-----__--Sources and agencies ….................... .---WEATHER AND CLIMATEWeather .....................................Climate -..................................Operations in extreme climates _.................NATURAL TERRAIN FEATURESSignificance ..................................Landforms __________ _------------- -------Drainage .............................Nearshore oceanography .................Surface materials ............................Vegetation ...................................MANMADE TERRAIN FEATURESSignificance -..............................Lines of communication …....................Petroleum and natural gas ____. _._______.___Mines, quarries, and pits …....................Airfields -----------------------------Water terminals _______…-------- -----------Hydraulic structures -........................Urban areas and buildings ...................Nonurban areas ___ _---------------------MILITARY ASPECTS OF THE TERRAINMilitary use of terrain _....._________._____._Special operations .........................Water supply ----- --------- ----------TERRAIN STUDIESBasic features _…-------…--------------------Terrain and climate _-___.._____._____..__Military aspects _____- _-------------- ----Coastal hydrography ..........................TRAFFICABILITY -.........................REFERENCES -- ----------------------OUTLINE FOR TERRAIN STUDIES __________SAMPLE TERRAIN STUDY ................SAMPLE CLIMATIC STUDY ______._________NATURAL TERRAIN FEATURES --------------DEPARTMENT OF DEFENSE INTELLIGENCE

INFORMATION REPORT FORMS 1396 AND1396C .................................

1-3

4-78-11

12-1617-23

24-3940-4748-50

51, 5253-6162-6970-7576-8182-91

92, 9394-103

104-108109-112113-115116-118119-121122-128129-131

132-139140, 141142-147

148-153154-156157-166167, 168169-178

INDEX . ................

*This manual supersedes FM 30-I10, 28 October 1959.

1

CHAPTER 1.2.

Section I.II.

CHAPTER 3.Section I.

II.CHAPTER 4.

Section I.II.

III.CHAPTER 5.

Section I.II.

IV.V.

VI.CHAPTER 6.

Section I.II.

III.IV.V.

VI.VII.

VIII.IX.


Ii.III.


II.III.IV.

CHAPTER 9.APPENDIX A.

B.C.D.E.F.

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CHAPTER 1

INTRODUCTION

1. Purpose and Scopea. This manual serves as a guide in the pro-

duction and use of terrain intelligence. Itshows how terrain and weather are evaluatedin military planning and how terrain influ-ences combat. The manual also serves as aguide in understanding the purpose, scope,limitations, and applications of terrain analy-sis. The manual provides information con-cerning the acquisition and use of terrain in-telligence at unit level in a theater of opera-tions.

b. This manual covers basic characteristicsof the natural and manmade features of anarea and their effect on military operations.It defines terrain intelligence and explains theintelligence process of collection, evaluation,interpretation of information, and dissemina-tion of the finished intelligence. It discussessome of the sources of terrain information,including their relative value and use. Guid-ance is furnished for the preparation of theterrain study. The material presented hereinis applicable to both nuclear and nonnuclearwarfare.

2. Changes and CommentsUsers of this manual are encouraged to sub-

mit recommended changes or comments to im-prove it. Comments should be keyed to thespecific page, paragraph, and line of the textin which the change is recommended. Reasonsshould be provided for each comment to insureunderstanding and complete evaluation. Com-ments should be forwarded to the Comman-dant, U.S. Army Engineer School, Fort Belvoir,Va., 22060.

3. Relation to Other ManualsThe material presented in this manual is

related to material in FM 5-30, FM 30-5, andTM 5-545. Other manuals of the FM 30- seriescover specialized intelligence activities. FM100-5, FM 100-15, and FM 101-5 cover intel-ligence in general staff activities and in theplans and operations of large units. Field man-uals of the 5-series contain detailed informa-tion on the operation of engineer troop unitsand their intelligence functions.

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CHAPTER 2

CONCEPTS AND RESPONSIBILITIES

Section I. NATURE OF TERRAIN INTELLIGENCE

4. Definitionsa. Terrain is part of the surface of the

earth, including natural and manmade fea-tures. Both its natural and manmade featuresaffect military operations.

b. Terrain intelligence is processed infor-mation on the military significance of thenatural and manmade characteristics of anarea.

c. Terrain analysis is the process of inter-preting a geographical area to determine theeffect of the natural and manmade features onmilitary operations. It includes the influenceof weather and climate on those features.

d. A terrain study is an analysis and inter-pretation of natural and manmade featuresof an area, their effects on military operations,and the effects of weather and climate on thesefeatures.

e. A terrain estimate is that portion of ananalysis of the area of operations concernedwith the military aspects of the terrain, andthe effects of the characteristics of terrain onenemy and friendly courses of action, includingthe possible use of nuclear weapons.

5. PurposeThe purpose of terrain intelligence is to ob-

tain data about the terrain, weather, and cli-mate, thereby assisting the commander inmaking decisions and the troops in attainingtheir missions. In planning an operation, thecommander and his staff analyze the effectsthat the terrain and weather conditions willhave upon the activities of both friendly andenemy forces. The commander must make themost effective use of the terrain assigned tohis unit. If he is furnished with adequate ter-

rain intelligence, he will be able to exploit theadvantages of the terrain and avoid or mini-mize its unfavorable aspects. By the properutilization of terrain, a numerically inferiorforce may achieve combat superiority over alarger enemy force. The compilation of terrainintelligence is not limited to enemy areas. Italso covers the area occupied by the friendlyforce and also the adjacent terrain.

6. Classificationsa. Mission. Terrain intelligence is classified

according to the mission and level of the com-mand at which it is used. These categories areconsidered broadly as strategic and tactical oroperational. Terrain intelligence is one elementin the intelligence requirements of a com-mander. Engineers have considerable interestin terrain because they are trained and equip-ped to make terrain studies and to conductfield reconnaissance.

b. Strategic. Strategic terrain intelligenceis concerned with large-scale plans and may in-clude the military capabilities of nations. Stra-tegic intelligence is produced continuously andrequires the compilation and interpretation ofinformation by highly specialized personnel.Included in strategic intelligence are descrip-tions and analyses of beaches, water terminals,inland waterways, urban areas, and major ter-rain features; transportation and communica-tion systems; soils, rock types, undergroundinstallations, climate and weather, vegetation,state of ground, and hydrography.

c. Operational. Operational terrain intelli-gence is produced for use in planning and con-ducting tactical or other operations. It is basedupon information secured locally or providedby higher headquarters and is concerned pri-

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marily with the effects of weather and ter- plans, particularly those prepared for specialrain upon the particular operations of the unit.Route reconnaissance reports are of greatestimportance in providing current informationabout routes of communication.

d. Objectives. The difference in the type ofterrain intelligence required by strategic andtactical planners reflects their objectives. Thestrategic planner may consider an entire coun-try or continent, while the tactical planner isconcerned only with the terrain in the areaof his operations. Where the strategic planneroften studies problems that may arise someyears ahead and applies terrain intelligence ina wide variety of hypothetical situations, thetactical planner is primarily engaged withproblems that currently involve his unit, al-though he will study the terrain in his entirearea of possible operation.

7. Applicationsa. Planning. Terrain intelligence is essential

to the commander in order to plan strategicand tactical operations. Detailed and reliableterrain intelligence is required for all logistical

operations or for operations under extremes ofclimate. Special studies, prepared from a logis-tical viewpoint, are essential in planning op-erations in mountains, jungles, or deserts, insnow and extreme cold, and for airborne andamphibious operations.

b. Problems. Research and developmentagencies are concerned with the problems re-sulting from adverse climate, weather, andterrain. Terrain intelligence is necessary todetermine the requirements for new means oftransportation, types of shelter and construc-tion, weapons, and clothing. It is a basic re-quirement in the development of new equip-ment and in the maintenance and modificationof existing equipment.

c. Needs. Current and accurate terrain in-telligence is required by topographic engineeragencies for use in preparing or revising mili-tary maps. Civil Affairs operations depend onaccurate terrain intelligence, particularly con-cerning matters of economic and political im-pact on tactics and logistics.

Section II. RESPONSIBILITIES

8. Department of Defensea. Defense Intelligence Agency (DIA). The

Defense Intelligence Agency (DIA) is anagency of the Department of Defense (DOD)and under the direction, authority, and con-trol of the Secretary of Defense. It is admin-istered by a director, a deputy director and achief of staff at the headquarters which hassuch subordinate units, facilities, and activi-ties as are specifically assigned to the Agencyby the Secretary of Defense or by the JointChiefs of Staff acting under the authority anddirection of the Secretary of Defense. DIA isresponsible for-

(1) The organization, direction, manage-ment, and control of all DOD intelli-gence resources assigned to or in-cluded within DIA.

(2) Review and coordination of thoseDOD intelligence functions retainedby or assigned to the military de-partments. Overall guidance for theconduct and management of such

functions is subject to review, ap-proval, and promulgation by theSecretary of Defense.

(3) Obtaining the maximum economyand efficiency in the allocation andmanagement of DOD intelligence re-sources. This includes analysis ofthose DOD intelligence activities andfacilities which can be fully inte-grated or collocated with non-DODintelligence organizations.

(4) Responding directly to priority re-quests levied upon the DIA by theUnited States Intelligence Board(USIB) and satisfying the intelli-gence requirements of the majorcomponents of the DOD.

b. Assistant Chief of Staff for Intelligence(ACSI). The Under Secretary of the Army isthe DA's responsible officer for its intelligence,counterintelligence, and communications se-curity in international affairs. The intelligenceand counterintelligence activities of the United

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States Army are the responsibility of the As- assigned to a unit formed for that sole func-sistant Chief of Staff for Intelligence (ACSI).His duties include directing the Army mappingand geodesy program and the military geo-graphic intelligence program. He also has theresponsibility for coordinating those activitieswith Army components of unified and speci-fied commands.

c. Chief of Engineers. Under the programdirection of the Assistant Chief of Staff forIntelligence, the Chief of Engineers is re-sponsible for-

(1) Providing direct support to the As-sistant Chief of Staff for Intelligencein mapping and geodesy activities.

(2) Providing technical supervision andcoordination of worldwide geographicintelligence activities.

(3) Providing and directing assigned ele-ments engaged in mapping, geodesy,military intelligence, and related serv-ices, to include maintenance of theDepartment of Defense (DOD) mas-ter worldwide mapping and geodesylibrary and the DOD World GeodeticSystem.

9. CommandCommanders at all levels are responsible for

the production of intelligence, including ter-rain intelligence. A commander must insurethat he and his staff are aware of the effectsof weather and terrain on their mission. Hemust know and utilize the capabilities for pro-ducing terrain intelligence that exist withinhis command or in outside agencies and insurethat his command gathers pertinent informa-tion on the weather and terrain, and transmitsthis to all units requiring it. To do this prop-erly, his command must be trained in the basicskills of terrain analysis. At theater level ter-rain intelligence is more detailed than the in-telligence compiled at national level, and theproduction of theater intelligence may be

tion. At field army and lower levels, combatterrain intelligence is the principal concern,becoming increasingly detailed and localized atsuccessively subordinate levels.

10. Intelligence OfficerThe terrain intelligence that a commander

needs to make a sound decision and an effectiveplan must be provided by the unit intelligenceofficer. As a part of his intelligence report, theintelligence officer makes an analysis of thearea of operations normally based upon a ter-rain study. The intelligence officer must planand coordinate the collection of terrain infor-mation and the production, maintenance, anddissemination of terrain intelligence. Concur-rently, he should keep the officer responsiblefor the preparation of terrain studies informedof the planning that is in progress or in pros-pect, so that the required terrain informationmay be secured and compiled.

11. EngineerUnder the general staff supervision of G2

the staff engineer, or the senior engineer com-mander in the event a staff engineer is notauthorized, carries out the terrain intelligencefunctions. He produces and maintains terrainstudies based upon terrain analyses. This in-volves-

a. Determining the requirements for terraininformation, based upon requests from G2.

b. Collecting and evaluating terrain infor-mation.

c. Assembling terrain intelligence into aterrain study. He provides technical interpre-tation of the terrain covering such factors ofmilitary significance as obstacles, routes, andavenues of approach, cover and concealment,landforms, hydrology, crosscountry movement,and related subjects. He also disseminates ter-rain studies and technically evaluated infor-mation.

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CHAPTER 3

PRODUCTION OF TERRAIN INTELLIGENCE

Section I. INTELLIGENCE CYCLE

12. PhasesThe intelligence cycle described in FM 30-5

is also followed in the production of terrainintelligence. The activities associated with in-telligence operations follow a four-step cycle,oriented on the commander's mission. The foursteps are-

a. Planning the collection effort and pre-paring orders.

b. Collecting the information.c. Processing the collected information.d. Disseminating and using the resulting in-

telligence.

13. The Collection Efforta. Direction. Terrain intelligence is directed

by the responsible intelligence officer in thename of the commander. This direction in-volves-

(1) Determination of intelligence require-ments.

(2) Preparation of a collection plan.(3) Issuance of orders and requests to ap-

propriate collection agencies.(4) Continuous check on the production

activities of the collection agencies.b. Steps. Five successive steps are involved

in direction-(1) Determination of the information re-

quirements.(2) Analysis of the requirements to de-

termine indications that would an-swer the questions presented.

(3) Translation of these indications intoorders and requests for informationpertaining to specific activities, local-ities, characteristics, or conditions.

(4) Selection of collection agencies to be

employed and issuance of the neces-sary orders and requests.

(5) Followup.

14. CollectingCollecting is the systematic exploitation of

sources of information and the reporting ofthe information thus obtained to the properintelligence agencies. A source is the person,thing, or activity from which information isobtained. An agency is any individual or orga-nization which collects or processes informa-tion. Sources of terrain information and collec-tion agencies are discussed in paragraphs17 through 23.

15. Processing Sequencea. Processing is the step in the intelligence

cycle whereby information becomes intelli-gence.

b. Recording involves the reduction of in-formation to writing or other graphical formof presentation and the grouping of relateditems to facilitate study and comparison.

c. Evaluation is the appraisal of an item ofinformation to determine its pertinence, thereliability of the source or agency, and theaccuracy of the information.

d. Interpretation is the result of criticaljudgment involving analysis, integration, anddeduction. Analysis is the sifting and sortingof evaluated information to isolate significantelements with respect to the mission and op-erations. Integration is the combination of theelements isolated in analysis with other knowninformation to form a logical picture of enemyactivities or the influence of the characteristicsof the area on the mission of the command.Deduction is the acquisition of a meaning from

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the hypothesis developed, tested, and consid- photointerpretation reports, and climatic sum-ered valid.

16. Dissemination and UseTerrain intelligence is disseminated to com-

manders and staffs as one element of the over-all intelligence report. Dissemination may beaccomplished by means of briefings, confer-ences, messages, or such intelligence documentsas the estimate, summary, periodic report, ananalysis of area of operations, annex, maps,

maries. The information and intelligence areinstruments in detecting enemy targets anddeveloping-effective combat power. The meansand methods selected for dissemination dependupon the 'detail, pertinence, and urgency of theinformation and intelligence as well as its in-tended use. Consideration is given to the needsof the user, his resources for using the mate-rial, and the capabilities of available commu-nications.

Section II. SOURCES AND AGENCIES

17. Maps and Terrain Modelsa. Maps. Maps are a basic source of terrain

information. They are intelligence documents,not supply items. Accordingly, the intelligenceofficer usually is responsible for staff super-vision over military maps and survey activities.The classification of US maps by type andscale is explained in AR 117-5. Foreign maps,or those copied from maps that were preparedby foreign agencies, often vary from US stand-ards and procedures. Reliability informationis indicated in the margin of US producedtopographic maps. Foreign maps may notprovide this. Portions of one map sheet maybe fully reliable and yet other parts of thesame sheet may be based on obsolete data. Theuse of a map must be regulated by an estimateof the probable changes in manmade featuresthat have occurred since the date of the latestrevision. All personnel must be impressed withthe importance of reporting errors, changes,and omissions in existing maps, so that neweditions may incorporate the necessary correc-tions. Maps prepared for a special purpose maynot be reliable for information that is not re-lated to that purpose. A railway map, for ex-ample, may be quite accurate in presentingrailway information, but may be unreliablefor data shown on roads or other features.Special maps and overlays may be preparedfor a specific military purpose or to show onlyparticular characteristics of the terrain.

(1) Soil maps are prepared primarily foragricultural purposes to show the po-tentialities of the soil for crop pro-duction. This type of map shows soilsof various types, indicating their de-

gree of acidity, nutrients, suitabil-ity for certain crops, and similar in-formation. Engineering soil mapsindicate the qualities of soil construc-tion or vehicle movement. Agricul-tural soil maps may be used for en-gineering purposes after they havebeen interpreted according to engi-neering nomenclature and require-ments.

(2) Geologic sketch maps indicate thegeology of an area. Outcrop mapsshow the bedrock that is exposed.Bedrock maps show the surface ofthe bedrock as it would appear if theoverlying soils were removed. Thesemaps are useful in locating sites formajor structures and in findingsources of rock for construction pur-poses when the overburden has beendescribed.

(3) Communication maps include thosethat show the system of lines andsequence of stations of railways, pro-vide automobile route information,and indicate navigable waterwaysand the routes and stops of airlines.These really could be consideredtransportation maps.

(4) Relief maps show differences in eleva-tion by the use of various tints andshading patterns. A plastic relief mapis a standard topographic map printedon a plastic and molded into a three-dimensional form with a 2:1 exag-geration in the relief. Because of theshrinkage characteristics inherent in

8


plastic materials, there is considerabledistortion of the features shown onthis type of map. For example, somestream lines may appear not coin-cident with valley bottoms:

(5) Pictomaps are maps on which thephotographic imagery of a standardphotomosaic has been converted intointerpretable colors and symbols. Des-ert sands, swamps, jungle, glaciers,and extra terrestrial topography aresome of the features that are ideallyportrayed on a pictomap. Shadows ofmap features are emphasized on thepictomap. They accurately delineatemany cultural features, and they lenda three-dimensional effect to buildingsand vegetation. This effect symbolizesand establishes relative heights ofthese cultural features. The pictomapis an excellent source for terrain in-formation.

(6) Other special maps show the distri-bution of major vegetation types andshow depth of depressions for use inmountain and winter operations; wa-ter supply sources and distributionsystems; structure of town and cityplans; conditions affecting cross-country movement; and similar de-tailed information that can be pre-sented most effectively in graphicform.

b. Terrain Models. A terrain model is athree-dimensional graphic representation of anarea showing the conformation of the groundto scale. Usually it is colored to emphasizevarious physical features, and the verticalscale is exaggerated to convey relief. Terrainmodels may be made for use in strategic ortactical planning, assault landings, airbornelandings, and aerial target delineation.

18. Photographs and Remote-SensorImagery

a. General Features. Aerial and groundphotographs provide an accurate visual recordof the terrain. They furnish information thatis not readily available or immediately ap-parent by ground reconnaissance or by visualobservation from the air, especially of enemy-held areas.

Photographs preserve information in a per-manent form, so that it is available for laterstudy and comparison. Remote-sensor imageryincludes infrared photography and side-lookingairborne radar. It provides imagery recordsof terrain, vegetation, and cultural featuresthat may be obscured by atmospheric, natural,or artificial cover.

b. Advantages. Properly interpreted, aerialand ground photography and airborne infrar-ed and radar imagery will furnish detailedinformation concerning:

(1) The identification of vegetation soilsand rocks.

(2) Both surface and subsurface drainagecharacteristics. Indications of surfacedrainage can be located, marked, andevaluated through detailed stereostudy. In some cases, subsurfacedrainage can be predicted in generalterms, such as, "well-drained" or"poorly drained."

(3) Suitability of terrain for construc-tion of airfields, roads, and under-ground installations, based upon topo-graphy, drainage, soils, and engineer-ing materials. General character-istics can be given, such as"flat plain,predominantly fine-grained soils, well-drained, forest cover, deposits ofgravel suitable for borrow."

(4) Suitability of terrain for cross-coun-try movement and airborne and air-mobile operations. Photographs andphotomaps can be used advantageous-ly in studying and rating areas asto their suitability for movement,based on the evaluation of relief,slopes, drainage, soils, and vegeta-tion. General characteristics may bedetermined, such as "flat plain, grass-covered, silty soils, hedgerows, poordrainage."

(5) Aerial and ground photographs, in-terpreted by skilled personnel, cangive highly detailed informationabout all types of manmade features,from artificial obstacles to largeindustrial complexes.

(6) Photographs depict up-to-date terrainfeatures. Maps depict only what the

9


mapmaker saw at the time the map-ping information was gathered.

c. Limitations. The amount of informationthat can be derived from interpretation ofphotography is limited by adverse weatherand by densely forested terrain. Aerial photo-graphs may not provide detailed factual in-formation concerning the engineering prop-erties of soil, vehicle type and trafficabilityrelationships, and quantitative data for mate-rials and other items. This type of informationusually can be obtained only through fieldsampling and laboratory testing proceduresor by comparison with information from recon-naissance reports, geological surveys, andsimilar sources. It is important that informa-tion obtained from aerial and ground photo-graphs should be correlated with informationfrom other sources, such as maps, personalreconnaissance, and reports from intelligenceagencies.

d. Requirements. There should be sufficientaerial photograph coverage made to enable theinterpreter to determine the extent of localconditions and the expected variations. Usuallyvertical coverage is best for measurements, al-though oblique photographs are more usefulfor certain purposes, such as in the study ofdense forest areas. Scales of 1:5,000 to 1:20,-000 are desirable for detailed terrain analysis.Photographs in this range provide good areacoverage and stereoscopic perception of re-lief. They show such details as major gullycharacteristics, and the outstanding terrainfeatures.

(1) Photographs with scales smaller than1:30,000 provide excellent area cover-age in the broadest sense. Majorphysiographic details are easily seenand studied; relief must be great,however, before stereovision is prac-ticable because only major reliefforms are clearly differentiated atthese scales, and small details are lost.Major gullies can be plotted, for ex-ample, but in some cases their char-acteristics cannot be determined. Asa rule, landforms can be delineatedonly when there is a great contrast inpattern. Slopes associated with land-forms at times cannot be seen or

distinguished. While such manmadefeatures as roads, railroads, bridges,and buildings can be identified, theinterpreter may have difficulty indetermining their structural details.Colored film is frequently the mosteffective for identifying vegetation.The best' scale depends on the dataneeded. Vegetation can also be iden-tified from differences in tone onblack and white aerial photographs.

(2) Stereopairs, vectographs, and an-aglyphs are particularly useful inmaking terrain studies. A stereopairconsists of two photographs of thesame terrain taken from differentpositions. Usually they are takenfrom a position vertically above thearea being photographed with about60 percent of each photo (called theoverlap) common to both photo-graphs. Examination with a stereo-scope gives an exaggerated third-di-mensional view of the terrain includ-ed in the overlap. A vectograph is aprint or transparency in which thetwo photographs of the stereoscopicpair are rendered in terms of degreeof polarization presenting a stereo-scopic image when viewed throughPolaroid spectacles. An anaglyph is apicture combining two images of thesame object, recorded from differentpoints of view, as images of the rightand left eye, one image in one colorbeing superimposed upon the secondimage in a contrasting color. Viewedthrough a pair of light filters, the an-aglyph produces a stereoscopic effect.

(3) Controlled mosaics of an area providean accurate map from which measure-ments of distances can be obtained.The amount of detail useful for ter-rain analysis will depend upon thescale of the mosaic.

19. Books and PeriodicalsValuable terrain information can be found

in a wide variety of books and periodicals.These include trade journals, economic atlases,tide tables, pilots' handbooks, tourist guides,and similar publications. Unpublished syste-

10


matic records covering meteorological, hydro-logical, and similar scientific data preparedby government agencies, engineering firms,private societies, and individuals also contrib-ute valuable terrain information. Althoughutilized chiefly for terrain studies made byhigher headquarters, material of this type,when locally available, can be of considerablevalue to lower echelons.

20. Intelligence ReportsStrategic intelligence studies prepared by

Department of Defense agencies provide de-tailed terrain information concerning majorgeographical areas. Such studies include-

a. National Intelligence Survey (NIS). Thisis a series of documents covering the coun-tries of the world, presenting a digest of thebasic intelligence required for strategic plan-ning and for the operations of major units.Each survey describes in detail the terraincharacteristics of a specific area or nation sup-ported by descriptive material, maps, charts,tables, and with reliability ratings assigned toall data.

b. Engineer Intelligence Studies (EIS).These are no longer published, but the EISfiles are still an important source. These docu-ments describe in detail those natural andmanmade features of an area that affect thecapabilities of military forces, particularlywith reference to engineer operations. Theywere produced by the Office, Chief of Engineers.

c. Lines of Communication (LOC). Thesestudies, prepared on either medium scale mapsor single, small-scale foldup sheets, contain ananalysis of transportation facilities with in-formation on railroads, inland waterways, high-ways, airfields, pipelines, ports, and beaches.

d. Terrain Studies. These contain area in-telligence depicted on medium and small scalemaps with accompanying textual and graphicmaterial. They are for strategic planning, anddescribe principal terrain characteristics,major aspects of land, water and air move-ment, and key installations.

e. Special Reports on Military Geography.These are designed primarily for strategicplanning and generally directed towards anal-ysis of a major aspect of military geographysuch as cross-country movement, amphibious

operations, and airborne operations.f. Engineer Reconnaissance Reports. Re-

ports that summarize data obtained by re-connaissance are a major source of terrain in-formation. They are of particular value inproviding current, detailed information aboutlines of communication and availability ofnatural construction materials.

21. Captured Enemy DocumentsMaps and other intelligence documents

captured from the enemy often are of greatvalue as sources of terrain information. Usu-ally, enemy-prepared military maps and ter-rain studies of enemy territory will be more upto date and detailed than our own. The proc-essing of captured enemy documents is de-scribed in FM 30-15.

22. InterrogationInterrogation personnel should be kept in-

formed of the terrain information that is re-quired by intelligence officers. Useful infor-mation about the area held by enemy forcesfrequently can be obtained from prisoners ofwar, deserters, liberated civilians, refugees,escapees, evadees, cooperative enemy nationals,and self-surrendered and apprehended enemyespionage agents.

23. Collection Agenciesa. Units. Collection agencies include intel-

ligence personnel, troop units, and special in-formation services. FM 30-5 discusses thetypes and capabilities of these agencies. Allunits within a command may be employed bythe intelligence officer to secure terrain infor-mation. In addition, he may request higherheadquarters to use their units and facilities tosecure information he requires.

b. Troops. Reconnaissance missions to secureterrain information may be assigned to combator combat support units. Such missions maybe accomplished by units specifically organiz-ed for reconnaissance or by other units as-signed reconnaissance missions in addition totheir normal activities.

c. Aircraft. In addition to ground recon-naissance, aircraft may be employed to secureinformation about the terrain. Although itmay be limited by adverse weather or enemyair defense, air reconnaissance is the fastest

11


means of gathering terrain information and, natural earth sciences who prepare special ter-at times, may be the most practical meansof reconnoitering enemy territory. Informa-tion on objects such as trees, structures, andcommunication lines is of great importance forairmobile and air landing operations. Armyaviation has the capability to conduct airreconnaissance missions, but additional sup-port may be requested through intelligencechannels for reconnaissance flights to be ac-complished by the Air Force.

d. Specialized Agencies. An engineer ter-rain detachment usually is assigned to eachcorps. The detachment is composed of person-nel in various fields of engineering and the

rain studies, evaluate all types of terrain in-formation, and serve as consultants to agenciesfaced with technical problems. Terrain infor-mation may be provided by personnel whosenormal duties are not primarily concerned withterrain intelligence. These include militaryintelligence personnel of the MI battalion, fieldarmy, and MI detachments at corps. CivilAffairs staffs acquire terrain intelligence inconsiderable detail, particularly in the areas ofagriculture, forestry and fishing, transporta-tion, and other economic functions. CivilAffairs area studies and surveys are sources ofinformation and intelligence.

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CHAPTER 4

WEATHER AND CLIMATE

Section I. WEATHER

24. DefinitionWeather comprises the day-to-day changes

in atmospheric conditions. The physical prop-erties and conditions of the atmosphere thatmust be measured or observed to describe thestate of the weather are termed the weatherelements.

25. Air Temperaturea. Measuring. Air temperature is the degree

of hotness or coldness of freely circulating airas measured by a thermometer that is shield-ed from the sun. The thermometer is cali-brated by using the melting point of ice andthe boiling point of water at sea level as

C = 5 (F - 32° )

F = - X 0 C +3205

b. Recording. Temperature data may be re-corded in the following forms:

(1) Mean daily maximum temperature.The average of the daily maximumtemperatures for a month.

(2) Mean daily minimum temperature.The average of the daily minimumtemperatures for a month.

(3) Mean daily temperature. Average ofdaily maximum and minimum tem-peratures for any specific day.

(4) Mean monthly temperature. Averageof daily mean temperatures for anyspecific month.

(5) Mean annual temperature. Averageof daily mean temperatures for any

standard references. In most English-speakingcountries, the Fahrenheit scale is used, withthe melting point of ice designated as 32°Fabove zero and the boiling point of water as212°F above zero. Countries using the metricsystem employ the centigrade (Celsius) scale,with the freezing point of water designatedas 0° C and the boiling point, 1000 C. In theUnited States, surface air temperatures areindicated in degrees Fahrenheit and upperair temperatures in degrees centigrade. Tem-peratures may be converted from one of thesescales to the other by use of the followingformulas:

Example: Change 770 F to C.

Multiply 770 F - 320 by A, which9equals 2equals 250 C.

Example: Change 250 C to F.

Multiply 250 C by- - and add 320,5

which equals 770 F.

specific year.(6) Mean annual range. Difference be-

tween the mean monthly tempera-tures of the warmest and coldestmonths.

(7) Diurnal variation. Difference be-tween the maximum and minimumtemperatures occurring in a day.

(8) Normal values, or long-term mean.The average of temperature values forthe entire period of record. Thesevalues usually are used to evaluatethe climate.

(9) Extreme values. Absolute maximumor absolute minimum or extremevalues.

13


(10) Length of freezing period. Number cate low-pressure areas and those significantlyof days with minimum temperaturebelow freezing.

c. Use of Data. Monthly daily maximum andmean daily minimum temperatures usually areemployed to provide a general definition of thetype of climate, and the mean annual rangeto indicate its variability. Extreme values showthe limits which must be anticipated in theclimate being considered. Temperatures alsoare recorded at various altitudes above theground level in order to provide data for esti-mating certain types of nuclear-weapon effects.

26. Atmospheric Pressurea. Definition. Atmospheric pressure is the

force exerted per unit of area by the weightof the atmosphere from the level of measure-ment to the top of the atmosphere. At sealevel this pressure is approximately 6.66 kilo-grams per 6.45 square centimeter or 14.7pounds per square inch. Mean sea level is usedas a reference for surface weather observa-tions, and pressure measurements are shownon weather maps and climatic charts as if theentire surface of the earth were at sea level.Atmospheric pressures are recorded at variousaltitudes to provide data for estimating nu-clear-weapon effects.

b. Measurement. The standard device formeasuring atmospheric pressure is a mercurialbarometer which balances the weight of theatmosphere with a column of mercury. Thestandard atmospheric sea-level pressure isequal to that exerted by a 760 millimeter(29.29 inch) column of mercury at 320 F. andat standard gravity. For some scientificpurposes, it is desirable to indicate atmosphericpressure in units of pressure (weight per unitof area) rather than in units of length(centi-meters or inches). In the metric systems, a baris the unit of measure. The millibar (1/1000of a bar) is used in meteorology to designatethe value of atmospheric pressure. Thestandard sea level pressure is 1013.2 millibars.One millibar equals .0762 centimeters or 0.03inches of mercury. Most weather stations to-day observe pressure on an aneroid barometer,calibrated in both millibars or inches or milli-meters of mercury. Barometer readings sig-nificantly below 760 millimeters usually indi-

above 760 millimeters usually indicate high-pressure areas. In general, cold air, beingheavy and.dense, causes high barometric pres-sures, while hot air, which is light and thin,causes low pressures. High-pressure systemsusually are associated with fair, dry weather;low-pressure systems, with unsettled, cloudyconditions.

27. Windsa. Description. Wind is air in motion and

results from differences in atmospheric pres-sure. A wind is described by its direction andspeed. The direction of a wind is the directionfrom which it is blowing. A wind comingfrom the north, for example is termed a northwind. As reported in observations, winddirection is determined with reference to truenorth and is expressed to the nearest 10degrees. Thus, a direction of 090 degrees (awind from due east) would be reported as 09.Wind velocities are reported by the AirWeather Service in knots. A table of windspeeds and their specifications is given (table1) to aid in estimating speeds. Over ir-regular terrain, a wind does not move with asteady force or direction, but as a successionof gusts and lulls of variable speed anddirection. These eddy currents, caused byfriction between air and terrain, are calledgusts or turbulence. Turbulence also resultsfrom unequal heating of the earth's surface,the cooler air of adjacent areas rushing in toreplace the rising warm air from heated areas.Usually the turbulence produced by surfacefriction is intensified on a sunny afternoon.

b. Systems. Local pressure and wind systemsare created by valleys, mountains, and landmasses that change the weather characteristicsof areas. Since land masses absorb and radiateheat more rapidly than water masses, the landis heated more than the sea during the dayand cools more at night. In coastal areas,warm air over the land rises to a higheraltitude and then moves horizontally out tosea. To replace this warm air, the colder airover the water moves on to the land, creatingthe so-called sea breeze. The circulation isreversed at night, so that the surface air movesfrom the land to the sea, resulting in a landbreeze.

14


Table 1. Weather Map Scale of Wind Velocity

Descriptiveitenm Knots Metersfleconds Specifications

Calm -.............Light air ..........

Light breeze --------Gentle breeze --------

Moderate breeze …---

Fresh breeze --------

Strong breeze …_-----

Near gale _________

Gale _-___-_._._._- _

Strong gale ________.

Storm -------------

Violent storm _______.

Hurricane _________

less than1-3

4-67-10

11-16

17-21

22-27

1

28-33

34-40

41-47

48-55

56-63

64 and over

0-0.20.3-1.5

1.6-3.33.4-5.4

5.5-7.9

8.0-10.7

10.8-13.8

13.9-17.1

17.2-20.7

20.8-24.4

24.5-28.4

28.5-32.6

32.7 and over

Calm; smoke rises vertically.

Direction of wind shown by smoke drift butnot by wind vanes.

Wind felt on face; leaves rustle.

Leaves and small twigs in constant motion;wind extends light flag.

Raises dust and loose paper; small branchesare moved.

Small trees in leaf begin to sway; crestedwavelets form on inland waters.

Large branches in motion; whistling heard intelegraph wires; umbrellas used with diffi-culty.

Whole trees in motion; inconvenience felt whenwalking against wind.

Breaks twigs off trees; generally impedesprogress.

Slight structural damage occurs (chimneypots, slates and shingles removed).

Seldom experienced inland; trees uprooted;considerable structural damage occurs.

Very rarely experienced; accompanied bywidespread damage.

S DCN RM

Figure 1. Chinook or foehn effect.

15

bblawpppw�


c. Vally Wind. Heated by the daytime sun, cept where the monsoon winds pick upthe air in contact with a mountain slope be-comes lighter than the surrounding air andrises up the slope, being replaced by denser,colder air. This air movement is called a valleywind because it appears to be flowing up fromthe valley. At night the air in contact withthe slope becomes colder and more dense, sink-ing down along the slope to create a mountainbreeze that seems to flow out of the mountain.Mountain breezes generally are stronger thanvalley winds, especially in the winter.

d. Chinook. A chinook (North America) orfoehn (Europe) (fig. 1) is a phenomenonthat occurs in winter and spring on the leeor downwind side of mountain ranges overwhich there flows a steady crosswind ofmoisture-laden air. As the air rises over thewindward side of the mountains it expands andcools rapidly, producing clouds and precipita-tion. As the air moves down the lee side of themountain range it compresses and warms. Asa result, there are warm, dry winds on the leeside of the mountains.

e. Fall and Gravity. Fall and gravity windsare caused by the descent of downslope airthrough the action of gravity. They are typ-ical of the Greenland coast, which is essen-tially a high plateau sloping abruptly to thesea along an irregular coastline cut by manyfiords. The central plateau area remains ice-covered throughout the year, developing ex-tremely cold air masses which frequentlydrain off through the fiords to the sea andattain a near-hurricane speed. At sea level thewinds remain relatively cold and very dry.Similar winds are the bora, which drain offthe southern Alps and the Balkan Plateauinto the Adriatic Sea, and the mistral of theRhone Valley in France.

f. Monsoon. A monsoon wind is any season-ally changing or reversing wind. It is strongestand steadiest on the southern and easternsides of Asia. It blows outward from high-pressure centers overland toward the sea inwinter and inward toward low-pressure over-land in summer. In most regions, the summermonsoon season is generally characterized byextensive cloudiness and frequent precipita-tion. The winter monsoon season is character-ized by dry air and infrequent cloudiness ex-

moisture by moving over warm seas beforestriking an island or peninsular coastline.

28. Humiditya.' Vapor.'Water vapor is the most important

constituent of the atmosphere that determinesweather phenomena. Although the oceans arethe primary source, a limited amount of watervapor also is furnished to the atmospherefrom lakes and rivers, snow, ice fields, andvegetation. The percentage of water vapor byvolume in the air may vary from practicallyzero in deserts to 4 or 5 percent in humidtropical areas.

b. Amount. Humidity is the term used todescribe the amount of water vapor in the air.The amount that the air actually containscompared with what it could hold at a giventemperature and pressure is termed the rela-tive humidity. When a specific air mass holdsall the moisture that it can at a given temper-ature, it is described as having a relativehumidity of 100 percent.

c. Dew Point. The dew point is that temper-ature at which the air becomes saturated. Thehigher the dew point, the greater amount ofwater vapor the air can hold. The closer thedew point temperature is to the actual temper-ature, the greater the likelihood of condensa-tion. Condensation results when the capacityof the atmosphere to hold water is reduced bycooling, so that the water vapor in the air ischanged to visible moisture such as fog orclouds.

29. Cloudsa. Classification. Clouds are masses of con-

densed moisture suspended in air in the formof minute water droplets. They are classifiedaccording to their form or appearance and bythe physical processes producing them. TheAir Weather Service reports the type of cloudspresent, the heights of the cloud bases andcloud tops, the amount of cloudiness, and thedirection in which the clouds are moving. Cloudamounts are reported in terms of the fractionof the sky that is covered by clouds (fig. 2).The following terms are used:

(1) Clear. No clouds, or less than 0.1 ofthe sky covered.

16


Figure 2. Cloud cover symbols.

(2) Scattered. 0.1 to 0.5 of the sky cov-ered.

(3) Broken. 0.6 to 0.9 of the sky covered.(4) Overcast. More than 0.9 of the sky

covered.b. Heights. Cloud heights are reported in

meters above the ground. The heights ofclouds below 1,500 meters (5,000 feet) are re-ported to the nearest 30 meters (100 feet);clouds from 1,500 to 3,000 meters (5,000 to10,000 feet) are reported to the nearest 150meters (500 feet), and clouds above 3,000meters (10,000 feet) to the nearest 300 meters(1,000 feet). A ceiling is defined as the lowestlayer of clouds that is reported as broken orovercast and not classified as thin. Heights ofclouds are reported in meters or feet above thepoint of observation.

c. Direction. Cloud direction is the directiontoward which the cloud bases are moving. It isreported according to the eight points of thecompass.

d. Appearance. According to their appear-ance, clouds are either cumiliform or strati-form. Cumiliform clouds are formed by risingcurrents in unstable air. Stratiform clouds re-sult from the cooling of air in stable layers.

(1) Cumiliform clouds are dense withvertical development. The upper sur-face of a cumiliform cloud is dome-shaped, while the base is nearlyhorizontal. Usually clouds of this type

are separate from each other andrarely cover the entire sky. The pre-cipitation from cumiliform cloudsgenerally is showery in nature.

(2) Stratiform clouds usually occur inlayers that may extend from horizonto horizon, without the vertical de-velopment of cumiliform clouds. Pre-cipitation from this type of cloudusually is in the form of light con-tinuous rain, drizzle, or snow.

e. Groupings. Clouds may be grouped intofour families (fig. 3)-

(1) High. Cirrus, cirrostratus, cirrocumu-lus.

(2) Middle. Altostratus, altocumulus.(3) Low. Stratus, nimbostratus, strato-

cumulus.(4) Vertical development. Cumulonimbus

for an example.f. High Clouds. High clouds usually occur at

heights of from 6,000 to 12,000 meters (20,-000 to 40,000 feet), although they may befound at much lower altitudes in polar regions.They are composed of ice crystals. The charac-teristics of the major cloud types in this groupare as follows:

(1) Cirrus. This is a delicate white fibrouscloud that often appears bright yel-low or red from the reflection of lightfrom a rising or setting sun. Cirrus

17

0 () 20 3 4

two orno clouds one-tenth three-tenths four- tenths five-tenths


8,000M -

25,000 FT -

7,000 M -

20,000 FT. -

6,00 M -

5,000 M -

15,000 FT -

4,000 M -

10,000 FT-3,000 M -

2pOOM -

%000 FT.-

1,000 M -

0-

Kj

dltocumulus 'z-s

--V - ~- S :- . I . .- .

I ,, - or .

.1 : ; 1.I -1

altostratus

Figure S. Major cloud types.

18

.. iUS I

I~:~

I'I:-"71A-.'::, \

i .~~~~~i. z 7s

'I

I -

.·n a e~sa


clouds may appear as isolated tufts,featherlike plumes, or streaks withupturned ends often referred to asmare's tails. Because of. their thin-ness, cirrus clouds do not blur theoutlines of the sun or moon, and usu-ally do not make an appreciablechange in the appearance of the sky.

(2) Cirrostratus. These are thin, whitishveils of clouds that give the sky amilky look. Usually they can be dis-tinguished from cirrus clouds by thehalo which light from the sun ormoon produces in them.

(3) Cirrocumulus. Clouds of this typeconsist of patches of small, roundedmasses or white flakes arranged ingroups or lines.

g. Middle Clouds. Middle clouds usually occurat altitudes of 1,800 to 6,000 (6,000 to 20,000feet) meters in the lower limit of this rangein the colder seasons, and at altitudes near theupper limit in the warmer seasons. The majortypes are-

(1) Altostratus. Clouds of this type ap-pear as a veil of gray or bluish fibrousclouds, the thinner forms resemblingthe thicker forms of cirrostratus.Altostratus clouds are associated withsmooth or stable air layers, and occa-sionally they produce light rain orsnow.

(2) Altocumulus. This cloud type can ap-pear as a layer or in patches, is whiteor gray in color, and the cloud ele-ments appear as rounded masses orrolls. They occur in a variety offorms, and may exist at several levelsat the same time.

h. Low Clouds. Low clouds usually havebases below 1,800 meters (6,000 feet) and in-clude the following types:

(1) Stratus. These form a low layer re-sembling fog, although they do notrest upon the surface. They give thesky a hazy appearance. The base ofthis cloud is usually rather uniformin height but it often occurs in theform of ragged patches or cloud frag-ments. Layers of stratus clouds maycover hundreds of thousands of

square miles. Usually they are thin,and range in thickness from a fewhundred feet to several thousand feet.Frequently, stratus clouds are accom-panied by fog, haze, or smoke be-tween their bases and the ground.Visibility is very poor under stratusclouds, and precipitation from themusually is in the form of light snow ordrizzle.

(2) Nimbostratus. Clouds of this typeform a low, dark gray layer. Precipi-tation usually is in the form of con-tinuous rain or snow of variableintensity. Because of its thickness,sometimes more than 4,500 meters(15,000 feet), the nimbostratus is fre-quently classified as a cloud of verti-cal development.

(3) Stratocumulus. This type of cloudforms a lower layer of patches ofrounded masses or rolls. The base ofthe stratocumulus usually is higherand rougher than the stratus clouds.Frequently these clouds change intothe stratus type.

i. Vertical. Vertical development clouds can-not be classified according to height, sincethey extend through all the levels assigned toother cloud groups. The bases vary from 150to 3,000 meters (500 feet to 10,000 feet) orhigher, while the tops may vary from 450meters (1,500 feet) to more than 12,000 meters(40,000 feet). They all occur in relatively un-stable air and frequently are associated withstrong vertical currents and intense turbu-lence. In this category are the following:

(1) Cumulus. Clouds of the cumulus typeare dense, with vertical development.The base is horizontal and uniformin height above the earth, with a topthat is domed or cauliflower-like inshape. Cumulus clouds appear whitewhen they reflect sunlight toward theobserver, but when viewed from di-rectly underneath or when they arebetween the observer and the sun,they may appear dark with brightedges. Over land, cumulus clouds tendto develop during the warming of theday, dissipating at night when the

19


-45

d

20


earth's surface cools. Over water,cumulus clouds tend to develop atnight as the water surface remainswarm while the air mass coolsslightly.

(2) Cumulonimbus. Clouds of this typeare heavy masses which extend togreat heights. Their upper portionsresemble mountains or towers cappedwith a fibrous texture. They developonly in unstable air. Cumulonimbusclouds are distinguished from cumu-lus clouds chiefly by the veil ofice crystal clouds which surroundstheir upper portions. Thunderstorms,squalls, turbulence, and hail are char-acteristic of cumulonimbus clouds.

30. Precipitationa. Description. Precipitation (fig. 4) is visi-

ble moisture that falls from the atmosphere,such as rain, sleet, snow, hail, drizzle, or com-binations of these. As an air mass rises, itsability to hold moisture decreases and cloudsform. When the cloud droplets become toolarge to remain in suspension, rain occurs or ifthe air temperature is below freezing, snow isformed. Sleet is frozen rain formed by dropletspassing through a layer of below-freezing air.Hail consists of rounded particles composed oflayers of ice falling from cumulonimbus cloudswith strong updrafts. Raindrops are carried tohigh altitudes and frozen into ice pellets. Theythen fall and are carried up again by the up-draft until the weight of the pellet is greaterthan the force of the updraft, whereupon itfalls to earth. Freezing rain falls from the airin liquid form but freezes upon contact withobjects on the surface that are at a tempera-ture below the freezing point. The ice formedon these surfaces is called glaze. Air WeatherService observations include information onthe form of precipitation and its character, in-tensity, and amount.

b. Character. The character of precipitationrefers to its duration and to changes in itsintensity. It is reported as continuous, intermit-tent, or showery. Continuous precipitation isthat in which the intensity increases or de-creases gradually. Intermittent precipitation ischaracterized by a gradual change in intensity,but ceases and recommences at least once an

hour. Showery precipitation is marked byrapid changes in intensity and by starting andstopping abruptly. The intensity of precipita-tion is determined on the basis of its rate offall. It is described as follows:

(1) Very light. Scattered drops or flakeswhich do not completely wet an ex-posed surface, regardless of duration.

(2) Light. Not more than 0.25 millimeter(0.01 inch) in 6 minutes.

(3) Moderate. 0.26 to 0.75 millimeter(0.01 to 0.03 inch) in 6 minutes.

(4) Heavy. More than 0.75 millimeter(0.03 inch) in 6 minutes.

c. Intensity. The intensity of snow and driz-zle is determined on the basis of the reductionsin visibility which result, as follows:

(1) Very light. Scattered drops or flakeswhich do not completely wet an ex-posed surface, regardless of duration.Negligible effect on visibility.

(2) Light. Visibility 1 kilometer (5/8statute mile) or more.

(3) Moderate. Visibility less than 1 kilo-meter (5/8 statute mile), but not lessthan 1/2 kilometer (5/16 statutemile).

(4) Heavy. Visibility less than 1/2 kilo-meter (5/16 statute mile).

d. Amount. The amount of precipitation isexpressed in terms of the vertical depth ofwater (or melted equivalent in the case ofsnow or other solid forms) accumulated withina specified time on a horizontal surface. Thisis expressed to the nearest 0.25 millimeter(0.01 inch). A depth of less than 0.13 milli-meters (0.005 inch) is called a trace. In thecase of snow, both the actual depth and theequivalent in water are required. Snow depthis measured to the nearest whole inch, and lessthan 1.3 centimeters (0.5 inch) is termed atrace. The water equivalent of snow is deter-mined by melting a representative sample andmeasuring the resulting depth of water. As anaverage figure, 25 centimeters (10 inches) ofsnow are considered to be equivalent to 2.5centimeters (1 inch) of water, although this issubject to wide variation. The depth of snowis of concern in estimating the trafficabilityand the water equivalent is significant for

21


problems involving water supply, flood predic- pools of air which range in size from about 30tion, stream flow, and drainage.

31. FogFog is defined as a mass of minute water

droplets suspended in the atmosphere at thesurface of the earth that reduces horizontalvisibility. It is formed by the condensation ofwater vapor in the air. The most favorableconditions for the formation of fog are anabundance of water vapor, high relative hu-midity, and a light surface wind. A light windtends to thicken fog. Increasing wind speedswill usually cause fog to lift or to dissipate.Fog usually is more prevalent in coastal areasthan inland because there is more water vaporin the atmosphere. Inland fogs may be verypersistent in industrial regions. In most areasof the world, fog occurs more frequently dur-ing the colder seasons of the year than it doesin the warmer seasons.

32. Stormsa. Thunderstorms. A thunderstorm is a local

storm accompanied by thunder, strong gustsof wind, heavy rain, and sometimes hail, usu-ally lasting for no more than an hour or two.A thunderstorm is cellular, each of its manycells having violent up and down drafts inclose proximity. The overall mass has a charac-teristic frontal zone with violent cool windsracing inward toward the storm in spite of itsforward motion. When a thunderstorm reachesits mature stage and the rain begins, a down-draft starts in the lower and middle levels ofthe storm. This large body of descending aircauses strong, gusty surface winds that moveout ahead of the main storm area, often re-sulting in a radical, abrupt change in windspeed and direction termed the first gust. Ingeneral, the strongest thunderstorm winds oc-cur on the forward side of the storm where thedowndraft first reaches the surface. Thesewinds ascend upward at various rates, depend-ing on the intensity and size of the storm. Theactual storm has layers conducive to icing andhail formation depending on the altitudes ob-tained by updrafts and so on. The speed of athunderstorm wind may reach 80 to 120 kilo-meters (50 to 75 miles) per hour for a shorttime.

b. Tornadoes. Tornadoes are circular whirl-

meters to .8 kilometer (100 feet to one-halfmile) in diameter. A tornado appears as a ro-tating funnel-shaped cloud extending towardthe ground from the base of a cumulonimbus.The low pressure and the high wind speedsencountered in the center of the tornado arevery destructive. The paths of tornadoes overthe ground usually are only a few miles longand the tornadoes move at speeds of 40 to 90kilometers (25 to 55 miles) per hour. Althoughthe maximum wind speeds associated with tor-nadoes never have been measured directly,property damage and other effects indicatethat they may exceed 800 kilometers (500miles) per hour. When they occur over water,tornadoes are termed waterspouts.

c. Tropical Cyclones. A tropical cyclone is alow-pressure system of cyclonic winds thatforms over tropical water areas (fig. 5). Cy-clones of great intensity are called hurricanesin the Atlantic and Eastern Pacific Oceans,typhoons in the Western Pacific Ocean, cy-clones in the Indian Ocean, and willi willi inAustralia. The average life span of a tropicalcyclone is 6 days, although some last only afew hours and others as long as 2 weeks. Tropi-cal cyclones of hurricane intensity are charac-terized by extremely strong and gusty surfacewinds, with speeds of 117 to more than 240kilometers (73 to more than 150 miles) perhour; continuous intense rain in the centralarea, and a relatively calm area near the centerknown as the eye. These storms vary in sizefrom 80 to 800 kilometers (50 to 500 miles) indiameter. The precipitation associated withtropical cyclones is extremely heavy. They arefrequently accompanied by violent thunder-storms, with the heaviest rainfall usually oc-curring some distance ahead of the eye of themoving cyclone. Abnormally high tides are acommon companion of hurricanes and are re-sponsible for a great amount of damage.

33. Weather Forecastsa. Factors. A weather forecast is a predic-

tion of the weather conditions expected to oc-cur at a place, within an area or along a routeat a specified future time. The accuracy andreliability of weather forecasts depend upon anumber of factors, including the climatic char-acteristics of the forecast area, the amount

22


Figure 5. Tropical cyclones.

of weather data available, the reliability ofweather communications facilities, the lengthof the forecast period, and the experience ofthe forecaster. Other factors being equal, thereliability of forecasts generally decreases asthe length of the forecast period increases.

b. Format. Weather forecasts may be pre-sented in coded (numerical), graphical (pic-torial), or written (plain language) format.Normally, weather forecasts for use by Armyunits will be issued in plain language form. Be-cause forecasts are subject to sudden change,they are usually transmitted by electricalmeans. Abbreviations are used extensively.The abbreviations used in weather messagesare contained in AR 320-50 and in the FederalAviation Agency (FAA) publication, Contrac-tions.

c. Sources. Weather forecasts and specialstudies are provided by agencies of the AirWeather Service of the Air Force. Air WeatherService is found on all Air Force bases and onmany Army bases that have Army aviationunits. Division and lower units receive weatherforecasts from either attached personnel ofAir Weather Service or from higher head-quarters.

d. Short-Period Forecasts. These forecastscover a period up to 48 hours in advance ofissue, giving detailed values of the weather ele-ments expected to occur during the period andthe time of anticipated weather changes. Theyare sufficiently reliable for use in detailedshort-range planning.

e. Medium-Period Forecasts. This class covers

a period of 3 to 5 days, and extended-periodforecasts cover periods in excess of 5 days.They are less detailed and specific than short-period forecasts. Usually the weather informa-tion is expressed in terms of departure fromnormal conditions and is suitable only for pre-liminary planning purposes.

f. Severe Weather Forecasts. These providewarnings of weather conditions that will cre-ate unusual difficulties. Examples of severeweather include tropical cyclones, thunder-storms, strong and gusty surface winds, heavyprecipitation, and extremes of temperature.The Air Weather Service furnishes such warn-ings when requested by commanders, basedupon the needs of their particular unit or in-stallation. The weather conditions that will becritical vary with the type of unit or installa-tion. For example, one unit may require warn-ings of winds in excess of 15 to 20 knots, butanother may not be adversely affected by winduntil the speed reaches 35 to 40 knots or more.

34. Weather Intelligencea. Dissemination. Timeliness is the critical

factor in disseminating weather reports andforecasts. Normally they are transmitted byradio or teletype. Weather information is in-corporated in such documents as the intelli-gence estimate, periodic intelligence report,analysis of area of operations, and the intelli-gence summary.

b. Responsibility of Intelligence Officer. Theintelligence officer at corps and lower levels isresponsible for determining the weather infor-mation requirements and submitting them to

23


the Air Weather Service personnel. He informs 3 hours. Chemical Corps smoke battalions cansubordinate units of the weather data requiredby the Air Weather Service and instructs themin the procedure for collecting and forwardingthe data. He disseminates the received weatherinformation and coordinates with G3/S3 in theweather training of subordinate units.

c. Requirements. Weather requirements areof two types-those established by the Armyand passed to the Air Weather Service for ac-tion, and those established by the Air WeatherService and passed to the Army for action. Theintelligence officer coordinates all activitiesdirected toward satisfying these requirements.At division and higher levels this coordinationis effected through the Air Force Staff WeatherOfficer, a special staff officer at those echelons.Below division, the intelligence officer requestsAir Weather Service support through intelli-gence channels. Army weather requirementsmay include climatic information to be used inthe planning phase of an entire campaign oroperation, weather forecasts, reports of cur-rent weather, and weather summaries. Underconditions of nuclear warfare, timely and ac-curate weather data, particularly that concern-ing upper air wind speeds and direction, isessential in fallout predictions. Fallout pre-dictions are required both for friendly andenemy employment of nuclear weapons.

d. Requests. Requests for specific weatherinformation received by the intelligence officerare evaluated to determine whether or not theinformation can be secured by organic agen-cies before they are forwarded to the AirWeather Service. In all cases, before forward-ing the request the intelligence officer insuresthat requests from various units do not overlapand that they cannot be fulfilled from informa-tion already available.

e. Information Sources. Weather data re-quired by the Air Weather Service from Armyunits may be secured by artillery meteorolog-ical sections, Chemical Corps units, Army avi-ation, and forward combat troops. Artillerymeteorological sections are capable of makingwinds-aloft observations and of determiningupper air pressure, temperature, and humidity.In addition. they measure and,report data forfallout prediction and use by the Air WeatherService. This information is transmitted every

furnish information concerning surface windsand temperature. The pilots of Army aircraftare capable of reporting weather conditionswithin their area of flight operations. Forwardcombat units can provide weather data ob-tained by visual observation, and if required,they may be equipped with instruments forobtaining additional weather data.

f. Interpretation. An intelligence officer doesnot merely disseminate verbatim the weatherforecast received from higher headquarters. Hemust interpret it in relation to particular op-erations, He also receives interpretations fromsuch special staff officers as the chemical officer(toxic chemical interpretations and interpreta-tions relative to fallout predictions and travelof fallout clouds), the aviation officer, and theStaff Weather Officer. The weather informa-tion that he transmits to the command must bepresented in its most usable form, with theoperational aspects of the data indicatedwhenever applicable.

35. Effects of Temperaturea. Temperature. Periods of freezing tem-

peratures will increase the trafficability ofsome soils, while with others it may create icesheets on roads, making movement more diffi-cult. Thawing temperatures may make frozensoils difficult to traverse and may damageroads with poor foundations. The ability ofprojectiles to penetrate the earth is decreasedby frozen soil, but freezing increases the cas-ualty effect of contact-fuzed shells. Meltingsnows may cause floods and in mountain areasresult in avalanches.

b. Inversions. Temperature inversions createan exception to the normal decrease in tem-perature that occurs with increases in altitude.In a temperature inversion, the air nearest theground is colder than the overlying air. Thelower air remains stable. Dust and smoke re-main near the ground, reducing visibility andair purity. Inversion conditions are favorableto either enemy or friendly employment oftoxic chemical or biological agents. Radarbeams may also be refracted or ducted due toinversions.

c. Site Selection. In selecting sites to provideprotection against low temperatures in the

24


northern hemisphere, preference should be The speed and direction of the wind are primegiven to the southwesterly slopes of hills andmountains, where the temperature usually ishigher than on other slopes. Cold air flowsdownslope and remains pocketed in incloseddrainage areas or is dammed by forests orother barriers. These cold air pockets have thelowest temperature of the terrain, and oftenare characterized by freezing or fog when ad-jacent areas are frost-free or clear. In areas offrequent calm or near calm conditions suchcold air drainage areas should not be selectedfor troop bivouacs or for such facilities asmotor pools and hospitals. In hot climates, cau-tion is required in utilizing cold air pockets,since they are likely areas for the formationof ground fog and excessive humidity. In windyareas, on the other hand, these pockets provideshelter from the chilling effects of the wind.Areas susceptible to cold air drainage can bereadily located by ground reconnaissance orfrom topographic maps by visualizing the flowof cold and dense air over the terrain. In gen-eral, concave land surfaces facilitate the accu-mulation of cold air, and convex surfaces favordrainage of air from the surface. Toxic chem-ical and biological aerosols also tend to collectin depressions and low places. In areas whereheating is required, careful selection of theterrain in locating bivouacs and other instal-lations will save fuel. If temperature data areavailable for various possible sites, or can beestimated by altitude factors and terrain con-figuration, fuel requirements may be closelyascertained. Toxic chemical agents vaporizemore rapidly in high ambient temperaturesthan in low ambient temperatures. The effectsof weather on toxic chemical and biologicalagents, and on radiological contamination, arediscussed in FM 3-5 and TM 3-240. Temper-ature has no significant effects upon the in-tensity of blast or the thermal radiation ofnuclear weapons.

36. Windsa. Description. In arid or semiarid areas,

strong winds frequently raise large clouds ofdust and sand which greatly reduce observa-tion. Similar effects result in snow-coveredregions, where blowing snow may reduce visi-bility over wide areas. Observation aircraftmay be grounded entirely during such periods.

considerations in areas contaminated by toxicchemical agents, biological agents, and radio-logical fallout. Winds of 5 to 16 kilometers (3to 10 miles) per hour provide the most favor-able conditions for the employment of contam-inating agents. Winds below or above thatrange cause a loss of effectiveness in the useof gas, smoke, chemicals, radioactive clouds,and mists. The direction of the wind must beconsidered for the protection of friendly troops.In areas characterized by great turbulence andvariable winds the use of contaminatingagents is highly dangerous.

b. Projectiles. Winds tend to deflect projec-tiles from their normal paths, particularlywhen they are fired at long ranges. The effectthat wind will have on a projectile increaseswith an increase in the velocity of the windand the size of the projectile. To obtain ac-curacy in artillery fires, the direction andvelocity of the wind must be known in orderto apply compensating corrections to firingdata. Winds also affect the efficiency of sound-ranging equipment.

c. Parachute Landings. Parachute landingsare feasible in winds up to 25 kilometers (15miles) per hour. At higher velocities, the windtends to scatter troop concentrations, to foulequipment, and increase the number of casual-ties from landing accidents. Strong winds alsoincrease the time that parachutists must re-main in the air, as well as the time required tosecure equipment and prepare for combat afterlanding.

d. Amphibious. Strong winds hinder amphib-ious operations by creating high seas whichwill prevent landing craft from landing or re-tracting.

e. Nuclear. Wind speed and direction haveno influence upon the blast or thermal radia-tion effects of nuclear weapons, nor upon therange of the initial nuclear radiation. Windsat all atmospheric levels are significant factors,however, in determining the location of radio-logical fallout resulting from the surface, sub-surface or airburst of a nuclear weapon. Con-taminated dirt and debris carried upon thecolumn and cloud will be deposited downwind.

f. Aerosols. The effectiveness of toxic chem-ical and biological agent aerosols is influenced

25


by the direction and speed of the wind. Such connaissance. Dense clouds above the cameraaerosols are dissipated rapidly in high winds.The use of toxic chemical agents in vapor formis most effective on clear or partially clearnights when the air usually is most stable.

g. Radar. Strong winds can damage radarantennas or even prevent use of the radar.

37. Effects of Humiditya. Ballistics. The effects of humidity upon

ballistics are important because of the rela-tionship of humidity and density. The amountof water vapor in the air affects the trajectoryof projectiles by the influence that it has uponair temperature and density. Humidity alsohas an effect upon the distance that soundstravel, thus affecting sound-ranging opera-tions. Humidity does not seriously decrease theeffectiveness of most toxic agents and may in-crease the effectiveness of some, such as blistergas. The effectiveness of some biological agentaerosols may tend to be increased by moisturein the air since living organisms are affectedadversely by dry air and direct sunlight.

b. Smoke. In the use of a screening smoke, ahumidity of 90 percent will have twice the ob-scuring effect of a humidity of 40 percent.With this increase in relative humidity, onlyone-fourth of the amount of smoke-producingmaterial need be used.

c. Nuclear. Humidity has no influence uponthe blast effect or nuclear radiation of a nu-clear weapon and no direct effect upon thermalradiation intensities. It will affect target vul-nerability to a degree, because it will determinethe moisture content of clothing, structures,equipment, and vegetation and their suscepti-bility to ignition. This effect is pronounced,however, only when a very high or very lowrelative humidity has prevailed over a longperiod.

38. Cloudinessa. Effects. Daytime cloudiness reduces the

amount of heat received from the sun at theearth's surface, slowing down the drying ofroads and affecting the trafficability of soils.Extensive night cloudiness prevents the loss ofheat from the earth's surface due to radiationalcooling and results in higher nighttime tem-peratures. Cloudiness chiefly affects air oper-ations by limiting aerial observation and re-

level may reduce light intensity to the pointthat photography becomes difficult or impossi-ble. A high, thin layer of clouds, on the otherhand, may eliminate ground shadows and thusimprove the quality of aerial photographs. Incloudy areas, close combat air support may beprohibited or restricted to aircraft equippedwith suitable navigation instruments.

b. Searchlights. Low-lying clouds may beused to advantage -by reflecting searchlightbeams to illuminate the ground surface. Anyconsiderable degree of night cloudiness reducesthe amount of moonlight that reaches theground. If the fullest utilization of twilightperiods is desired, the extent of cloud covermust be considered.

c. Nuclear. Clouds have no influence uponthe blast effect of nuclear weapons that areburst below them, nor do they affect nuclearradiation, but they may affect the intensityof thermal radiation reaching a target. If aweapon is burst above or within a continuouscloud layer over the target, a large portion orall of the thermal radiation may be attenuated,with a serious loss of effect. The amount ofloss will depend upon the thickness and con-tinuity of the cloud layer and the position ofthe burst with respect to it. If a weapon isburst below a continuous or nearly continuouscloud layer, some of the thermal energy may bereflected from the cloud layer downward on thetarget area, enhancing the total thermal effect.

39. Rainfalla. Amount. When planning extended oper-

ations, the average amount of precipitationoccurring in the proposed area must be con-sidered. An area with 50 centimeters (20inches) or less of rainfall in a year normallywill not have adequate supplies of water formilitary purposes. Rainfall of 50 to 200 centi-meters (20 to 80 inches) a year presents noserious problems in operations, other thanthose that occur in rainy seasons through local-ized flooding and poor soil trafficability. An-nual rainfall in excess of 200 centimeters (80inches) generally hinders normal operationsduring the seasons that the greater amount ofthis rainfall occurs. The seasonal and dailycycle of precipitation (fig. 6) affects the sched-uling of military activities. Seasonal distribu-

26


Figure 6. Seasonal distribution of rainfall.

tion may be uniform throughout the year or itmay occur in distinct wet and dry periods. Inthe monsoon areas of southeast Asia, for ex-ample, the rains come suddenly and with suchviolent downpours that some military oper-ations must cease almost entirely, and plansmust be revised. During rainy seasons in mosttropical or semitropical areas, there usually arepredictable periods of maximum rainfall oc-curring at certain times of the day which mustbe considered when planning constructionwork or tactical activities. The maximum rateof precipitation expressed in inches per day orhour may also be critical in designing culvertsor other facilities for draining excess water.

b. Trafficability. Precipitation affects soiltrafficability and hence cross-country move-ment. In areas of seasonal precipitation, thecross-country movement characteristics of anarea may change drastically each season. Sea-sonal floods may swell or flood streams, mak-ing fording and bridging operations difficultor impossible. Snow and sleet hamper move-ment on roads in winter, often making themimpassable in mountainous areas. The snowthat accumulates in mountains during thewinter months frequently affords a water sup-ply throughout the year to lower, drier re-gions.

c. Visibility. Precipitation usually has anadverse effect on visibility and observation,although rain sometimes may wash excessiveimpurities from the air. Rain and snow aid

concealment, and may facilitate surprise at-tacks. Operation of listening and sound-rang-ing posts is often limited by precipitation.

d. Neutralization. Rain and snow normallyreduce the effectiveness of toxic chemical andbiological agents. Heavy or lasting rain washesaway these agents and may neutralize them.Snow may cover liquid toxic agents so thatlittle vapor or contamination hazard appearsuntil the snow melts. Heavy precipitation willtend to dilute the concentration of biologicalagent aerosols.

e. Communication. Precipitation may havean adverse effect upon communications, reduc-ing the range of field wire circuits and pro-ducing radar "clutter" which tends to obscuretarget echoes.

f. Nuclear. Precipitation has a significantinfluence upon the blast effect of a nuclearweapon, but no effect upon initial nuclear radi-ation. It affects the range of thermal intensityto the degree that it reduces visibility. Build-ings, equipment, debris, vegetation, and othernormally flammable elements will requirehigher thermal intensities for ignition, and thespread of primary or secondary fires will belimited. Residual radiation may be affected.If the radioactive particles formed in an air-burst are ingested into rain-bearing clouds,the nuclear cloud (if it does not rise above therain-bearing clouds) will become so mixed withthe rain cloud that it will become an integralpart of the rain-producing system. The radio-

27


active material will be deposited with the rain surface, possibly concentrating it in otherover a large area. Heavy rain over an areawould wash away some of the material from acontaminating burst, either air, surface or sub-

areas where there are watercourses, lowground, drainage system, or flat undrainedareas.

Section II CLIMATE

40. Definitiona. Elements. Climate (fig. 7) refers to the

general variation and pattern of the primaryclimatic elements which include temperature,precipitation, humidity, winds, and air pres-sure. It is a composite or generalization of theday-to-day weather at a given place or areaover a long period of time. The strength and

direction of winds, amount of precipitation,and average temperatures (figs. 8 and 9) thatwill prevail in an area can be approximated,based upon statistics compiled for previousyears. These climatic elements may be de-scribed by graphs or charts in terms of means,ranges, average maximums and minimums, ex-tremes, and frequencies of occurrence.

Figure 7. Major climate regions.

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Figure 7-Continued.

Figure 8. World temperatures in January.

b. Terrain. Although the heat transmittedby the sun to the earth is the dominant factorin weather and climate, terrain has a majoreffect upon the climate in many regions. Highmountains can block the movement of airmasses and act as climatic divides. Terraincan also effect differences in climate between

land and ocean areas, where the land hashigher summer temperatures and lower wintertemperatures than the adjacent body of water.Local terrain influences may also be highlysignificant in military operations. The groundconfiguration often strongly affects the patternof occurrence of fog, surface winds, and other

29


Figure 9. World temperatures in July.

conditions. Information about these local con-ditions frequently can be obtained only by theanalysis of topographic maps, ground recon-naissance, and the interrogation of inhabi-tants.

c. Plants. The influence of climate on thegrowth of plants is a predominant factor intheir distribution, and the relation betweensoil formation and climate is so close that thepattern displayed by a soil map will provide anindication of the climatic conditions.

41. Tropical Rainy Climatesa. Rain Forest Climate. The tropical rain

forest climate occurs in a belt generally extend-ing from 50 to 8 ° on either side of the Equator.In some regions, such as the Amazon Basinand the Congo Basin, the air is always hot anddamp, there are frequent torrential rains ofshort duration, and the winds are feeble orabsent for long periods of time. This climatictype is also found on windward coasts, where,between latitudes of 5° and 25 °, easterly tradewinds blow almost constantly over hills ormountains. The cooling of these winds as theyrise over the barriers produces an extremelyheavy rainfall. This occurs, for example, inportions of Hawaii, the Philippines, the easterncoasts of Central America, Brazil, Madagascar(Malagasy), and most of the islands in thesouthern Pacific Ocean. In this type of climate,the rays of the sun are nearly vertical most ofthe time, so that days and nights are prac-

tically equal in length throughout the year.Night temperatures usually are a few degreeslower than daytime temperatures. There areno clearly marked seasons. Relative humidityis high at all times, and cloudy weather pre-vails. There are heavy rains on at least 4 or 5days each week during the rainiest months,with the greatest amounts during the periodswhen the sun is most directly overhead. Therains are torrential, often accompanied bythunder and lightning. Ordinarily the rain be-gins in the afternoon, when the heated air isrising most rapidly, and ends before nightfall,although occasionally a light rain will continueinto the night.

b. Savanna Climate. The tropical savannaclimate occurs generally in the regions from5° to 15° on either side of the Equator, betweenthe dry climates and the tropical rain forestregions. Instead of the dense forests typical ofthe tropical rain forest climate, the savannaregions have more open forests and large areascovered with tall grasses. Savanna regionshave high temperatures, with annual ranges(difference between mean temperature of thewarmest and coldest months of the year) vary-ing between 5° and 15° F. The total amount ofrainfall is less than that of the tropical rainforest climate. There are distinct wet and dryseasons, and usually the rainy season beginsand ends with squalls and violent thunder-storms. During the rainy season, periods ofintensely hot sunshine also alternate with

30


brief, violent deluges of rain. The amount of is meager and erratic. Steppe regions on therainfall varies considerably, so that there areyears of drought and years of flood. In the dryseason the weather resembles that of desertregions, with very little rainfall. Trees losetheir leaves, many small streams are dry, andthe soil becomes hard and cracked. Visibilityis greatly reduced by dust and the smoke fromgrass fires.

c. Monsoon. In certain parts of southern andsoutheastern Asia, the climate is greatly in-fluenced by monsoon winds. The wet and dryseasons coincide respectively with the onshoreand offshore winds.

42. Dry Climatesa. Description. Dry climates are those in

which the evaporation rate exceeds the pre-cipitation rate. The dry climates are locatedon the leeward interior portions of continents.There are two subdivisions: the arid or deserttype, and the semiarid or steppe type. In gen-eral, the steppe is a transitional region sur-rounding the desert and separating it from thehumid regions. Dry climates are characterizedby extreme seasonal temperatures with largeannual ranges. Daily ranges also are high.Humidity is relatively low, averaging from 12to 30 percent around the middle of the day.Generally the skies are clear and cloudless.Because vegetation is meager, the barren sur-face of the dry earth becomes very hot duringthe day and cools rapidly at night. The vegeta-tion offers little friction to the moving air,and accordingly, strong, persistent winds aretypical of desert regions.

b. Low-Latitude Desert Climates. These oc-cur in the vicinity of 20 ° to 25' north or south,with the average positions of their extrememargins at approximately 150 and 30°. TheSahara and Australian Deserts are typical ex-amples of this type of climate. In these desertregions, rainfall is not only small in amount,but erratic and uncertain. However, infrequentheavy showers may turn dry streambeds intoraging torrents. Often there is no rainfall forseveral years, and the skies are almost alwaysclear and cloudless.

c. Low-Latitude Steppes. These are semiarid,having a short period of rain-bearing windsand storms each year. Precipitation, however,

poleward sides of deserts have almost all theirannual rainfall in the cool season. Those ad-joining savannas on the equatorward sides ofdeserts generally have a brief period of rela-tively heavy rains during the time when thesun is highest.

d. Middle-Latitude Dry Climates. These oc-cur within the deep interiors of continents, inthe regions surrounded by mountains or pla-teaus that block the humid maritime airmasses. Rainfall is meager and undependable,as in the low-latitude deserts, but there is alsoa season of severe cold. In winter there may bea small amount of snow, frequently accompa-nied by strong winds. The temperature andweather characteristics are similar to thoseof humid continental climates in comparablelatitudes, except that there is less rainfall. Thearea immediately to the east and west of theCaspian Sea is a typical example of thisclimate.

e. Middle-Latitude Desert Climate. Thisclimate is characterized by lower temperaturesand precipitation than low-latitude desert cli-mates. This climate occurs in the basinlike,low-altitude areas, surrounded by high-landrims, that exist in some continental interiors.The Great Basin of the U.S. and the TurkestanBasin of Asia have this type of climate. Sum-mer temperatures are high. Middle-latitudesteppes occupy intermediate locations betweendeserts and humid climates. They have smallamounts of rainfall, which is usually unpre-dictable in amount or time of occurrence.

43. Humid Mesothermal Climatesa. Description. These climates are character-

ized by moderate temperatures that occur in aseasonal rhythm. They are divided into threegeneral categories-Mediterranean climate,humid subtropical climate and marine westcoast climate.

b. Mediterranean Climate. This climate hashot, dry summers and mild winters, duringwhich most of the annual precipitation occurs.Annual rainfall usually ranges from 38 to 64centimeters (15 to 25 inches). In the wintermonths, the average temperature is usuallybetween 40 ° and 50°F.; in the summer, itranges generally from 700 to 80 ° F. This type

31


of climate occurs in five regions-the border- tropical air mass, then be reduced by a sub-lands of the Mediterranean Sea, central andcoastal Southern California, central Chile, thesouthern tip of South Africa, and parts ofsouthern Australia. Coastal areas often have amodified type of Mediterranean climate, withcool summers accentuated in some areas by thecool ocean currents offshore. There is apt to bea cool daily breeze along the seacoast and for ashort distance inland. Relative humidity ishigh. Fogs are frequent, but usually are dissi-pated by the heat of the sun in the early morn-ing hours. Winters are mild and frost infre-quent, and the annual change in temperatureat some locations is uncommonly small. Sum-mer days in Mediterranean climates are warmto hot, with bright sunshine, low relativehumidity, and nearly cloudless skies. Dailyweather becomes erratic and unpredictable inautumn. The winds are less regular and thereis occasional rain. Temperatures remain rela-tively high. Winters are mild and warm, withoccasional frosts and relatively abundant rain-fall.

c. Humid Subtropical Climate. This climateoccurs in regions located on the eastern sidesof continents, generally from about latitude25° poleward (north or south) to 350 or 400.This type of climate is found, for example, inthe American Gulf States. Temperatures aresimilar to those of the Mediterranean climate,with less contrast between regions on thecoast and those located inland. Rainfall rangesfrom 75 to 165 centimeters (30 to 65 inches)a year at most locations. In the summer, hu-midity is high, temperatures average fromabout 75 ° to 80°F. in the hottest month, andthere are frequent thundershowers. Nights arehot and sultry. There is no drought season, butnormally there is less rain in winter than insummer. Severe tropical cyclones occur mostfrequently in the late summer and early fall.Winters are relatively mild in this type cli-mate. Temperatures in the cool months usuallyaverage between 40° and 55°F. with the mid-day temperature around 55° to 60°F. and thenight temperature from 350 to 45°F. The highhumidity, however, makes the nights chillyand uncomfortable. Snow may fall occasion-ally, but it does not remain for more than 2or 3 days. Daytime temperatures may beraised above 60 ° or 70°F. by the arrival of a

sequent polar wind as much as 300 F. in 24hours, resulting in a severe freeze.

d. Marine West Coast Climate. This climateoccurs on the western or windward sides ofcontinents, poleward from about 400 latitude,and results from onshore westerly winds thatblow over the land from adjoining oceans. Itborders the Mediterranean type on its equator-ward margins, extends into the higher middlelatitudes and ends at the subarctic or tundraclimate. Where mountains are closely parallelto the west coast, as in Scandinavia, this typeof climate is confined to a relatively narrowregion on seaward side of the highlands. Inparts of western Europe, where there are ex-tensive lowlands, the effects of the ocean con-ditions have an influence on the climate formany miles inland. Summers are cool with oc-casional hot days but no severe or prolongedheat waves. Rainfall is fairly abundant. Win-ters are mild, particularly in western Europe,where a great mass of warm water known asthe North Atlantic Drift lies offshore. Cloudyskies and a humid atmosphere are prevalent.There are frequent severe frosts. The middaytemperatures of most winter days are rela-tively high. During unusually cold periods,temperatures may remain below freezing forseveral days. The winter season is marked bysevere storms, fogs, and mist. Where the west-ern coasts are bordered by mountain ranges, asin Norway and Chile, precipitation may reacha total of 250 to 380 centimeters (100 to 150inches) a year. In areas consisting predomi-nantly of lowlands, rainfall usually averagesfrom 50 to 90 centimeters (20 to 35 inches)a year and may fall steadily for several daysat a time. In mountainous regions, such as theCascade Range or the Scandinavian Highlands,snowfall is very heavy. The marine west coastclimate is cloudy, and has mist or fog for atleast 40 days a year at many locations.

44. Humid Microthermal Climatesa. Types. The humid microthermal climate

occurs in the Northern Hemisphere northwardfrom the subtropical climatic regions and inleeward interior locations. Latitudinal spreadis from about 400 N to 600 or 650 N. It hascolder winters than the mesothermal type,with larger annual changes of temperature,

32


longer frost seasons and snow cover that lasts e. Subarctic Climate. This climate occurs infor considerable periods. Humid continentaland subarctic are the principal types of micro-thermal climate.

b. Humid Continental Climates. These cli-mates border the marine west coast climaticregions. Where there are mountain barriers, asin North America, the change between the twotypes of climate is abrupt, but it is very grad-ual where there are no barriers, as in the low-lands of western Europe. Seasonal differencesare extreme, with very cold winters and warmto hot summers. Along the seaboard, the sum-mer heat is oppressive and sultry because ofthe higher humidity, and the winter cold ismore raw and penetrating than in the drierinterior regions. Along the interior margins,humid continental climates border upon thedry climates and have subhumid character-istics. The prairies of North America and in-terior Eurasia are examples of such climaticregions. In these areas, the maximum rainfallusually occurs in late spring and early summer,rather than at the time of greatest heat. Inwinter, regions with a humid continental typeof climate normally have a permanent snowcover that lasts from a few weeks to severalmonths. Summer rains usually occur in sharpshowers accompanied by thunder and light-ning. Winter in the prairie regions is charac-terized by frequent changes in weather con-ditions, with occasional blizzards, known asburans. A blizzard is marked by violent gales,drifting snow, and extreme cold. Althoughthere may be no precipitation falling, the airis filled to a height of several hundred feet byswirling masses of dry, finely pulverized snow.Afternoon thunderstorms frequently occur dur-ing summer in prairie regions.

c. Southern Margins. Regions on the south-ern margins of microthermal climates havelong, hot, and humid summers lasting from150 to 200 days between the periods of frost.Winters are cold, with frequent intervals ofmild, rainy weather.

d. Winter. Winter is the dominant seasonon the poleward side of regions with this typeof climate. Summers are relatively short, usual-ly comprising a period of about 5 months. Tem-perature changes of as much as 40° F. in 24hours are common in spring and autumn.

latitudes of 50 ° to 60 ° in the Northern Hemi-sphere. The Eurasian region extends fromFinland and Sweden to the Pacific coast ofSiberia, and in North America, the subarcticstretches from Alaska to Labrador and New-foundland. Long, extremely cold winters andvery brief summers characterize this type ofclimate. Winter quickly follows summer, withonly a short period of autumn intervening. Alarge part of these regions are frozen to a con-siderable depth, with only a few feet of theupper part thawing out in the summer. Thereis little precipitation in subarctic regions. Nomore than 40 centimeters (15 inches) a yearfalls over the greater part of the Siberian area.In most of subarctic Canada the precipitationis less than 50 centimeters (20 inches) an-nually. Precipitation exceeds 50 centimeters(20 inches) chiefly along the oceanic marginsof Eurasia and North America.

45. Polar Climatesa. Location. The poleward limit of forest

growth usually is considered the dividing linebetween polar climates and those of intermedi-ate latitudes coinciding with a line (isotherm)connecting points having a temperature of50°F. for the warmest month. A mean annualtemperature of 320 F. or below is also a dis-tinguishing feature of polar climates. In theSouthern Hemisphere, the only large land areawith a polar climate is the Antarctic continent.In the Northern Hemisphere, this climaticregion includes the Arctic Sea, the borderlandsof Eurasia and North America, with the islandgroups that are north of these continents, andice-covered Greenland. The Arctic is almost alandlocked sea and the Antarctic is a seagirtland with important climatic differences be-tween them. The climate has fewer wide vari-ations in the Antarctic because it is a singleland mass surrounded by oceans with a uni-form temperature.

b. Temperature. Polar climates have thelowest mean annual and summer temperaturesand although the sun remains above thehorizon for 6 months of the year, the rays aretoo oblique to raise the temperature signifi-cantly. Much of the energy from the sun isreflected by snow and ice, and is consumed inmelting the snow cover and evaporating the

33


water. As a result neither the land surface nor 50°F., the ground is free from snow for a shortthe air adjacent to it becomes warm.

c. Precipitation. Precipitation averages lessthan 25 centimeters (10 inches) a year overlarge parts of the polar land areas. Becauseof the low evaporation and small amount ofmelting, permanent ice fields several thousandfeet thick have accumulated on Greenland andthe Antarctic continent.

46. Tundra and Icecapa. Tundra. Polar climates usually are di-

vided into two types-icecap and tundra. Ice-cap climates are those where the averagetemperature of all months is below 32 ° F., vege-tation will not grow, and a permanent snow-and-ice cover prevails (figs. 10 and 11). Whenone or more months in the warm season havean average temperature above 320F. but below

i- .

Figure 10.

b. Temperatures. Average temperatures usu-ally are above freezing only for from 2 to 4months of the year, and killing frosts may oc-cur at any time. Fog is prevalent along thecoast, frequently lasting for days at a time.Snow cover disappears for 1 or 2 months dur-ing the summer season, and the lakes usuallyare free from ice. Drainage is poor because ofthe permafrost, resulting in many bogs andswamps. Summer temperatures do not differgreatly in the various tundra regions. There is,however, a considerable variation in wintertemperatures. Average temperatures in theArctic coastal areas of Siberia average about

period and low sparse vegetation is possible.This climate is designated as tundra. It is lessrigorous than that of the icecap regions. Thewarmest month isotherms of 50°F. on theequatorward side and 32°F. on the polewardside are considered to be the boundaries. Overland areas, tundra climate is confined largelyto the 'Northern Hemisphere. Ocean prevailsin those Antarctic areas where the tundra cli-mate normally would be found. Summers warmenough to develop a tundra climate occur onlyin the most northerly fringes of the Antarcticand on certain small islands of the region. Themost extensive tundra areas are on the ArcticSea margins of Eurasia and North America.Long, cold winters and brief, cool summerscharacterize the tundra climate.

Arctic terrain.

-35 ° to -40°F. in January and February,with even lower temperatures inland. Alongthe Arctic borders of North America, the tem-perature for comparable periods is higher, andwinters are less severe.

c. Precipitation. Annual precipitation nor-mally does not exceed 25 cm to 30 cm (10-12inches) in the tundra regions, although largeramounts are received in parts of eastern Can-ada, particularly in Labrador. Usually the mostprecipitation occurs in summer and autumn,the warmest seasons. Most of it is in the formof rain, with occasional snow. The winter snowis dry and powdery, forming a compact cover.

34


Figure 11. Arctic tundra, showing warm-weather drainage.

Often it is accompanied by strong blizzardwinds which pile up the snow on the lee sidesof hills and in depressions, sweeping exposedsurfaces bare. There is no vegetation to breakthe force of the wind and to hold the snowcover.

d. Icecap. This climate characterizes thepermanent continental ice sheets of Greenlandand Antarctica and the ocean in the vicinityof the North Pole. The average winter-monthtemperatures range from -35 ° to -45°F.Storms or violent winds do not occur as fre-quently in the inner portions of the icecaps asin other climatic regions, but in some marginalareas there are extreme gales caused by theprecipitous descent of cold air from the con-tinental ice plateau.

47. Climatic Studiesa. Records. Climatic studies are based upon

the records of past weather in a given areacompiled over a long period of time. They areused in preliminary planning to provide anestimate of the climatic averages that may be

expected during the period of the proposed op-erations. These studies are of particular valuein developing new equipment and in anticipat-ing logistical problems. Special climatic stud-ies may be prepared covering winds, rainfall,tides, sea conditions, state of ground, and simi-lar aspects of a specified area. Such studieshave been made, for example, to provide datafor use in determining-

(1) Location of camps, training areas,depots, and landing fields.

(2) Coastal areas most suitable for am-phibious operations.

(3) Operations of aircraft over certainmountainous areas.

(4) Smoke behavior in specified localities.(5) Seasonal fuel requirements by weight,

quantity, and type.b. Requests. Requests for climatic studies

should be made as far in advance as possible,and should provide all pertinent information,including mission, area and time, operationallimits, flexibility permitted, and the form ofpresentation.

Section III. OPERATIONS IN EXTREME CLIMATES

48. Desert Regionsa. Weather. High summer temperatures are

normal in desert areas; the summer maximum

may reach 120' to 130°F. During daylighthours the thermal action may be so violentthat planes cannot operate safely at lower alti-

35


tudes. The variation between day and night the mines. In heavy dust and sandstorms, thetemperatures is great, the temperature oftendropping below the freezing point in winter.These sudden changes in temperature occa-sionally give rise to winds of hurricane forcethat carry large quantities of dust and sand.Under these conditions, visibility is very poorand movement may be impossible. Climaticconditions in desert areas also increase main-tenance requirements of mechanized units.Rain is infrequent in desert regions, usuallyaveraging less than 25 centimeters (10 inches)a year, but it may come in sudden downpours.Water sources are few, and frequently are pol-luted and brackish. Usually water for militaryforces must be transported by tank truck, rail,or pipeline from sources outside the desertarea. Winds blow almost constantly in thedesert, frequently limiting the use of smokeand other chemical weapons. Minefields maybe made useless by the blowing dust and sand.The wind either blows away the sand, expos-ing the mines, or deposits large quantities ofit on the minefield, preventing detonation of

operations of mechanized units are similar tothose conducted at night.

b. Natural Features. There are few land-marks in a sandy desert region. The mostprominent features are the huge dunes createdby sandstorms (fig. 12). Usually the surfaceof a sand dune is packed firmly by the windfor a depth of about 5 centimeters (2 inches).This surface will support considerable weight,but detours may be necessary because many ofthe dunes are high, with steep slopes. Areas ofloose sand impede movement on foot or bywheeled vehicles, but tracked vehicles are ableto operate in shallow sand. In flat, hard-surfaced areas, roads and trails are not neces-sary and all types of vehicles can move cross-country. Salt marshes, dry lakes, and wadis(dry streambeds) occur along coastal areas orinland in depressions. Wadis and dry lakes areimpassable when wet and contain a powderysilt when they are dry which may cause ve-hicles to bog down.

, V :,~~~~~~ -__ . 6.

11 .. .. ...... '~>7··;- 4

4 tI rL~~i·

M_

..:... I '

Figure 12. Sand dunes (Death Valley, California).

36

'7i

--_4"


c. Manmade Features. Well-defined roads in summer and are evident in a wideare scarce in desert regions, although thereusually are trails between water sources. Occa-sionally flash floods may cut the routes forshort periods of time. Dust and sa'nd stormsmay prevent traffic through lack of visibilityand maintenance difficulties. A surfaced mainsupply route is essential and usually must beconstructed. Road location is difficult and time-consuming, requiring extensive map study andarea reconnaissance. Buildings must be strongenough to withstand the frequent high windsand constructed tightly to reduce the infiltra-tion of blowing sand and dust. Field fortifica-tions in sand require adequate strengthening,with a maximum use of sandbags. In rockydeserts, field works can be installed only withgreat difficulty. Field fortifications are easy todig in sandy deserts, but they must be revetted,and may be filled quickly with drifting sand.

d. Military Aspects.(1) Key terrain features. In desert op-

erations, terrain features usually arenot major objectives, since the posses-sion of a particular piece of groundseldom contributes materially to thedestruction of the enemy force. Oasesand other water sources are alwayscritical, however, because an adequatewater supply is a fundamental re-quirement of military operations inarid or semiarid regions.

(2) Observation and fields of fire. Thebrilliant sunlight of desert areas re-flected from the light colored groundsurface creates a glare. An observerwith the sun to his back may seewell, but the glare greatly reducesvisibility when he faces toward thesun. He loses his depth perception andwill confuse objects which are inshadows or haze. On hot days, a shim-mering haze may nullify ground ob-servation at ranges of 450 meters(500 yards) or less, depending onlocal conditions. An optical phenom-enon encountered in desert regions isthe mirage, an effect produced by lay-ers of air of varying density acrosswhich the observer sees reflections,usually inverted, of some distant ob-ject or objects. These occur frequently

arc which increases as the sun be-comes higher in the sky. The effect ofa mirage generally is the distortionof objects, particularly in the verticaldimension. This has an adverse effectupon observation, making it partic-ularly difficult to identify vehicles.Distances in deserts are underesti-mated. Shadows on the light-coloredterrain can be seen for miles but tendto distort distant objects. Moonlightin desert areas is much brighter thanin other regions and nights usuallyare very clear, with the haze andglare eliminated. Observation at nightmay be better than during some pe-riods of the day. In open terrain,sound- and flash-ranging are particu-larly effective. Artillery observers,however, may find few positions thatwill allow a commanding view of theterrain. The ability of a weapon tofire effectively in the desert usually islimited only by the range of theweapon and the ability of the ob-server to adjust fire. There is littlevegetation or relief to mask weapons.

(3) Cover and concealment. Cover fromenemy fire may be afforded by sanddunes, hills, and other irregularitiesin the desert terrain. Concealment ishard to obtain, since the vegetationis sparse. Camouflage is used more ex-tensively in desert areas than in nor-mal terrain, and reliance must beplaced upon artificial means. Camou-flage from air or ground observationis extremely difficult to achieve. Themovement of troops during daylightis greatly restricted due to the lackof concealment and cover from air at-tack and troops must be widely dis-persed.

(4) Obstacles. There are relatively fewmajor obstacles to movement in mostdesert regions. Although the road netis limited, cross-country movementmay be good, varying with the type ofsurface materials.

(5) Nuclear weapons. The ease of disper-sion in desert areas avoids a concen-

37


tration of troops that could providea profitable target for nuclear weap-ons. Suitable targets are provided,however, by airfields, communicationcenters, and supply installations.

(6) Toxic chemical and biological agents.Two characteristics of desert regionswhich limit the employment of toxicchemical agents are the sparseness ofvegetation and the extreme variationsin ambient temperature. Toxic agentspresent storage problems because ofthe wide temperature ranges and theextreme conditions existing duringthe day. Effective use of toxic chem-ical agents usually is limited to night.The direct sunlight and dry air whichcharacterize desert regions may pre-sent unfavorable environmental con-ditions for some biological agentaerosols.

(7) Screening smokes. Under desert con-ditions when the winds are still,large-area smoke screening is of con-siderable importance because of thenormal lack of adequate natural con-cealment and cover.

49. Tropical Regionsa. Weather. Excessive heat and humidity

except in tropical deserts characterizet r o p i c a l regions throughout the year.In the rain forest type of climate, there is littleseasonal variation in temperature. The weatheris marked by sudden changes, with torrentialrains that end abruptly to be followed at onceby bright sunshine. Humidity tends to remainhigh because the vegetation checks evapora-tion. Although monsoon areas have a dry sea-son, the total rainfall is so great that rainforest vegetation is dominant. High tempera-tures prevail in the tropical savanna regions,which have distinct wet and dry seasons; butin most of these areas, grass is the predomi-nate vegetation. Both rainfall and relativehumidity are high in the wet season, and rain-fall is rare and relative humidity ranges fromlow to high.

b. Natural Features. Military operations intropical regions are influenced chiefly by therain forest vegetation. In some areas, such asthe Amazon Basin of South America, and in

central and west Africa, the rain forest con-sists of several stories of trees, the foliage ofwhich forms a dense canopy, preventing sun-light from reaching the forest floor, and thusprecluding dense undergrowth. In other areas,such as in Southeast Asia and some islands inthe Pacific Ocean, where a monsoon climate pre-vails, the rain forest has a canopy only partlycontinuous and a dense undergrowth. Rainforest is commonly called "jungle," but theterm "jungle" is not recognized as a vegetationtype. Terrain covered by the rain forest variesfrom mountain ranges to low, swampy plains.In Southeast Asia, the Pacific Islands, and partsof Latin America, the rain forest covers ir-regular terrain. Other rain forest areas, suchas those in central Africa and South America,generally are low and level. Some coastal por-tions of rain forest areas are characterized bymangrove swamps or by open beaches linedwith bamboo or coconut groves. Beyond theshoreline there may be paddy fields or pine-apple, coconut, sugar cane, or rubber plana-tions. Between these and the rain forest theremay be low-lying foothills covered with brushor tall grass. Streams are numerous in rainforest areas, but they are generally muddy andsubject to sudden floods. In wet seasons an en-tire area of flat rain forest may become a con-tinuous swamp. In mountainous areas streamsthat normally are shallow become torrentialshortly after a heavy rain. The characteristicsof rain forest terrain and its effects upon mili-tary operations are discussed in FM 31-30.

c. Manmade Features. There are few roadsor trails in rain forest areas. Usually roadsmust be constructed, and the use of these islimited to light trucks or light tracked ve-hicles. Except for coral in some coastal areas,there is a lack of materials suitable for roadconstruction. The dense vegetation, unstablesoils, and poor drainage make roadbuildingdifficult. To establish and maintain a road netof even minimum standards calls for greaterengineer effort than in other types of terrain.Navigable waterways often provide the mostefficient routes of communication, althoughthey are highly vulnerable to ambush. Bridgessuitable for military loads rarely exist injungle regions. The construction of bridges iscomplicated by the frequency and intensityof flash floods, the tendency of some jungle

38


streams to shift their courses, and the rapid readily noticeable from the air. Be-decay of wooden structural members. Engi-neers must be prepared to repair or replacebridges rapidly at short notice. Aerial tramsare useful because of the deep cuts made byjungle streams in hilly or mountainous ter-rain. Towns and villages in jungle regionsrarely provide suitable facilities for militaryinstallations. Usually settlements are avoidedfor hygienic reasons. Excellent anchorages maybe found along many tropical coasts, but thereare very few water terminals sufficiently de-veloped to be of any value in military opera-tions.

d. Key Terrain Features. In jungle areas,the key terrain features generally are thosethat provide control of trails, navigable water-ways, and beaches suitable for amphibiouslandings. Possession of the edges of an areaof high rain forest could provide observationpoints, thus giving advantages similar to thosederived from the possession of high ground.

e. Observation and Fields of Fire.(1) Observation. In rain forest, the dense

vegetation often limits observation toshort distances. Usually the canopyin a primary rain forest, which con-sists of a virgin growth of maturetrees, is so thick that it cuts off mostsunlight, and visibility is limited toabout 20 or 30 meters (20 or 30yards). Visibility may be limitedabout 5 meters (5 yards) or less inthe secondary forest, which is com-posed of a second growth that de-velops when the original forest hasbeen burned off or cut. Rain, clouds,and the steamy exhalation from wetareas also tend to reduce visibility.Because of the limited visibility andthe lack of conspicuous landmarks, itis often difficult to locate a groundposition from a map. Camouflagefrom close ground observation is ofthe greatest importance in the rainforest. In most areas, however, thereis less need for artificial camouflageagainst air observation. Wheneverpossible, the natural overhead is pre-served, since any break in thenormally uniform tree canopy is

cause observation is limited, tacticalunits must employ narrow frontages,reduced distances and intervals be-tween elements, increased patrol ac-tivity, and a larger number of liaisonparties than required in more openterrain. The difficulties of observationgreatly restrict the employment ofsupporting arms and weapons. Artil-lery forward observer teams on theground usually cannot see the burstand must adjust fire by sound spot-ting and sound sensing methods.Aerial forward observers may be uti-lized with a higher degree of reli-ability. Data based on maps orphotomaps can be used only to alimited extent.

(2) Fields of fire. Since natural fields offire generally are limited to about 5or 10 meters (5 or 10 yards), lanesmust be cleared. Where the under-growth is heavy, several days of laborwill be required to clear 90-meter(100-yard) fire lanes around a posi-tion. In order to avoid revealing wea-pon positions, a fire lane in densevegetation usually is in the form ofa tunnel from 1 to 3.5 meters (1 to4 yards) wide, with the overhangingfoliage left intact. In rain forest, themost effective weapons are those thatcan be supplied easily with ammuni-tion and are readily transportableover difficult terrain. Suitable wea-pons include mortars, machineguns,automatic rifles, and grenades. Arm-ored vehicles cannot move throughrain forest unless routes have beenprepared. Usually the movement oftanks is limited to beaches, coconutgroves, clearings, and improvedtrails. The principal value of tanks isin the use of their flamethrowers, di-rect fire weapons, and crushingweight in the destruction of enemyfield fortifications. Tanks are highlyvulnerable to ambush and close in at-tack in rain forest terrain. Becausethe heavy vegetation reduces the ef-

39


fective bursting radius of artilleryshells, weapons of 105-mm or highercalibers must be employed to blastaway jungle undergrowth and destroyenemy positions. Artillery piecesshould be capable of high-angle fireand should be drawn by tractors ortransported by helicopters. Engineerequipment must be available for theimprovement of trails, construction offiring positions, and clearing of fieldsof fire. In some mountainous areas,only pack artillery may be practica-ble. Air forces are effective in closetactical support of ground elements,but their utility for tactical bombingis less than in other types of terrain.Armed helicopters are used extensive-ly in close support of ground forces.

f. Cover and Concealment. Rain forest pro-vides concealment from air and ground obser-vation and may furnish some cover from smallarms fire. The amount of cover given by slittrenches and other field fortifications is oftenlimited by the high water table, which pre-vents excavating more than a few feet belowthe surface of the ground.

g. Avenues of Approach. Cross-countrymovement in rain forest is slow and difficult.Troops may have to cut their way through con-tinuous thick undergrowth or make lengthy de-tours to avoid impassable swamps. On mosttrails, troops must move in a column of files,and the average rate of movement rarely ex-ceeds 1.5 km per hour. Usually foot movementmay be made most easily on ridges, where thevegetation is more open and the better drain-age results in less muddy surfaces. Except forsmall, fast streams with traversable beds,movement is poorest along the banks of rivers,because of the dense vegetation, mud, swamps,and tributary streams. Even in comparativelydry weather, mud slows down vehicular trafficin the jungles. It may be necessary to supple-ment motorized transport by the use of heli-copters and carrying parties. Jungle roads andtrails rapidly disappear unless they are in con-stant use. Accordingly, maps showing thesefeatures seldom are reliable. Air photographsof jungle terrain rarely reveal more than thetreetops.

h. Communications. Visual signaling is sel-dom effective in the rain forest because of thedense growth. The use of messengers is slowand may be hazardous. Wire circuits are hardto install and maintain. The range of radiosets may be greatly reduced by the vegetation,resulting in ranges from 40 to 70 percent lessthan those considered normal in open or light-ly wooded terrain.

i. Toxic Chemical and Biological Agents.Both the weather and terrain conditions inrain forest areas are favorable for the em-ployment of chemical and biological agents.Where the overhead canopy is very dense, how-ever, sprays from aircraft usually are onlymoderately effective against personnel. Thelarge-scale use of defoliants will increase thefields of fire of weapons, and provide increasedobservation.

50. Arctic and Subartic Regionsa. Weather. Severe changes in weather are

common in arctic and subarctic regions. Thesechanges include shifting periods of severefrosts, mild weather, sudden freezing, snow-storms, strong winds, and dense fogs. Reliableand timely weather forecasts are essential toguard against damage to equipment and instal-lations and to gain any tactical advantagesthat may be possible by exploiting changes inweather conditions. Arctic operations fre-quently are hindered by strong winds, whichusually occur more often along the coast thanin the interior. Wind speeds in excess of 128kilometers (80 miles) per hour have been re-corded at coastal stations. Winds blow con-tinually, and in most areas there are no hills,mountains, or other natural barriers to pro-vide protection. Blowing snow constitutes aserios hazard to flying operations. Winds of16 to 24 kilometers (10 to 15 miles) per hourwill raise the snow several feet off the ground,obscuring such surface objects as rocks andrunway markers. The short days and longnights of winter reduce the amount of daylightavailable for tactical operations and work ac-tivities. Nights often are bright because of theillumination of the moon, stars, aurora bore-alis, and reflections from the snow, so thatnight movements are possible. The short sum-mer nights permit military operations throughthe 24-hour period.

40


b. Natural Features. Following a heavysnowfall, landmarks and other objects becomecovered, making orientation difficult. Gulliesand ditches are filled and obscured so thatmovement is made more hazardous. The freez-ing of swamps and lakes may convert obstaclesinto avenues of approach for the enemy.Warmer temperatures in spring will createthaws and mud in the subarctic, causing riversand streams to overflow. In mountainous orhilly country, landslides can be expected in thespring, as the result of boulders and smallerrock formations expanding from the warmthof the thawing temperatures.

c. Manmade Features. In the subarctic,routes of communication and transportationare affected by every heavy snowfall and traf-fic may come to a halt. Strong winds causesnowdrifts requiring a constant clearing ofroutes, and transportation is slowed greatlyby ice and sleet. To avoid these drifts, roadsmay be routed through woods, where driftsseldom occur, or along the crest of high groundwhere the snow usually is less deep. In ex-tremely cold temperatures, railroad operationis restricted. Blocked tracks and derailmentsare frequent; switches often are frozen; snowand rock slides, washouts, and frost heavingdamage the lines; and the ice caused by waterseepage must be cleared from tunnels beforethey can be used. Excavation is difficult ineither frozen or thawed ground. In frozenground, handtools are ineffective. Explosivesare effective, but they must be employed inquantities greater than required in other ter-rain. Gravel is easier to excavate than soil,because it has better drainage and accordinglydoes not freeze as solidly. Foxholes, trenches,breastworks, and emplacements may be pro-vided by digging into the snow or through itinto the underlying ground. Snow trenchesusually need revetting. In very deep snow, tun-nels may be dug to provide concealment. Theyfurnish cover from small arms fire, but do notgive protection from artillery fires. The springthaws in subarctic climates must be consideredwhen planning structures and fortifications.Bunkers, trenches, and other field fortificationsmust be designed and sited so as to insure gooddrainage. In the thawing period, roads in low-lying areas and bridges are apt to be washedout. Floating ice will destroy or damage

bridges of temporary construction. Runwaysand landing strips will require considerablemaintenance. Airfields that have been improp-erly designed and constructed may becomewholly inoperative for extended periods.

d. Observation and Fields of Fire.(1) Observation. Arctic air is exception-

ally transparent, providing visibilityover long distances. There is a lack ofcontrast between objects, however,particularly when they are coveredby a layer of new snow. Observationin the Arctic is restricted chiefly byfog, blowing snow, and local smoke.The latter is a serious problem onlyin the vicinity of larger settlements,where it often accompanies the shal-low radiation fogs of winter. A radi-ation fog results from the radiationalcooling of air near the surface of theground on calm, clear nights. Depthperception is adversely affected byarctic conditions, principally by theextremely clear, dry air, the lack ofcolor differences, and the diffusingeffect of light on the crystalline sur-face of the snow and ice. A hazardousphenomenon that reduces visibility tonear zero is the whiteout. When thiscondition exists, the horizon, shadows,and clouds are not discernible, andonly very dark objects can be seen.The amount of light reflected from asnowcovered surface is much greaterthan that reflected from a darkersurface, and accordingly the sun pro-vides greater illumination in theArctic than in other regions. Whenthe sun is shining, sufficient light isreflected from the snow almost toeliminate shadows except in polarareas where the shadows are quitelong when the sun is shining. Thiscauses a lack of contrast, making itdifficult for the observer to distin-guish the outlines of objects even atshort distances. The landscape mayappear as a featureless grayish-whitefield. Dark mountains in the distancemay be recognized but a crevasse im-mediately in front of a mountain maybe undetected because of the absence

41


of contrast. There is good illumina-tion from a full moon, and even thestars create considerable illumination.Only during periods of heavy over-cast does the arctic night approachthe darkness of other regions. A fogcondition peculiar to the arctic cli-mate is ice fog. This is composed ofminute ice crystals instead of thewater droplets of ordinary fog. Ice fogforms in very cold, still air in a shal-low layer next to the ground. It isalmost always present at temper-atures of -45°F to -50°F in the vi-cinity of a source of water vapor andremains as long as these conditionspersist. Where the smoke from build-ing chimneys contributes water vaporto cold, still air, ice fog may form attemperatures as high as -200 F.When the temperature increasesrather than decreases with heightthrough a layer of air, it is termed aninversion. The strong temperature in-versions present over the Arctic dur-ing winter cause several phenomenathat affect observation. Sound tendsto carry great distances. Light raysare bent as they pass through the in-version at low angles, often causingobjects beyond the horizon to appearabove it. This effect, termed looming,is a form of mirage.

(2) Fields of fire. The fields of fire ofautomatic weapons are subject to theeffects of wind and snow and the finalprotective line fires may be renderedineffective by snow drifts. Impactbursts of high trajectory light artil-lery, mortar, and hand grenade firesare rendered relatively ineffective bythe cushioning effect of deep snow;heavy artillery, however, remainshighly effective. The employment ofproximity or mechanically timed airbursts and overhead fire usually isadvisable. Because of the lack of iden-tifying objects and landmarks onsnow-covered terrain, the adjustmentof fire is difficult. Registration firewith air observation and by soundand flash is hampered, since the snow

obscures projectiles and bursts. Around bursting on impact in deepsnow appears as a small white splash,making sensing extremely difficult.Because of the cushioning effects ofthe snow, mines may fail to detonate.The clear air and snow cover mayincrease the thermal radiation effectof nuclear detonations in flat terrainand snow shelters will be vulnerableto blast effects. Heavy snow and hard-to-maneuver terrain will slow troopsin traversing areas contaminated byinduced and residual nuclear radia-tion. When used in deep snow, im-pact-detonating chemical ammunitionburns in the snow and the chemicalagent tends to be smothered by thesnow. Toxic chemical munitions pro-duce less vapor concentration becauseof the low temperature and thesmothering effect of the snow. On theother hand, low temperatures increasethe persistency of toxic chemicalagents in both vapor and liquid form.Decay of biological agents is not asrapid in arctic areas as it is in tem-perate or tropical areas.

e. Cover and Concealment. The snow-coveredterrain offers few features that provide ade-quate concealment and cover. Tracks in thesnow are almost impossible to hide, and dirton fresh snow can be observed at a great dis-tance. Due to the high visibility, effectivecamouflage is difficult. Because of the difficul-ties of concealment, night movements arefrequently advisable.

f. Obstacles. During the winter months, thelakes, swamps, and rivers are frozen over andcannot be employed as natural obstacles. Arti-ficial obstacles may be devised by freezinglarge masses of snow or icecrete (a densefrozen mixture of water, sand, and sometimes,gravel) into desired shapes, or by icing deepdrifts. Roadblocks may be made by icing asection of the road, preferably one which theenemy must approach on an upgrade. Tanktraps may be devised by cutting the ice on alake or river, then allowing it to refreezeslightly.

g. Avenues of Approach. Winter is generallythe best time to travel in the Arctic and sub-

42


arctic, since the lakes, streams, and muskeg 100 centimeters (40 inches) deep without theareas are frozen over. Frozen rivers and waterways often become the best routes of advanceand lines of communications during the wintermonths. In general, most vehicles are immo-bilized in snow from 1 to 1.5 meters (3 to 5feet) deep. The consistency of the snow,whether it is dry and loose, moist, or packed,affects the mobility of vehicles to a great ex-tent. Tracked vehicles usually can move at lowspeeds in packed snow that is no more than 1meter (3 feet) deep. After a packed snow trailhas been formed by the passage of severalheavy vehicles, normal speeds may be main-tained. A thaw or the passage of a great manyvehicles on a relatively warm day will melt thesnow surface, resulting in a coating of glareice. The road then becomes practically impass-able to tracked vehicles unless ice cleats areinstalled on the tracks or the road is sanded.Foot movements are slow in 50 centimeters (20inches) of snow and impossible in more than

use of snowshoes and skis. Hard-packed snow,however, is not difficult for troops to negotiate.With reasonable care lakes and streams maybe crossed by vehicles in winter. The ice firstmust be checked for thin spots, cracks, andpressure ridges. During the spring thaws,movement in ice and snow across tundra isdifficult and dangerous and cross-countrymovement is practically impossible. After thesnow cover has melted from the ground, bothwheeled and tracked vehicles can move rela-tively freely on it as long as the surface re-mains frozen. This layer of ground that thawsin the summer and freezes again in the winteris termed the active layer. As soon as the activelayer has melted, the tundra cannot supportheavy concentrated loads and ordinary vehicleswill bog down. Even special-purpose vehiclesbecome roadbound during the thaw period andcannot move across the tundra.

43


CHAPTER 5

NATURAL TERRAIN FEATURES

Section I. SIGNIFICANCE

51. Definitionsa. Topography. Topography refers to the

physical features, both natural and manmade,of the earth's surface. In terrain analysis, thefollowing categories of topographical featuresare considered: relief, drainage, surface mate-rials, vegetation, special physical phenomena,and manmade (cultural) features. Terrain re-fers to a consideration of topography in termsof military significance. Weathering and ero-sion play a major role in shaping natural fea-tures (fig. 13). Weathering comprises the ef-fects of the weather elements and erosionincludes the action of running water, waves,moving ice and snow, and wind upon rock andsoil.

b. Landforms. Landforms are the physicalexpression of the land surface. The principalgroups of landforms are plains, plateaus, hills,and mountains. Within each of these groupsthere are surface features of a smaller size,such as flat lowlands and valleys. Each typeresults from the interaction of earth processes

in a region with given conditions as to climateand as to kind and structure of rock. The indi-cations of relative elevations given are to af-ford specific definitions for the purposes of thismanual. Other distinctions may be found inother references. A complete study of a land-form includes determination of its size, shape,arrangement, surface configuration, and rela-tionship to the surrounding area.

c. Relief. Relief refers to the irregularities ofthe land surface. Local relief indicates the dif-ference in elevation between the highest andlowest points in a limited area and the size ofthis area depends upon the purpose for whichthe surface is being considered. In terrainstudies, it is usually five square miles. Relieffeatures are the individual forms of the landsurface, such as hills or ridges and major re-lief features are plains, plateaus, hills andmountains. Minor relief features include:

(1) High ground-swells, knolls, mounds,knobs, hummocks, hillocks, spurs,ridges, buttes, mesas, and dunes.

Figure 15. Landforins caused by erosion in arid climate (a) Pinnacle. (b) Butte (Grand Canyon, Arizona).

44


(2) Depressions-gullies, draws, gulches,wadis, ravines, gorges, arroyos, can-yons, and basins.

(3) Breaks in high ground-saddles,notches, cols, passes, cuts, and gaps.

(4) Special features-alluvial fans, talusslopes, talus cones, and boulder fields.

52. Military Operationsa. Influences. Terrain influences strategy and

tactics. What aspects of the terrain are mostimportant at any given time will depend uponthe particular requirements of the commandconcerned. Logistic requirements, for example,may emphasize the importance of communica-tion centers, routes and rail nets, and water-ways. The tactics of a large-scale campaignmay be dictated chiefly by the barriers im-posed by major rivers and lakes, mountains,forests, or swamps.

b. Attack. In the attack, the correct use ofterrain increases fire effect and diminisheslosses. Dominant terrain forms the frameworkof the system of observation, which in turndirectly determines the effectiveness of sup-porting weapons, the disposition and control ofthe attacking forces, the selection of objec-tives, and protective measures. Broken terrain,dense woods, built-up areas, and abruptchanges in elevation hinder the offensive em-ployment of armor but afford cover and con-cealment for infantry. Open, rolling terrain,although providing little cover and conceal-ment for infantry, is suitable for rapid ad-vances by armored formations. Soil traffic-ability may be a determining factor in select-ing type of attack or an avenue of approach.

c. Defense. The nature of the terrain is a

major factor influencing the commander whendeciding upon position defense or a mobiledefense. When the terrain restricts the abilityof an attacking enemy to maneuver and pro-vides natural lines of resistance, a position de-fense may be desirable and of course, terrainthat facilitates maneuver by defending forceswill favor a mobile type of defense. In selectingthe key areas for defense, the commander de-pends largely upon a terrain study. In addition,a terrain study frequently will give valuableindications of probable enemy assembly areas,field and air defense, artillery positions, ob-servation posts, and avenues of approach.

d. Retrograde. In retrograde, good observa-tion and fields of fire permit engagement ofthe enemy at long ranges. Natural and arti-ficial obstacles are exploited to strengthen de-fenses, protect exposed flanks, and impede theenemy advance. Concealment and cover areessential for assembly areas and routes ofmovement. Road nets are exploited to expeditethe movement of friendly forces and to facili-tate control, and are denied to the enemy forthe same reasons. The effects of weather onthe terrain influence observation, trafficability,control, and the performance of troops andequipment.

e. Nuclear. The maximum effects of a nu-clear weapon are subject to many variables, de-pending on how the weapon is employed. Blastand thermal effects would extend to a greaterdistance in open terrain, but the missile effectand thermal fires obtained with a certainheight of burst could create many adverse con-ditions, such as tree blowdown, induced radia-tion, and immediate residual radiation.

Section II. LANDFORMS

53. Plainsa. Definitions. As a landform group, plains

are generally flat to rolling areas with uplandsor interstream areas less than 150 meters (500feet) above adjacent valley bottoms. A dissectedplain is one with a surface that is interruptedby erosional features, and an undissected plainis one with a smooth uninterrupted surface.

b. General Characteristics. Plains may besituated at any elevation. Some are thousands

of feet above sea level and others are at sealevel. Some are rough and rolling and othersare flat. Because of their low degree of localrelief, plains generally have low angles ofslope. In temperate climates, this characteris-tic makes them favorable for transportationroutes. Where there is monsoon weather or atropical climate, however, more reliable routesmay be provided by higher terrain. The detailsof relief include uplands and lowlands, ridges

45


and valleys, and hills and hollows, all within c. Classification. Plains are classified as-local ranges of elevation of 150 meters (500feet) or less.

(1) Flat. Local relief of less than 15 me-ters (50 feet).

Figure 14. Coastal plain formed by volcanic lava (Hawaii).

I - I-

Figure 15. Outer delta features (Moses Point, Alaska).

46

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47


(2) Undulating. Local relief of 15 to 45 Cuestaform coastal plains are characterized bymeters (50 to 150 feet).

(3) Rolling. Local relief of 45 to 90 me-ters (150 to 300 feet).

(4) Roughly dissected. Local relief of 90to 150 meters (300 to 500 feet).

(5) Slope. In terms of slope, plains areconsidered smooth when they havelarge areas with a slope of less than2 percent, and rough when there arelarge areas with a slope of more than2 percent or many small areas withsteep slopes.

d. Coastal Plains. These are generally lowand featureless (fig. 14). Frequently they haveshallow valleys formed by streams that origi-nate inland. Swamps usually are numerous.

long, low ridges alternating with lowlands inbands several miles wide and many miles longgenerally parallel to the coast. The ridges onthis 'type plain are usually asymmetrical, thesteeper slope being inland.

e. Delta Plains. These plains, which areformed by sediments deposited at the mouthsof streams and rivers, are usually low andmarshy, with a local relief of less than 15 me-ters (50 feet) (fig. 15). The features of great-est relief are the natural levees, which are low,broad banks of alluvium on either side of thestream channels. For protection against streamoverflow, artificial levees may be built near thestream on top of the natural levees.

f. Flood Plains (fig. 16). These, also called

Figure 17. Meandering river, showing flood plain and oxbow lakes.

48


OLD ALLUVIAL PLAINNOW EXISTING AS A

TERRACEOXBOW LAKE

FILLED MEANDERCHANNEL

SURROUNDINGHIGHLANDS

ALLVIAL /FAN

Figure 18. Flood plain with evidence of pre-ezisting meander.

alluvial plains, are formed by weathered anderoded material deposited by streams upon thefloors of their valleys. The flood plain usuallyis poorly drained, and may contain marshes,swamps, lakes, and former stream channels.Unless protected by levees, it may become part-ly or completely covered by water in times offlood. The surface is flat, the levees alternatingwith swamp areas. Meandering rivers andcrescent-shaped (oxbow) lakes are characteris-tic of this type plain (fig. 17 and 18). The siltsand clays deposited on flood plains make pro-ductive soils, and this type plain is used ex-tensively for agriculture.

g. Piedmont Plains. These are alluvial plainsformed by mountain streams with steepgradients that deposit a sediment, consistinglargely of gravel and sand, at the point wherethe stream enters the lowlands. This type ofplain is found in arid and semiarid regionswith meager vegetation and torrential rains.Although the plain may appear level, actuallyit slopes away from the mountain base. Manypiedmont alluvial plains are covered only withshrubs or sparse grasses. Those with fine soilsare high in mineral plant fodds and, if irriga-tion water is available, they are suitable foragriculture.

h. Glacial Plains. These (fig. 19 and 20)

are classified as either ice scoured or driftplains.

(1) Ice-scoured plains are level to gentlyrolling areas composed largely of barerock. They are characterized by round.ed rock hills and broad open valleysand basins with comparatively lowlocal relief. Over the valley floorsthere may be a thin covering of glacialdebris which serves as an anchoragefor shallow-rooted trees, chiefly coni-fers. There are numerous falls, rapids,and lakes. Some small shallow lakesbecome filled with remains of marshvegetation, such as sphagnum moss,creating bogs of the type calledmuskeg in Canada.

(2) Drift plains consist largely of boul-ders, gravel, sand, or clay in layers ofvarying thickness on top of otherstrata of rock and soil. The principalcharacteristic is a gently undulatingsurface which includes broad, lowhills, or swells, and wide, shallow de-pressions, or swales. Commonly thelocal relief is less than 30 meters (100feet). Large areas of drift plains areessentially flat, with poorly developednatural drainage. Although soils aregenerally heterogeneous mixtures,

49


Figure 19. Glacial plain (Moose Jaw, Saskatchewan, Canada).

areas of impervious clays are com-mon. After heavy rains, ponds severalacres in extent may form; and unlessartifically drained, the water maystand until it evaporates. In some lo-calities there are hills of clayey tillcalled drumlins (fig. 21) that occa-sionally reach heights of more than30 meters (100 feet) and may be amile long. Streams in this type ofplain may be interrupted by swamps,lakes, falls, or rapids.

i. Lacustrine Plains. These are formed bysediment settling on lake bottoms. Subsequent-ly the lake was drained by natural forces, orevaporated because of a major change in cli-mate. They are level and often contain salty oralkaline lakes. Generally they are character-ized by poor drainage and alkaline soils.

j. Loess Plains. These are formed by wind-blown particles of silt, called loess, which havebeen deposited over large areas, forming asmooth, gently sloping surface. The ability ofloess to stand in vertical walls results in steepescarpments along gullies, stream valleys, andartificial cuts (fig. 22).

k. Karst Plains. These (fig. 23) are a typeof erosional plain developed on limestone. Theyhave a pitted surface along with exposed bed-ding plain edges (pinnacles) tilted through thesurface. The pitting is formed from subsurfacecollapsing due to the solvent action of under-ground water. Between the depressions there

are low, irregular ridges or hillocks. Numerouscaverns are formed beneath the surface of akarst plain, and there are also large under-ground streams which may issue at the surfaceas springs of considerable volume.

54. Plateausa. Description. A plateau is commonly bor-

dered by an escarpment or steep slope on atleast one side. The plateau surface may be cutby deep, narrow stream valleys, but the inter-stream areas are mostly broad and nearly level.Tabular uplands with a local relief of morethan 150 meters (500 feet) may be consideredplateaus. They vary greatly in configuration,but most have broad flat surfaces high abovesea level, and are deeply trenched by narrowvalleys. Depending upon the stage of the ero-sion cycle, the valleys that dissect the plateaumay be widely spaced early in the cycle or veryclosely spaced late in the cycle (fig. 24). Mostlarge plateaus are in regions with arid or semi-arid climates. Plateaus may be classified intothree major types:

(1) Intermountain (fig. 25). Surroundedor nearly surrounded by mountains.

(2) Piedmont. Lying between mountainsand plains, or between mountains andthe sea.

(3) Continental (fig. 26). Rising abruptlyfrom bordering lowlands or the seaon most or all margins; usually with-out conspicuous mountain rims.

50


I:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~I

kl- X:,~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

51


Figure 21. Drumlin (New York).

b. Climates. In arid climates, streams usual-ly flow in canyons cut into the plateau, thetypical canyon having a narrow bottom offer-ing little space for a roadway. The stream isseldom navigable and follows a steep, boulder-strewn course interrupted by rapids and falls.Sudden and extensive changes in stream levelare common. Canyons usually are too deep tobe crossed easily and too wide to be bridgedeconomically. They rarely provide a transpor-tation route and are a difficult obstacle tomovement. Areas between the streams usuallyare flat or rolling uplands, some of vast extent.Areas of interior drainage called bolsons existon some plateaus. The streams empty intothese, resulting in level areas that may containlarge salt lakes or salt marshes. Plateaus inhumid climates tend to be more dissected bystream erosion than those in arid climates.Broad divides with rounded and irregular up-lands are common.

c. Ice Plateaus. The vast sheets of ice thatcover most of Greenland and Antarctica maybe regarded as great plateaus. Greenland isan intermontane plateau, surrounded by afringe of mountains. In most of Antarctica,the ice rises in a sheer wall, then slopes uprapidly to a fairly level interior with an aver-age elevation of about 1,830 meters (6,000feet), the maximum elevation of 3,050 meters(10,000 feet) being found in regions inlandfrom the Pacific coast. In general, the surfacesof an ice plateau are flat or have parallelridges a few feet in height which result pri-marily from the wind and drifting snow.

(1) Marginal features of Greenland. Thehighland or mountainous rim and thehigher summer temperatures of

Greenland produce marginal featureswhich are different from those ofAntarctica. The ice is confined by thehighlands, melting some distance in-land on the southern and westernmargins. Where ice does not dischargeinto the sea, it protrudes through gapsin the bordering highlands (fig. 27).Irregular icebergs form, drifting intothe Atlantic Ocean during the springmonths.

(2) Marginal features of Antarctica. Themarginal ice of Antarctica is thin andtraversed by deep cracks. Except ina few localities where it is retainedby the fringing mountains, the iceoverruns the land margins, so that theexact position of the continentalshoreline is not known. The edge ofthe ice is marked by sheer cliffs. Fromthese cliffs giant icebergs split offalong crevasses as a result of under-cutting by waves and the buoyant ef-fect of sea water. Some of these aretens of square miles in area. The ice-bergs disintegrate by melting anddisperse as masses of floe and driftice which fringe the continent formany miles.

55. Military Effects of Plains and Plateausa. Variety. Although plains and plateaus are

characterized by relatively low relief comparedto hills and mountains, they present a widevariety of topographical conditions. Sinceeach type of plain or plateau differs in its fea-tures and effects, one can only generalize abouttheir influences on military operations.

52


co

i~~~~~~~~~~~~l

I , 5

i'·1`U1177+-CI~~~N~ll5


~;i~i~"9ti Ar.

Figure 23. Karat plain (Canada).

Fi- ai I.S

jB~~~~i;.r, , ,~~~~~~~~

--waif ~~~4_~

Figure 24. Plateau dissected by stream (Deschutes River, Oregon).

b. Movement.(1) Coastal plains. In general, the topog-

raphy of coastal plains offers no ma-jor obstacle to the cro,ss-countrymovement of tracked vehicles, al-though there may be areas that aredifficult or impracticable because of

unfavorable soil conditions and densevegetation in areas of medium toheavy rainfall. Movement along anindented shore usually is difficult be-cause the terrain is separated intocompartments by streams and estu-aries. Cross-country movement in-

54


__ - n _

~~' ~~ 7 !", Z 'W~~;

2. C

Figure 25. Intermnountain plateau (Jackson Hole, Wyoming).

land may be limited to narrow areasbordered by water. In such terrain,attacks may require amphibious sup-port. Coasts with beach ridges hinderan advance inland because vehiclesmust cross poorly drained areas be-tween relatively stable sand ridges.Terrain of this type impedes the ade-quate dispersal of troops and supplies.

(2) Delta plains. On delta plains cross-country movement usually is hinderedby marshy ground, shifting streamswith loose sand and mud bottoms,and thick vegetation. Soils are betterdrained in the inner regions of thedelta. Normally the natural levees ofstreams provide the highest, best-drained, and most trafficable parts ofthe delta. Movement on the low-lyinggrounds of delta plains is alwaysthreatened by the possibility that theenemy will destroy dikes or levees andflood the area. The use of waterways

as avenues of approach by the enemymust not be overlooked.

(3) Alluvial Plains. The stream valleys inalluvial plains generally provide cor-ridors through areas of greater relief.In dry weather, the cross-countrymovement conditions usually are ex-cellent, except for such obstacles asstreams and local areas of unfavor-able soil or dense vegetation. In wetweather or during floods movementmay be limited to small areas ofhigher, better-drained ground, such aslevees. Alluvial terraces are aboveflood levels and may be well-drained,but they are commonly isolated bysteep slopes. It is not unusual for astream to meander from one side ofits valley to the other. If the valleyslopes are steep, such meanderingmay eliminate vehicular movementup or down the valley.

(4) Glacial plains. The topography of

55

I

f, 111), 1�el'4 t , 'I'4'i42p�


'Cur" X iRB . g'. Ija i·

;a* E *E ' He'' --- '-i

W _ nj4 _>

Figure 26. Eroded continental plateau (Grand Canyon, Arizona).

glacial plains usually presents no in-surmountable obstacles to movement.Large boulders may be obstacles insome area. In regions containing largeareas of soft ground, lakes, ormarshes, movement in the rainy sea-son may be greatly hindered by mud(fig. 28).

(5) Lacustrine plains. No topographic ob-stacles to movement are offered by the

level surface of lacustrine plains (oldlake beds). During wet weather,however, the fine soils may be slow-drying and become nontrafficable(fig. 29).

(6) Loess plains. Loess is a fine-grained,yellowish-brown silt deposited by thewind. In dry weather, movement con-ditions on loess plains are good, ex-cept where escarpments and ravines

56


,,I *I.T( Pag ,-r - W0

Figure 27. Tongues of icecap descending toward fiord (Greenland).

are encountered. Ground conditionsmay become very poor in wetweather, making cross-country move-ment impracticable.

(7) Karst plains. Movement on karstplains, a limestone region, is limitedchiefly by the sinkholes, which mayhave steep slopes and contain swampsand ponds. In wet weather the clayeyresidual soil overlying the limestonemay limit movement in some areas.Karst regions vary greatly in theircharacteristics-from a plain with anoccasional sinkhole to a surface sopitted and broken as to make evendismounted movement very difficult.Knowledge of the erosional develop-ment is necessary to evaluate such anarea properly.

c. Observation. The degree of observationavailable on coastal plains is normally goodalong the coastline, but inland the flat countryand forest cover usually offer few observationpoints. Observation is limited on delta plainsbecause the low, level ground generally is cov-ered thickly by vegetation. On alluvial plains,observation from the valley bottoms usually ispoor, but the bordering regions provide com-manding views into the valleys. Where vegeta-

tion does not interfere, it may be good on themore level portions of these plains. Vegetationalso determines the amount of observation thatmay be secured in lacustrine, loess, and karstplains.

d. Cover and Concealment. Coastal plainsprovide few areas with sufficient cover andconcealment for larger units. Except for thelevees, there are also few topographic featureson delta plains that will conceal or protecttroop bodies of any size. Little cover and con-cealment are available on alluvial plains, ex-cept for that provided along terraced scarps,river banks, and levees. On glacial plains, coveris lacking in the more level parts, but theremay be some limited cover and concealmentprovided by knobby and forested areas. Thesinkholes of karst plains also provide a moder-ate degree of concealment and cover.

e. Construction.

(1) Coastal plains. Although generallythere is no hard rock on coastal plains,sand and gravel are abundant onbeaches and along streams. Theground of coastal plains is excavatedeasily, but the depth of excavationusually is limited by the high watertable. Long and straight road aline-

57

e· -r


Figure 28. Glacial boulders (Yo8emite National Park).

ments normally can be obtained.There are many suitable sites for air-fields, particularly along the marineterraces.

(2) Delta plains. Abundant sand and finebinder material may be obtained ondelta plains, but gravel is scarce.There are no exposed hard-rock for-mations or bedrock. Generally thelocation of airfields and roads mustbe confined to the levees. Structuralfoundations not built upon levees areunreliable, and may settle due to thelow, poorly-drained ground with athreat of periodic flooding. Drainagealways is a serious problem becausethe levees prevent the return of sur-face water to the river, and the high

water table limits underground re-turn. Accordingly, drainage andpumping systems may be required.

(3) Alluvial plains. Rock is scarce in floodplains except where it may crop outalong the scarps of terraces. Sand,gravel, and binder material are abun-dant along stream channels and theterrace scarps. Terraces also may pro-vide suitable sites for bunkers andunderground installations. Excava-tions in flood plains are limited bythe high water table, but these plainsand terraces if well-drained are suit-able for the construction of roads andairfields.

(4) Glacial plains. Sand and gravel are

58


7i0

t0P.

I.

r

10

.-

e

0;

I

k

59


widely distributed on glacial plains,and rock usually is abundant. On tillplains, boulders may provide buildingstone, but there is bedrock only in afew locations, such as in deep valleyswhere the overlying till has been cutthrough. Wet ground and weak soilsmay create foundation problemswhere the drainage is not good.

(5) Lacustrine plains. Except at the mar-ginal slopes, where sand, gravel, androck may be obtainable, lacustrineplains usually can provide only clayand fine sand for construction pur-poses. The fine-grained soil makes apoor foundation for structures, par-ticularly in humid climates. Lacus-trine plains provide level sites for air-fields with few natural obstructionsand allow unrestricted road aline-ments.

(6) Loess plains. Loess plains are a poorsource of gravel or rock, except wherethere are underlying deposits. Foun-dations require stabilization and incold climates the loess may heave. Indry climates, thick Ioess deposits areeasily excavated and are well suitedfor underground installations. Manygood airfield sites and road alinementsusually are available.

(7) Karst plains. Large quantities oflimestone for building stone andcrushed rock may be obtained onkarst plains. Sand and gravel usuallyare lacking. Excavation often is dif-ficult because of the irregular rocksurface, with deep clay-filled pits, andthe high pinnacles of rock that lie be-neath the residual soil. Grading usu-ally requires the excavation of rock.There is always a possibility of foun-dation subsidence.

56. Information Requirements - Plains andPlateaus

a. Plains.

(1) Extent of area covered by plain.(2) Surface (elevation, slope, kind of sur-

face).

(3) Major interruptions (hills, moun-tains, river valleys).

(4) Minor interruptions (gullies, sinks,levees).

b. Plateaus.

(1) Area covered by plateau.

(2) Surface (elevation, slope, surface, re-lief features).

(3) Major interruptions (hills, moun-tains, canyons, valleys).

(4) Margins (mountains above plateau,abrupt descending cliffs).

57. Mountains

a. Description. As a landform group, moun-tains are rugged areas with crests that are,in general, more than 600 meters (2,000 feet)above adjacent lowlands. They are commonlydistinguished from other major relief featuresby the predominance of slopes and their overallmassiveness. In terms of local relief, moun-tains may be classified as low when they havea local relief of 900 meters (3,000 feet) orless, and high when their height exceeds thatfigure. According to their size and arrange-ment, mountain features may be classified aspeaks, ranges, chains, and cordilleras.

b. Peaks. A peak is a conical high mass, thatrises above its surroundings. Ordinarily a peakis a feature of minor order upon a range, butas in the case of an isolated volcanic cone, onepeak may stand alone and comprise the entiremountain mass.

c. Ranges. A range is an arrangement,usually linear, of many peaks, ridges, andtheir valleys. The term ordinarily applies tomountains that have a general unity of form,structure, and geologic age.

d. Mountain Chain. A mountain chain con-sists of several associated ranges, usually moreor less parallel, having unity of position, formor structure, but separated by trenches orbasins.

e. Cordillera. A cordillera is a large regionalgrouping of mountain chains.

60


58. Mountain Features

a. Relief. Mountains are distinguished fromhills by their greater relief, more rugged con-tours, and more complicated surface patterns.The average slope of large mountains seldomis more than 20 ° to 25 ° from the horizontal,and only a few have slopes of more than 35 °

near the summit. Even walls that seem verticalseldom have slopes that average more than 70 ° .

b. Valleys. Except where they have reachedgrade level and meander in flat alluvial valleys,mountain streams have high gradients andflows of high velocity. The rapid downwardcutting action of the stream may uncover bed-rock of unequal hardness, so that falls andrapids develop. Some streams, in cuttingthrough bedrock of unequal resistance, erodevalleys which are broad at their headwaters,then narrow to gorges, and subsequently openout again downstream. Valleys formed byglacial action have wide rounded bottoms andsteep sides. They have U-shaped profiles, incontrast to the V-shaped profile of a streameroded valley. The walls are steep and rugged.Most glaciated valleys have one or more basinsin which impounded drainage creates lakes,ponds, or marshes.

c. Divides. Between the mountain valleysthere are uplands formed by remnants of theoriginal elevation. Rainfall on these uplandsseparates according to the surface slopes anddescends by numerous rivulets into adjacentvalleys, modeling the uplands as it flows. Theuplands are called divides. When they separatethe drainage destined for opposite sides of acontinent they are termed continental divides.

d. Foothills and Spurs. The lowest and leastmassive features of mountain uplands are thefoothills and spurs that fringe the principalhighlands. Foothills are hills located at thebase of higher mountains or hills. A spur is aridge projecting laterally from the main crestof a hill or mountain.

e. Passes. The erosion by streams or glacierscreates saddle shaped notches, or passes, in amountain barrier. The term pass is applied toany type of natural passageway through high,difficult terrain.

As a broad landform group, hills are roughareas with crests generally from 150 to 600meters (500 to 2,000 feet) above adjacent low-lands. They usually contain a predominance ofmoderate slopes. Hills may be classified aslow when they have local relief of from 150to 300 meters (500 to 1,000 feet), and high,when the local relief is from 300 to 600 meters(1,000 to 2,000 feet). Some very rough hillsmay appear mountainous in relation to adja-cent plains, and locally may be called moun-tains, but they are not properly of a size ornature to merit the term. Mature hill landsmay be almost entirely a succession of hills,valleys, and narrow ridges, with level land oc-cupying less than five percent of the total area.Hill regions in an early stage of erosion mayinclude some fairly level, plateaulike uplandsseparated by steep-sided valleys. Those in amore advanced erosional stage may have broadopen valleys and reduced slopes that are suit-able for agriculture. Because some of the slopesin hill regions are steep and untillable, theyhave retained their forest cover and havestreams with steep gradients that are capableof developing waterpower.

60. Military Effects of Hills and Mountainsa. Key Terrain Features. In both attack and

defense, the key terrain features may includethe heights which dominate valleys, the routesof communications, passes and valleys whichpermit cross-country movement through themountains, and aircraft landing areas. Domi-nating heights which may be used by theenemy for observation of avenues of approachmust be controlled.

b. Observation and Fields of Fire.

(1) Observation. In hilly and mountain-ous areas, observation may be re-stricted. In most cases, commandingheights provide only partial observa-tion of adjacent valleys and slopes.Foothills and spurs extending into avalley obscure observation along thevalley.

(2) Fields of fire. Mountains and hillsplace some restrictions upon the em-

61

59. HillsWWW.SURVIVALEBOOKS.COM

ployment of supporting weapons. Ar-mor loses much of its mobility becauseit cannot move across country. Occa-sionally tanks can be used in smallnumbers against limited objectives,but their action often is confined toproviding direct fire support. Artil-lery is effective, but the limited visi-bility in mountainous terrain restrictsobservation and adjustment of fire.Terrain features may also reduce theeffectiveness of air defense artilleryby making radar siting difficult andreducing the target acquisition rangeof the system. Survey and fire controlare hampered, and more time is re-quired for artillery to displace. Thereis difficulty in finding gun positionsthat do not have too much defilade.The heavier crew-served weapons ofthe infantry and their ammunitionare difficult to carry over the ruggedterrain. Mortars and recoilless riflesare effective and are favored for op-erations in mountains and hill regions.Deep valleys and ravines afford adegree of protection from the blasteffect of nuclear weapons when theaxis of the valley or ravine pointswell away from ground zero. When itdoes not, there is little or no shieldingeffect, and blast damage may be in-creased because the blast is canalized.Deep valleys and ravines afford sub-stantial protection from thermal andnuclear radiation to troops, materiel,and buildings located within theshaded portions. In terrain character-ized by deep valleys and ravines,however, blast effects of nuclearweapons may cause serious avalanchesand rock slides. Concentrations oftoxic chemical agent aerosols are ex-tremely hard to achieve on markeddownward slopes. Toxic chemicalagents and biological agent cloudstend to flow over rolling terrain anddown valleys, to remain in hollowsand on low ground and in depressions,but to go around obstacles. Localwinds, coming down valleys at night

or up valleys in the daytime, may de-flect the clouds or reverse the forecastflow; likewise they may produce fa-vorable conditions for cloud travel.

c. Cover and Concealment. The rugged to-pography of mountains offers abundant coverand concealment, although movement acrossslopes or crests above the timberline will beexposed. Sounds carry from valley bottoms tohilltops, but within the valley, sounds are muf-fled by ground forms and streams.

d. Obstacles. Major obstacles to movementinclude steep, high ridges and ranges, highvalley routes and escarpments, sloping cliffsand terrace faces. Minor obstacles includestream embankments, valley terraces andbenches, spurs, talus, and debris-choked valleys,and presence of boulders.

e. Avenues of Approach. Hills and moun-tains parallel to the axis of advance offer flankprotection, but limit lateral movement. Whenperpendicular to the axis, they are an obstacleto the attacker and an aid to the defender.Mountain roads must be improved because theroads are generally narrow, have steep grades,and poor surfaces. Sharp turns may preventthe use of trailers. Roads in valleys or alongdefiles require that the adjacent high groundbe secured to insure control of the roads.Mountain roads are subject to slides and maybe blocked by snow. Those on the crest ofridges may be exposed to enemy observation.Roads in defiles may be flooded and may alsohave large boulders. The best sites for militaryroads in mountain areas are normally on thesides of slopes.

f. Communications. Hills and mountains con-tain dead spaces that often limit the rangeand effectiveness of radios, although these re-strictions usually can be overcome by the useof relay sets. Wire laying is difficult, and visualsignals are not always dependable and oftencan be seen by the enemy.

g. Air Support. The hazards in mountainousregions place limitations upon the use of low-flying combat aviation. Targets are difficult tolocate and in many cases close air-supportstrikes must be controlled by aerial FAC's(Forward Air Controllers) or by indirect

62


means, since the functions of tactical air- mating the probable effect of fire on rockcontrol parties are hindered by the terrain andweather.

h. Combat. Combat in mountains and hillyareas usually consists of a series of independentactions to seize and hold key terrain, strikecommunication lines, and protect friendlyroutes of supply and evacuation. Infantry playsthe dominant role, since it is not roadboundand can close with the enemy under any con-dition of terrain. Commanding positions inmountain terrain are often rocky ridges oreminences with little or no soil. If the im-portance of the position justifies the time andeffort required, trenches, emplacements, andgalleries can be cut into the solid rock. Parapetsand breastworks of cobbles and boulders areeffective against small arms, but they arevulnerable to artillery fire. Log breastworksand protective shelters may be built if timberstands are conveniently located. Mines and ob-stacles find their most important use in ob-structing movement on roads and trails andthrough defiles. Roadblocks are effectivebecause of the difficulty of bypassing them.Mountain terrain favors the defender becauseavailable obstacles enable him to use minimumtroops to deny the attacker the use of existingroutes. He can force deployment of majorenemy units and the expenditure of largeamounts of mortar and artillery ammunition,and can inflict the maximum punishment fromprotected positions.

i. Construction. Hard rocks suitable for con-struction purposes are readily obtained in hillsand mountains. Sand is scarce, but gravel maybe secured in the lower stretches of streamswhere they approach the foot of the mountainsor flow through hills. There are few suitablelocations for airfields because of the difficultyof excavation in rock, the obstructed and lim-ited approaches, the poor accessibility, and theturbulent air currents. Highways, railways,and tunnels are vulnerable in these areas.Geologic data may be useful in indicating rockconditions favorable to initiating rock slidesby bombing or artillery fire to block enemylines of communication. Geological informationwill also assist in selecting sites for gun em-placements and other fortifications, in esti-

fragmentation, and determining the possiblericochet effects of projectiles. The soil usuallyis thin or stony, with underlying bedrock, sothat it is difficult to construct field fortifica-tions. Geologic study will assist in selectingareas where excavations may be made and inchoosing the required explosives and equip-ment.

61. Information Requirements - Hills andMountains

a. Extent and Type of Mountains or Hills.

b. Ridge Crests.(1) Location and orientation.(2) Elevations (typical, highest, lowest).(3) Height above adjacent valley flats

(average, highest, lowest).(4) Pattern (lo n g straight, parallel

ridges; branchlike and crooked ridges;clusters of knobs and peaks).

(5) Skyline (flat-topped and broad, orknifelike).

c. Slopes.(1) Shape (convex, concave).(2) Angle, in percent or degrees

crest, middle, near base).(3) Minor relief features (rough

boulder fields and gullies).

d Valley Flats.

(near

lava,

(1) Location.(2) Width (of main and tributary val-

leys; average, widest, narrowest forboth categories).

(3) Pattern (long, straight, and parallelvalleys or branchlike and crookedvalleys).

(4) Transverse profile (degree of slopenear center and margin of valley).

(5) Longitudinal profile (degree of slopenear mouth and head of valley).

(6) Terraces (benchlands) along bordersof valley flats (number of terracesteps, width, continuity, elevation ofsteps one above another, slope be-tween terrace levels).

63


(7) Stream channels within valley(straight or meandering, bordered bybluffs, gentle downslopes, or naturallevees).

e. Intermontane Basins.

of steps above one another, slope be-tween terrace levels).

f. Passes.

I (1)(2)

(1) Location.

(2) Width (average, widest, narrowest).

(3) Shape (round, oval, long and narrow,irregular).

(4) Flat bottom lands (extent and loca-tion).

(5) Terraces (benchland) about bordersof flat bottom lands (number of ter-race steps, width, continuity, elevation

Location.Elevations (average, lowest, highest).

(3) Number of passes (distance betweenpasses).

(4) Gradients (near head of pass, down-slope).

(5) When closed by ice and snow.(6) Character of defile formed by pass and

approaches (width, length, characterof slopes).

(7) Routes over each pass.

Section III. DRAINAGE

62. Effects of Drainage

a. Description. The water features of an areacomprise its drainage. They include streamsand canals; drainage and irrigation ditches;lakes, marshes, and swamps; artificial bodiesof standing water such as reservoirs and ponds,as well as such subsurface outlets as springsand wells. The character of these drainage fea-tures is determined by precipitation, relief,surface runoff and ground-water flow, andvarious manmade improvements. Vegetationhas a major influence upon drainage. Densegrass and tree growth on slopes tend to slowup and absorb a considerable amount of therunoff, but slopes with few trees and sparsevegetation permit rapid runoff and the forma-tion of channels by erosion.

b. Catchment. A catchment basin or catch-ment area is the total area drained by astream or system of streams. All water featureswithin this area are related and are consideredas a whole. The limits of the drainage basinare marked by the topographic divide whichseparates it from neighboring drainage sys-tems. The amount of water reaching thestream, reservoir, or lake depends upon thesize of the area, the amount of precipitation,and evaporation and transpiration. The rate ofevaporation depends upon the temperature,vapor pressure, wind, and solar radiation.

c. Patterns. Drainage patterns (fig. 30)reflect the subsurface structure. They are ofthree major types--dendritic, trellis, and radialdefined as follows:

(1) A dendritic drainage pattern is atreelike arrangement of streams foundmost frequently in an area underlainby homogeneous rock.

(2) The trellis pattern results from theinfluence of tilted alternating strataof weak and resistant rocks. The re-sistant strata separate each stream,producing the overall trellis effect.

(3) The radial pattern has streams thatradiate from a central dome that lieswithin a relatively flat area.

63. Rivers and Streams

a. Perennial Stream. A perennial streamflows throughout the year. The regular flowmay result from a spring lake or a glacier atthe head which furnishes a constant supply ofwater, from direct precipitation of fairly con-stant quality, or because the beds are deepenough to be permanently below the fluctuatingupper level of the ground water or water table.

b. Intermittent Stream. An intermittentstream originates in a source of water thatfails periodically and is particularly common

64


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in semiarid regions with seasonal rain or snow- age net is centralized in interior basins. Therefall. Some streams are intermittent becausethey depend for supply upon the water tableand do not have beds deep enough to be inde-pendent of fluctuations in the table.

c. Ephemeral Stream. An ephemeral streamis temporary, depending upon infrequent rain-fall for supply.

d. Bottoms. Rivers and streams deepen theirbeds by erosion of the underlying rock. Asstream erosion continues, the velocity of thecurrent decreases, with a resulting decreasein down-cutting potential. Eventually, the cut-ting potential is balanced by the sediment loadcarried by the stream. Subsequently, unlessthere is a change in the topography of thecatchment basin, the stream alternates betweenbuild-up and cutting down. Differences in theload carried by the water at different points,in velocity caused by changes in grade, and inthe degree of hardness of the rock make thebeds uneven, producing gorges, cataracts, rap-ids, and potholes. Where streams have a highvelocity and flow over loose materials, the bot-toms commonly are rocky. In slow-movingwater, fine material such as silt and clay isdeposited, and the bottoms will be muddy.

e. Banks. As down-cutting potential de-creases, side-cutting begins and the riverwidens its bed or develops a curving course.As a rule, these curves will have steep bankson the outside and gentle, low banks on theinside. The conformation will vary with thecomposition of the bank, the velocity of thestream, and the kind of materials transportedby the stream. Swift streams in rough reliefcommonly cut deep channels with low banks.

f. Flooding. Some streams flood annually andothers infrequently. Floods may be caused byrapidly melting snow, by excessive precipita-tion and runoff, by ice jams, or by any com-bination of these. When a river is in flood, thevelocity of water is greater than normal, withthe fastest current in the main channel.

g. Desert Drainage. Arid climates have longdry periods with infrequent precipitation. Des-ert streams for this reason are irregular involume and duration of flow. Large areas ofmany deserts do not have streams flowing outof their immediate vicinity because the drain-

may be separate basins at different elevationsin each desert. Many large streams flow intodesert lakes that have no outlet, or disappearthrough evaporation and seepage into poroussurface material. Some streams encountered indeserts originate in humid regions, flow acrossthe arid land, and then continue their coursein another adjoining humid area. When pre-cipitation occurs in desert areas, it is likely tobe in cloudbursts that generate a tremendousrunoff as the water rushes down. Sheltered drywashes or wadis may become extremely dan-gerous locations for bivouacs, gun positions,and installations during these brief but violentfloods.

64. LakesSome lakes are formed by glacial action

creating a depression which subsequently fillswith water, by the damming of a river by iceor a moraine, or by water filling a naturaldepression as a glacier recedes. A stream maybe formed into a lake because of interferencewith its natural course by a lava flow, dam,or avalanche. Coastal lagoons frequently areformed by the deposition of silt or sand atthe mouth of a river. The crater of an extinctvolcano often collects water and becomes alake basin. Salt lakes occur when a lake is sopoorly drained that the minerals in the waterremain while the water evaporates. In lime-stone country, lakes caused by the filling ofdepressions of dissolved rocks are common.

65. Marshes and Swamps

a. Description. A swamp (fig. 31) is an areaof saturated ground dominated by trees andshrubs. A marsh (fig. 32) is an area of satu-rated ground dominated by grasslike aquaticplants. A bog is an area of soft, wet, spongyground consisting of peat which supportsmosses, low shrubs, and in some cases poorlydeveloped trees.

b. Formation. Swamps, marshes, and bogsare formed by the overflow of rivers, dams,flooding by tides, a lack of balance betweenrainfall and runoff or seepage, impervious sub-soil in level areas, or the spread of vegetationin lakes, particularly in oxbow lakes. They may

66


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Figure S2. Marsh (Foxholm, North Dakota).

be numerous on delta and flood plains, wheresurface water is not readily drained. Extensivemarshes and swamps are encountered on theplains of humid areas. In glaciated regions,marshes, bogs, and swamps are common.

66. Glaciersa. Description. A glacier is a thick mass of

ice that moves slowly on a land surface. Glaciersdepend on the receipt of an annual amount ofsnow, and form only where there is a carryoverof snow from one season to the next. Abundantprecipitation is more important than extremecold. The ice is formed by the crushing of snowflakes from the weight of new snowfalls andshortly altered to a loose aggregate of rounded

67


granules of ice. With deeper burial these come frozen tightly in the sides and bottomgranules are deformed, locally melted and re-frozen and recrystallized, to produce a solidmass of interlocking ice crystals. There aretwo types of glaciers: valley glaciers and con-tinental glaciers.

b. Valley Glacier. A valley glacier (fig. 33)begins in the summit areas of the high moun-tains. Patches of snow are converted into ice-fields. Those icefields at the heads of formerstream valleys may eventually become thickenough so that the ice begins to move down-ward following pre-existing stream valleys. Asthe glacier moves down the valley, rock frag-ments become plucked from the walls and be-

of the ice. These fragments abrade the wallslike a giant rasp. This abrasion scratches andpolishes the walls and straightens out the val-ley.by grinding away irregularities on oppositesides. Narrow "V" stream valleys are reamedout into much more even "U" shaped valleys.

c. Ice Front. The lower end of a glacier, orthe ice front, stands at that point where thesupply of ice from up the valley is just equalto the loss through melting and evaporation.If supply is greater than loss, the ice frontmoves down the valley; if loss exceeds supply,the ice front retreats.

Figure 33. Valley glacier (Alaskan coast. Kame terrace and outwash plain in right foreground).

d. Debris. Rock debris carried in or on theglacier may be dumped at the ice front whenthe ice melts. This material, called till, consistsof an unsorted mixture of rock powder, pebbles,cobblestone, and boulders. If the ice front re-mains stationary for a period of time, a ridgeof till, extending across the valley, is formed.This ridge is termed an end moraine.

e. Continental Glaciers. Continental glaciers,such as those covering most of Greenland andAntarctica, begin in one or more central areasof snow accumulation. The ice starts to moveoutward when it becomes so thick that thepull of gravity on the mass exceeds the strengthof the ice. No slope is required and in many

cases the centers of accumulation lie at lowelevations. Continental glaciers make extensivedeposits dumped directly from the ice. Endmoraines mark positions at which the glacieredge stood for some time. They are long ridgesor belts of low hills that extend across thecountry for many miles. Large areas on theglaciated side of the end moraines commonlyreceive a sheet of till plastered on the under-lying rock. This ground moraine or till sheetwas left behind as the heavily loaded ice sheetmelted away.

f. Meltwater. Streams of meltwater leavingan ice sheet may flow down valleys that leadaway from the glacial front. The material pre-

68


viously left from frozen ice is deposited along ing through openings in the rocks, the waterthe stream valleys in the form of valley trains.Where the land surface slopes evenly awayfrom the edge of the ice sheet, meltwaterstreams may spread over the coufitryside inbranching, braided patterns forming wide-spread outwash plains. Outwash plains arecomposed of relatively well-sorted, evenly bed-ded sand and gravel which may be many feetthick and cover many square miles.

67. Ground Watera. Hydrologic Cycle (fig. 34). Water evapo-

rated from the ocean is condensed into clouds,from which it falls to the earth as rain, snow,sleet, or hail. Part of this water runs off intolakes and streams, or is retained by the soil,passing into underlying rock formations. Mov-

issues at the surface as springs, streams, andlakes. Ultimately all the water that is precip-itated returns to the atmosphere by evapora-tion from water surface or from the foliageof vegetation. Some also is released from fo-liage by transpiration, the process by whicha plant transmits water through its tissues,discharging water vapor from its foliage.Although this hydrologic cycle is irregular andmay extend over a period of years, no wateris lost permanently from circulation, but astage of the cycle may be bypassed or inter-rupted. Rain falling upon a heavily forestedarea, for example, may return directly to theatmosphere by evaporation without goingthrough other stages of the normal naturalprocess.

Figure 84. The hydrologic cycle.

b. Water Table. When water fills the poresand crevices of the underlying rock, a zone ofsaturation results. This is ground water andthe top of the saturated zone is the ground-water table, or simply, the water table (fig. 35).The depth of the water table beneath the sur-face varies according to topography, structure

of the rock formations, amount of rainfall,and nature of the pore spaces in the soil orrock. Water stored below the water table isthe source of supply for springs and wells.If the water table intersects the land surface,as it may on the sides of valleys, the waterwill flow or seep out as gravity springs or seeps.

69


Figure S5. Water sources.

c. Springs and Seeps. Subsurface waterissuing at the surface as a spring has a distinctcurrent, flowing continuously or intermittentlyfrom a localized area. Water issuing as a seepemerges slowly over a large area, without anoticeable current. Springs and seeps are oftwo principal kinds: gravity and artesian.

(1) Gravity springs. Gravity springs andseeps are those in which the subsur-face water flows by gravity from ahigher point of intake to lower pointof issue. This may occur where thewater table comes near or intersectsthe surface of the ground, usuallyaround the margins of depressions,along the slopes of valleys, and at thefoot of alluvial fans. Another typeoccurs along an exposed contact be-tween the overlying pervious stratumand an underlying imperviousstratum. They may appear at almostany elevation aiong a slope.

(2) Artesian springs. Artesian springsoccur where confined subsurface water

acting under the influence of pressurefrom a higher water level is forcedto the surface of the ground. Fissuresin the rock, fault zones, and, in somecases, solution channels may serve asavenues along which water can moveto the surface. The water is generallyunder much hydrostatic pressure, andtherefore rises in the spring. Becauseof this rise, the spring or well isclassified as artesian. A well withenough pressure to bring the waterabove ground is called a flowing ar-tesian well. If the water rises only toan intermediate level, it is a nonflow-ing artesian well.

d. Circulation. Ground water is not staticbut moves slowly through openings in the rockand soil toward points of discharge. The rateof movement is controlled by gravity or hydro-static pressure (the pressure exerted by waterat a higher level) and by the capacity of therock or soil to transmit water, termed itspermeability. Climate governs the amount of

70


water that will be contributed to the surface. its width, depth, and velocity. Rivers more thanThe amount that will be absorbed depends uponthe amount of pore space, or the porosity ofthe ground.

68. Hydrological Effects on MilitaryOperations

a. Rivers. Wide, deep rivers with valleysthat offer concealment may provide good de-fensive areas. The employment of a river as aforward edge of battle area (FEBA), however,may also result in a frontage too wide foreffective defense and with many covered areasthat interfere with observation and fields offire. Marshy terrain and ditches or tributariesinterfere with lateral communications and themovement of reserves.

b. River Line. In the attack of a river line,the initial objectives are key terrain featuresthat could permit the enemy to bring effectivesmall-arms fire on the crossing area. Next arefeatures that allow the enemy to deliver ob-served artillery fire, and, finally, those areason the enemy side of the river that are requiredto accommodate the troops, equipment, andinstallations necessary to prevent the enemyfrom delivering effective sustained artilleryfire. A river or stream may be a temporaryobstacle to cross-country movement, but it slowsdown advancing forces only until it is bridgedor assault boats can be brought to the site ora crossing by helicopter is effected. The effec-tiveness of a river as an obstacle increases with

150 meters (500 feet) in width are majorobstacles.

c. River Floods. Floods may cause longtraffic interruptions particularly by damagingtemporary bridges. A flood may immobilize atheater of operations unless an adequate systemof stream-gaging stations and flood-warningagencies has been established for all key rivers.Streams in mountainous areas are characterizedby a high velocity with considerable variationin their flow. While they may be effectiveobstacles during flood periods, they usually areso low in dry seasons that their beds may offerroutes of approach rather than obstacles tomovement. Such streams, however, are likelyto have beds so rocky as to eliminate vehicularmovement.

d. Lakes. Usually lakes are obstacles tomovement because few are narrow enough tobe bridged. They must be bypassed or crossedin amphibious vehicles or boats and where theyexist in chains or large groups, as in glaciatedareas, they become major obstacles (fig. 36).The narrow land corridors separating the lakescanalize troop movements and limit maneuver,rendering troops highly vulnerable to attack.A series of interconnected lakes may providean extensive communication system and mayalso include navigable rivers and canals as inFinland. An ice cover that is 1 meter (3 feet)or more in thickness will support heavy loads.Roads across frozen lakes may be prepared byclearing away the snow.

Figure s6. Arctic lake region (Northwest Canada).

71


e. Marches and Swamps. Normally movement bacterial pollution, seasonal varia-through a swamp or marsh is usually limitedto causeways, but many vehicles are now usedin swamps in what is known as a riverineoperation. These may be key terrain featuresthat could be seized by airborne, airmobile,or mechanized forces prior to a large-scalemovement. Mud and peat bottoms usually pre-vent cross-country movement. Special engineerfloating and portable bridging equipment maybe necessary to supplement other means oftraversing a swampy area or to cross or bypassa gap in a causeway. Snow roads may be builtover swamps by removing the snow and thenpouring water over the cleared surface untila frozen surface is obtained.

69. Information Requirements - DrainageMajor drainage areas are shown on maps of

appropriate size accompanying some terrainstudies. Textual notes are provided if the im-portant facts cannot be shown adequately ona map. Detailed information on features ofmilitary significance along a stream or portionsof it may be shown on a strip map or annotatedphotomosaic. Information may include-

a. Rivers and Streams.(1) Name or other identification, and

location.

(2) Channel characteristics (form (fig.37), length, profile, gradient of streambed).

(3) Bottom characteristics (composition,depth, firmness, unusual conditions).

(4) Flow characteristics.(a) Measurements and periods of oc-

currence at low, high, and meanwater of depth, width, volume ofdischarge, and velocity (minimum,maximum, and mean).

(b) Special phenomena (crosscurrents,undertows, eddies, floods) ; periods;area covered; destructive effects.Tidal effects at low, high, and meantides.

(5) Physical and chemical characteristicsof water (turbidity, color, odor, taste,temperature, chemical composition,

tions).(6) Bank characteristics (composition,

stability, height, and slope).(7) Regulatory structures (levees and

dams).(8) Islands, bars, shoals, and rapids

(name, size, surface roughness, eleva-tion, and pattern).

(9) Ice (earliest, latest, and mean freezingand breakup dates, extent of frozensurface; thickness of ice; carryingcapacity; and frequency and locationof ice jams).

(10) Kind and prevalence of animal andvegetable life.

(11) Type and location of crossings.(12) Utilization of watercourse (for water

supply, irrigation, disposal of waste).(13) Accessibility for military water sup-

ply (relation of road nets to potentialwater points, off-road approaches, in-take problems).

b. Lakes.

(1) Name or other identification, andlocation.

(2) Length, width, depth and surfacearea at low, high, and mean water;periods of occurrence of each.

(3) Gage locations and periods of record,zero gage elevations, mean and ex-treme gage heights and periods ofoccurrence.

(4) Shore characteristics (composition,stability, height, and slope).

(5) Physical and chemical characteristicsof water (turbidity, color, odor, taste,temperature, chemical composition,bacterial pollution, seasonal varia-tion).

(6) Bottom characteristics (composition,depth, and firmness of material, un-usual bottom conditions, profiles).

(7) Regulatory structures.(8) Islands, bars, and shoals (name, size,

surface roughness, elevation, andpattern).

72


Figure 37. Characteristic braided stream drainage pattern (Canada).

(9) Ice (earliest, latest and mean freezingand breakup dates; extent of frozensurface; type and thickness of ice;and carrying capacity).

(10) Kind and prevalence of animal andvegetable life.

(11) Type and location of crossings.

(12) Utilization of water body (for watersupply, irrigation, disposal of waste).

(13) Accessibility for military water sup-ply (relation of road nets to potential

water points, off-road approaches in-take problems).

c. Marshes and Swamps.(1) Information in b above, as applicable.(2) Seasonal variations (months when

variations in extent and wetness aregreatest and least).

(3) Cross-country movement under vari-ous seasonal conditions.

(4) Existing or potential causeways.(5) Special conditions (quicksand, per-

mafrost).

Section IV. NEARSHORE OCEANOGRAPHY

70. Beachesa. Description. A beach is defined as the

area extending from the shoreline inland to amarked change in physiographic form or ma-terial, or to the line of permanent vegetation(coastline). In amphibious operations, it isconsidered that portion of the shoreline desig-nated for landing a tactical organization.Beaches are characterized according to theirpredominant surface material, such as sand,silt, cobble, pebble, boulder, or by combinationsof these materials, such as sand and pebble.Mud beaches are common, but silt is not usuallyfound in beach form, occurring more commonlyin underwater banks and shoals. In general,beaches are long and continuous on low-lyingcoasts, or on shores with soft rock formations,

and where there is an abundant supply ofmaterial deposited by streams. Along hard-rockcoasts and on those not well supplied withstream-carried material, beaches are short anddiscontinuous, and are usually separated bybold headlands or rock outcrops (fig. 38).

b. Width. The width of a beach is subjectto considerable change. Where there are sea-sonal variations in wave attack and the supplyof material, beaches may disappear or be great-ly damaged when the wave attack is heaviest.Beaches formed principally by streams usuallyshow marked seasonal variations in width, andare widest during the period of least rainfall.Beach widths are most nearly constant whenthe beaches are protected by groins or similarstructures.

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c. Slope. The slope of a beach is determined g. Fresh Water. Fresh water is seldomchiefly by the size of the beach material andthe intensity of wave attack. Beaches of finesand that are not subject to intense wave actioncommonly have slopes ranging from 1 on 5 to1 on 60. Coarse material under light waveattack results in beach slopes from 1 on 5 to1 on 10. The band of wave uprush on a beachis a good indication of the slope. On air photo-graphs it may appear as a dark band lyingjust landward of the waterline. A wide uprushband indicates a flatter slope than a narrowband. On gravel beaches, however, uprushbands are always narrow, and usually do notappear clearly on aerial photographs.

d. Firmness. There is a wide variation infirmness between different beaches and differ-ent parts of the same beach. Beaches are mostfirm when damp and when the material size issmall. Dry sand usually is soft, except when thematerial size is small. Pebble, cobble, andboulder beaches are firm as far as bearingstrength is concerned but are loose, making itdifficult for tracked vehicles to cross them.Silt and clay are invariably soft, but combina-tions of mud and sand provide a hard surface.As a rule, exposed beaches are firmer thansimilar beaches in sheltered locations.

e. Vegetation. Vegetation immediately in rearof a beach is an indication of stability. Suchareas are firmer than other parts of the beachand always lie above the limit of wave uprush.There is no vegetation on gravel beaches, butbeaches composed of gravel and sand in com-bination may have a vegetation cover.

f. Assault Landing. Assault landing is basedupon the potential of the beach and hinterlandto permit the initial landing and the logisticalsupport for the operation. Attack transportships (APA) and attack cargo ships (AKA),which have a loaded draft of 8 meters (27 ft)and 7.3 meters (24 ft), respectively, requirelanding crafts for unloading. A landing shiptank (LST) requires a maximum draft of 4meters (13 ft), a landing craft medium (LCM)1.5 meters (5 ft), and a landing craft, utility(LCU) 2 meters (6.5 ft). Additional aid inlanding supplies and personnel include mobilepier sites such as the Spud Barge pier, bridgingand engineer equipment required to preparethe terrain for landing.

available on undeveloped beaches, although itmay be obtained from nearby streams or incompletely inclosed pools or lagoons that lieimmediately behind the beach. Streams orrivers with steep gradients that cross the beachwill provide fresh water at sites above thehighest reach of the tide.

71. Terrain Adjacent to Beachesa. Ridges. Beach ridges are mounds of beach

material heaped up by wave action along theupper limit of wave uprush as single ridgesor as a series of approximately parallel ridgesextending some distance inland. Commonlythese ridges reach from 1 to 2.5 meters (3 to8 feet) above mean high tide, but individualridges may be as high as 9 meters (30 feet).High ridges are found only in exposed locations,and are signs of occasionally severe storm waveaction. Ridges occur only when there is anabundant supply of material on or in back ofthe beach. In some locations belts of beachridges extend for 2 or 3 kilometers (a mile ortwo) inland, with a vertical difference in ele-vation of only a meter (few feet). Usually theseareas are covered with grass or low bushes.

b. Dunes. Dunes are formed by windblownsand carried inland from the beach and depos-ited as irregular hills or mounds. The sand is offine to medium size. Dunes may reach heightsof 90 meters (300 feet), although commonlythey do not exceed 30 meters (100 feet) inheight. Where there is vegetation, low bushes,and grass the dunes are fairly firm and can becrossed by light vehicles. Fresh water may beobtained from wells sunk in depression be-tween dunes (fig. 39).

72. Underwater Topographya. Description. An examination of the terrain

as shown in photographs, topographic maps,and hydrographic charts will indicate the prob-able characteristics of the hydrography. If theland behind the beach is flat and sandy ormarshy, the sea bottom close inshore also willbe fairly flat. A beach located on a longstretch of regular coastline normally will haveone or more sandbars offshore. Large rock out-crops along the beach or close inland indicatethat there are probably similar outcrops under-

75


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LONGITUDINAL

WIND

BARCHAN

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Figure 39. Windblown stationary dunes.

water near the shore. Beaches backed by cliffsor steeply rising hills generally will have afairly steep underwater gradient. The form ofthe beach also indicates the underwater con-tours. A wide, flat beach is an indication of agently sloping bottom offshore, and a sharpnarrow beach suggests a steep slope. Sandbeaches have flat to steep slopes, and beaches ofgravel, cobble, or boulders are usually steep.It must be remembered, however, that the

ATIONARY

entire beach profile is changeable, varying withthe wave conditions that act upon it. Shortconcave or pocket beaches (fig. 40) flanked bywell-developed headlands are the most constantin their form.

b. Bottoms. The characteristics of the mate-rials that comprise the nearshore bottom aresignificant in relation to their suitability forthe movement of men, vehicles, and landingcraft. Bearing strength and smoothness of grad-

76


Figure 40. Concave beach.

uations are the most important factors. Sand,sand and shell, and gravel bottoms are idealfor landing operations. They are firm andusually quite smooth, although bank, bar, andshoal formations are common. Sand and mudmixtures may be either firm or soft, but theyusually are smooth. Mixtures with a high per-centage of sand are firm, the firmness decreas-ing as the sand content is reduced. This type ofbottom often has soft spots that may provehazardous. Mud bottoms are generally avoided,since they are soft, smooth, and slippery. Anexception is the case of a thin mud cover over-lying a rock bottom, where the rock providesan underlying formation that will give asatisfactory bearing surface if the mud is notmore than a meter thick. Clay bottoms areunsatisfactory, since they are soft and slipperyand have little strength.

73. Coral Reefsa. Description. Reef-building corals are ma-

rine animals that remove lime from sea waterand deposit it around their living bodies,making hard structures of many types. Theydo not flourish at temperatures much under75° F. Consequently coral reefs are found onlyin tropical waters. Since corals cannot move,securing microscopic food from water movingaround them, they are usually found near theedge of reefs, along channels, and out fromheadlands. They cannot form opposite muddystreams or those with a heavy discharge. Ifthe water movement in coral areas is swiftenough, rounded coral heads will predominate,and in more quiet water there usually is an

open growth of branching corals. Reef coralscannot stand exposure to the air for more thana few hours, so that their upward growth islimited by the level of mean low water. Theybelong to one of three types-fringing reefs,barrier reefs, or atoll reefs (fig. 41).

b. Fringing. A fringing reef is attached tothe shore. If the wave attack is weak, therewill be a gently sloping beach of coral sand.Strong wave attack results in steep gravel,cobble, and boulder beaches. On most fringingreefs there are boat channels about 0.3 to 4.5meters (1 to 15 feet) deeper than the rest ofthe reef-flat, from 10 to 45 meters (10 to 50yards) or more wide, and more than a milein length. These run approximately parallel tothe land, opening into breaks in the reef, andproviding convenient waterways for smallcraft.

c. Barriers. Barrier reefs are locatedroughly parallel to the coastline at some dis-tance offshore. Whether or not a craft cancross a barrier reef depends upon the depthof the coral below water. Usually the coralsurface is about 15 centimeters (6 inches)above mean low water, but it may be deeper.Walking upon the reef is dangerous, sincethe reef-flat is seldom above water and theholes between coral colonies are irregularlyspaced, deep, and lined by jagged coral. At lowwater, extensions of the reef into the lagoonbehind it may create compartments that hinderor prevent the free movement of craft alongthe reef.

d. Atoll. Atoll reefs (fig. 42) are more or

77

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Figure 41. Barrier and fringing reefs--diagrammatic cross-sections.(A) Wide barrier reef.(B) Narrow exposed fringing reef.(C) Protected fringing reef. (Not drawn to scale.)

less rings of coral inclosing circular lagoons.The marginal zone of the reef is a strip from25 to 70 meters (25 to 75 yards) wide, acrosswhich a belt of surf moves with the rise andfall of the tide. If the outer, seaward slope ofthe reef is steep, there is a clear approach forlanding craft. A gentle slope will have coralheads growing just outside, making an ap-proach dangerous. At high tide it may be pos-sible to cross the marginal zone by boat. Reefislands usually are located on higher parts of anatoll reef. Typically these islands are surround-ed or partly surrounded by a beach 3 to 15meters (10 to 50 feet) or more wide, consistingof coral sand and organic debris. Reef islandsare seldom more than 3 to 4.5 meters (10 to 15feet) higher than the reef-flat, and their in-teriors usually are flat and featureless. From

the viewpoint of landing operations, the mostunfavorable feature is the high, surf-coveredmarginal zone. Surf intensity is less on theleeward side. On the lagoon side by enteringthrough channels or breaks in the reef, craftmay land on the sand beach at high water.Crossing the reef-flat at low tide is impracti-cable.

74. Military Considerations

a. Coastlines. A concave coastline is formedby a projection of water (bay or gulf) extend-ing into the coast. From the flanks, convergingfires may be brought upon landing forces. Theconvex type of shoreline includes gently out-curving shores, points, capes, and peninsulas.Supporting fires may be placed on the defender

78


Figure 42. Atoll reefs--diagrammatic cross section.(A) Open reef area.(B) Area of impermanent debris accumulation.(C) Reef-island area. (Not drawn to scale.)

from his flanks and, occasionally, from his rear.His routes of withdrawal or reinforcement arerestricted. It is difficult for the defender toorganize his fires and to secure extensive fieldsof fire. Convex shorelines are more exposed tocurrents, winds, and surf and are often steepand rocky, making landing difficult. A straightshoreline has no prominent indentations orpromontories. It offers no decisive advantageeither in attack or defense. Very few coast-lines, however, are so straight that provideno positions for flanking fires. An irregularcoastline is a complex of concave and convexshorelines.

b. Reefs. Barrier and atoll reefs may beobstacles at a distance from tlhe landing beach.A fringing reef forms a nearshore obstacle,

normally with a rough tablelike surface, thatextends seaward from the shoreline at a levelslightly above or below the water. A widefringing reef provides an area well suited tothe organization of defensive smallarms fires.

c. Offshore Islands. Frequently shorelinesare protected by groups of small islands lyingso close to the mainland that they form a com-plicated system of waterways immediately off-shore. Routes of approach to the mainlandthrough the islands may be tortuous and re-stricted, making an approaching landing forcehighly vulnerable throughout its shorewardmovement. These islands may be neutralizedwith nuclear weapons or may be isolated andreduced in detail by successive minor landingspreceding the main amphibious attack. Once

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secured, they provide the attacker with favor- tidal heights and surf, local peculiar-able artillery positions to support the landing.

75. Information Requirements - LandingAreas

Terrain studies made for planning amphi-bious operations are very detailed. Normallythey are based upon the complete data that isprovided by special studies and major sources.In general, the following items represent thefundamental information requirements relativeto a proposed landing area:

a. Location.

(1) For a beach 3 kilometers (2 miles) ormore in length, the latitude and longi-tude of its limits; for a beach lessthan 3 kilometers (2 miles) long, thecenter of the landing area is given.

(2) Nearness to objective of the opera-tions, if known, and to developed areassuch as water terminals, harbors, andadjacent beaches.

b. Sea Approach.

(1) Landmarks, both natural and man-made.

(2) Hydrography (nearshore and offshoredepths; flats (tidal or other), charac-ter of the material and its bearingstrength; length of and depths overreefs, bars, shoals, or other naturalobstructions; anchorage areas andtheir conditions; character of near-shore bottom material).

(3) Tides and currents (tidal rise andfall, local peculiarities, direction andmagnitudes of currents; neaps andsprings).

(4) Winds (strength, direction, effect on

ities).(5) Waves and surf (height and period

of offshore waves; intensity).

c. 'Beach.'(1) Material (type and size, firmness,

variability with weather or season,subsurface material).

(2) Gradient (note particularly scarpsand ledges).

(3) Beach structures (groins, bulkheads,jetties, submerged remains of formerstructures).

(4) Rivers and streams (variability inbeach character where rivers crossbeach; river channels).

(5) Effects of weather and duration ofdarkness and daylight.

(6) Local use of beach.(7) Sources of fresh water on or near

beach (both potable and nonpotable).

d. Terrain Inland or on Flanks.(1) Topography (topographic features,

waterways, swamps or marshes, vege-tation, location and size of possibledump or assembly areas).

(2) Exits (existing exits by roads ortrails; cross-country exits; roads, withdetails of width, surface, construction;railways, tramways).

(3) Aircraft landing sites within a 16- to24-kilometer (10- to 15-mile) dis-tance from beach (dimensions, sur-face, topography).

(4) Utilities (communications, electricity,water supply, transportation).

(5) Helicopter landing sites.

Section V. SURFACE MATERIALS

76. Types of Soilsa. Composition. Soil is defined as the uncon-

solidated material that overlies bedrock. Soilis made of disintegrated rock, in the form ofsand or clay, and humus, the disintegratedremains of past vegetation. Detailed informa-

tion about soils, their engineering properties,and testing techniques is contained in TM5-541. Some essentials of soils trafficabilityare given in chapter 9. For field identificationand classification, soils may be grouped intofive principal types: gravel, sand, silt, clay,

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and organic matter. These types seldom exist vary from lean clays (low plasticity) to fatseparately but are found in mixtures of variousproportions, each type contributing its charac-teristics to the mixture.

b. Gravel. Gravel consists of angular torounded, bulky mineral particles ranging insize from about 0.6 to 8 centimeters (1/4 inch to3 inches) in diameter. It is classified as coarseor fine; well or poorly graded; and angular,flat, or rounded. Next to solid bedrock, well-graded and compacted gravel is the most stablenatural foundation material. Gravel is easy todrain, easy to compact when well graded, af-fected little by moisture, and not subject tofrost action.

c. Sand. Sand consists of mineral grainsranging from about 6 millimeters (1/4 inch)down to about 0.08 millimeters (.003 inch) indiameter. It is classified according to size andgradation as coarse, medium, or fine; and asbeing angular or rounded. Well-graded angularsand is desirable for concrete aggregate andfor foundation material. It is easy to drain,little affected by moisture, and ordinarily notby frost action. Sand provides an excellent roadsubgrade material when it is confined. Care isrequired, however, to distinguish between a finesand and silt.

d. Silt. Silt consists of natural mineral grainsranging from about 0.08 millimeters (.603inch) to about .005 millimeters (.0002 inch)in diameter. It lacks plasticity and possesseslittle or no cohesion when dry. The termrock flour is commonly used to describe in-organic silts of glacial origin. All silts aretreacherous for trafficability and as a founda-tion material. Because of its inherent insta-bility, slight disturbances in the presence ofwater, such as traffic vibrations transmitted toa wet silt subgrade, will cause the silt to be-come soft or to change to a "quick" condition.When ground water or seepage is present,silts exposed to frost action are subject to in-tensive ice accumulation and consequent heav-ing. Silts are difficult to compact and drain.

e. Clay. Clay generally consists of particlessmaller than 0.005 millimeters (.0002 inch),microscopic in size. Its plasticity and adhesive-ness are outstanding characteristics. Dependingupon the proportion of coarser grains, clays

clays (high plasticity). Many clays which arebrittle or stiff in their undisturbed state be-come soft and plastic upon being worked.

77. Soil Mapsa. Contents. Soil maps or overlays indicate

the predominant soils in given areas, identify-ing them according to their engineering char-acteristics. Such maps may be constructed fromair photographs or ground reconnaissance ormade from existing soil and geologic maps andreports with the classifications expressed inengineering terms. Agricultural soil maps canbe large enough to provide detail for tacticalplanning, but often the designated soil typeapplies only to the surface soil. These mapsshould indicate the following properties ofsoils:

(1) Permeability.(2) Stability under stress.(3) Bearing capacity.(4) Important variations of (2) and (3)

above with changing moisture con-tent.

b. Coverage. For strategical planning, soilmaps should cover the area of the study. Alarge amount of general information may bepresented, because detailed plans may not befirm and the future weather conditions uncer-tain. The information includes the effects ofweather upon the soils. The reliability of theinformation must be clearly indicated.

e. Planning. Soil maps for tactical planningcover a smaller area than do strategical soilmaps. They are of a larger scale and containmore precise, detailed information. Greater ac-curacy is possible because more details areknown about the proposed operations. Recon-naissance and patrol reports make it possibleto check the ground, and weather forecasts areavailable to indicate what the prevailingweather will be. The information contained onsuch maps is useful in determining-

(1) Areas critical to cross-country move-ment as they affect both advances andcounterattacks.

(2) Stretches of road liable to failureunder heavy traffic.

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(3) Suitable and unsuitable areas for air- sand is an obstacle to vehicles, particularly onfields, field fortifications, and otherinstallations.

(4) Areas with soil conditions that areunsuitable for tank and vehicle parks.

(5) Difficult areas for field and air de-fense artillery deployment.

(6) River bank conditions for bridgefoundations and crossing operations.

d. Rear Areas. In planning rear area ac-tivities, soil maps are useful for determiningroad conditions. In order to stand up underheavy traffic during periods of frost and thaw,a road must have a well-drained subsoil foun-dation. A knowledge of the soils in an areawill reveal which stretches of road will be mostsusceptible to breakdown during a thaw, pro-viding a guide to selecting the best supplyroutes and indicating portions of the roadwhere precautions must be observed. Whensupplemented by an aerial reconnaissance, soilmaps are a valuable aid in highway locationand relocation. They indicate the soil areaswith desirable or undesirable engineering char-acteristics and also show the nearest sourcesof materials for road construction and mainte-nance. The information about soil conditionsgiven by a soil map is invaluable in selectingsites for airfields, storage installations, ammu-nition dumps, and vehicle parks. Preliminarystudy of the map prevents unnecessary fieldreconnaissance.

78. Military Aspects of Soilsa. Weather. The actual identity of the type

of soil in any area is of little practical valueunless the soil is also evaluated in relation tothe existing or predicted weather. In general,the major soil types have the following charac-teristics:

b. Gravel. Weather has little or no effect onthe trafficability of a gravel soil which is ex-cellent for tracked vehicles. It it is not mixedwith other soil, however, the loose particlesmay roll under pressure, hampering the move-ment of wheeled vehicles.

c. Sand. When wet enough to become com-pacted, or when mixed with clay, sand givesexcellent trafficability. Very dry, soft, or loose

slopes.

d. Silt. When dry, silt provides excellent traf-ficability, although it is very dusty. Silt ab-sorbs water quickly and turns to a deep, softmud when wet, imposing a definite obstacleto movement. It dries quickly after a rain, soonbecoming trafficable again.

e. Clay. When thoroughly dry, clay providesa hard surface with excellent trafficability, butit is seldom dry except in arid climates. Al-though clay absorbs water very slowly duringa rain, it also takes a long time to dry. Wetclay is very sticky and slippery. Slopes with aclay surface are difficult or impassable, anddeep ruts form rapidly on level ground. Acombination of silt and clay makes a particu-larly poor surface when wet.

f. Special Soil Conditions. If a soil has un-derlying bedrock near the surface, it will be-come thoroughly saturated after a rain. Thewater cannot drain away, making the surfaceuntrafficable.

g. Manmade Effects. Soil under cultivationbecause it has been worked is softer and ab-sorbs water more quickly than other soils andmay therefore have poorer trafficability. Usu-ally the presence of irrigation structures indi-cates that the soil is soft and contains waterand the soil generally will have poor traffica-bility. The types of crops cultivated in an areaprovide indications as to the nature of the soil.Since gravelly soils are especially suitable forfruit orchards, for example, the presence ofextensive orchards, especially on flat areas,may indicate that the soil has a high gravelcontent. Many cultivated plants have specificsoil and water requirements, giving a clue tothe soil and drainage of the area.

h. Nuclear Weapons. Soil composition anddensity affect the amount of damage by shockthat will result from a surface or subsurfaceburst. Propagation of the shock wave is poorestin light, loamy soils and best in plastic, wetclay. The pressures transmitted by the blastmay be 50 times greater than those trans-mitted through sandy clay. The size and shapesof craters produced by a surface or subsurfaceburst, their effectiveness as obstacles and the

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intensity and decay rate of induced radiation to transportation and power facilities. Plains,in the soil are also affected by the soil com-position and density.

79. Information Requirements-SoilsIn a terrain study, soil information usually

is presented in tabular form, with the datakeyed to a soil map or overlay. It covers--

a. Extent of each dominant soil type.

b. Depth of each type in areas indicated.

c. Surface texture (fine or coarse).

d. Parent material.

e. Description of material.

f. Properties when wet, dry, or frozen, in-cluding suitability for specified militaryvehicles under various conditions, bearingcapacity for structure foundations, and perme-ability when wet.

g. Variations from dominant soil type inspecified areas.

h. Areas of permafrost, permanent ice andsnow.

i. Seasonal state of the ground (dry, wet,flooded, frozen, snowcovered) by seasons,months, or shorter periods. Effects of eachstate on cross-country movement, construction,excavation, cover and concealment, and othermilitary aspects.

80. Rocka. Classification. Rock may be defined as the

firm and coherent or consolidated material ofthe earth's crust. Bedrock is solid undisturbedrock either exposed at the surface or underly-ing the soil. Igneous rock is formed by coolingand solidification from a molten or partlymolten state; sedimentary rock, from materialaccumulated as a deposit from water or the air,and metamorphic rock, by the recrystallizationof igneous or sedimentary rock under the in-fluence of heat, pressure, or both. The informa-tion, characteristics, and uses of rock are ex-plained in TM 5-545.

b. Underground Installations. Undergroundinstallations require rock and soil that areeasily worked and locations that are accessible

terraces, and alluvial fans usually are best forbunker type installations. The most favorableterrain for tunnels normally is found onplateaus, escarpments, high hills, and moun-tains with steep bare-rock surfaces. Largebunkers require deep, well-drained soils, withthe water table at least 4.5 to 6 meters (15to 20 feet) below the surface. They should beprotected against surface-water flooding, espe-cially if they are located on low plains. Militarytunnels may be constructed for tactical, com-munication, storage, and shelter purposes,including-

(1) Undermining of enemy positions andcountermining.

(2) Galleries for water supply.(3) Fortifications (headquarters, gun em-

placement, ammunition storage, de-fensive installations).

(4) Underground factories and hangars.

e. Tunneling.

(1) Construction. Before tunneling oper-ations are initiated, a geologist shouldevaluate the proposed site. Tunneltype installations are favored by high,steep slopes of exposed bedrock. Thetunnel is kept dry by placing thelowest levels above the water tableand by constructing it in rocks thathave a minimum of fissures, joints,and faults that would permit seepageand flooding. The size of the chambersdepends upon the stability of the rock.The thickness of natural cover re-quired to give adequate protectiondepends upon the type of rock andsoil, degree of soundness of the rock,absence of joints and fissures, and thesize and shape of the undergroundopenings.

(2) New methods. In Viet Nam extensivehand-dug tunnels and tunnel com-plexes have been found. They areusedeas hiding places, caches for foodand weapons, headquarters, and pro-tection against air attack and artil-lery fire. They have concealed en-trances and exits, camouflaged bunk-

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ers, trap doors, and dead ends toconfuse the attacker. One trap doormay lead to a short change-of-direc-tion tunnel and another door to asecond change of direction, and athird door to the main tunnel. Thereare also multilevel complexes withstorage and hiding rooms at lowerlevels. Some of these have air or waterlocks as "firewalls" to prevent blast,fragments, gas or smoke from passingfrom one section to another. The en-trances are camouflaged and booby-trapped.

81. Information Requirements-RockTerrain studies of an area will be concerned

chiefly with the availability of unexploitednatural deposits suitable for the constructionof roads, protective works, airfields, and under-ground shelters. The particular information

Section VI.

82. Broad Classification of PlantsVegetation may be classified in four broad

categories-trees, shrubs, grasses, and culti-vated vegetation. The type of vegetation in anarea gives an indication of the climatic condi-tions, soil type, drainage, and water supply.Seasonal seepage or a rise in the ground-watersupply often is indicated by vegetation suchas reeds, sedges, cottonwoods, and willows,which thrive wherever seepage occurs. Simi-larly, arid conditions are also indicated bycharacteristic desert vegetation. TM 5-545 de-scribes the indications typical of various plantspecies.

83. Trees

a. Definitions. Trees are defined as perennialwoody plants at least 10 feet in height, withsingle stems and definite crown shapes, Aforest is an extensive area covered by treesgrowing in a close formation, so close that inmost cases their crowns touch. Smaller areascovered by trees may be termed woods, groves,or woodlots. In the terminology used on U.S.Army maps, any perennial vegetation highenough to conceal troops or thick enough to be

that will be required depends upon the purposeof the study. Requirements may include-

a. Rock Deposits.(1) Location and extent of deposit.(2) Type and properties of the material.

(3) Suitability for construction use (asaggregate, binder, surfacing, ballast,riprap, masonry construction mate-rial).

(4) Accessibility.

b. Underground Shelters.

(1) Existing areas (mines, caves, under-ground manmade installations). Char-acteristics. Special constructions.

(2) Areas suitable for development (rockstructure, comparative advantagesand disadvantages of indicated loca-tions).

VEGETATION

a serious obstacle to free passage is classifiedas woods or brushwood. Commonly, a deepwoods is considered as one that is large enoughto provide ample concealed maneuver space forlarge units deployed in depth. This would in-clude a woods that would conceal both the as-sault and reserve echelons of a brigade in theattack. A shallow woods is one that is notlarge enough to conceal elements of this size.Dense woods are those where the growth isthick enough to interfere with visibility suf-ficiently to limit the maneuver of troops.

b. Characteristics. In temperate regions,trees are commonly found at elevations of notmore than 2,440 meters (8,000 feet) above sealevel. A good forest climate is one with a warm,rainy vegetative season, a continually moistsubsoil, and low wind velocity. The growth oftrees is greatly influenced by the temperatureof the air and soil; even the hardiest conifersrequire a mean warm month temperature of atleast 50° F.

c. Classification. Trees are classified as eitherdeciduous or evergreen (fig. 43). Deciduoustrees drop all their leaves seasonally, but ever-green trees retain their leaves throughout the

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year. Trees are also either needleleaf or broad- the year. Almost all deciduous forests are lo-leaf. In the middle latitudes, needleleaf treesare predominantly evergreen, and broadleaftrees are predominantly deciduous. In the hu-mid tropic, nearly all trees are evergreen' be-cause the climate remains uniform throughout

cated in the Northern Hemisphere. The impor-tant dimensions of trees in a wooded area arethe diameter of the tree stems at breast height,the average height of the trees, and the averageheight above ground of the lowest branches.

Figure 4A. Mixed vegetation, showing (a) evergreen trees, (b) deciduous trees,(c) brush, and (d) sedges (Northern Manitoba).

84. Low-Latitude ForestsIn the low latitudes, tropical rain forests,

swamp forests, and moss forests are the princi-pal types.

a. Tropical Rain. In the tropics, rain forests(selva) blanket many square miles of moistlow lands in regions where rainfall is heavyand well distributed throughout the year, withno marked dry season. The Amazon Basin andWest Central Africa are the two largest areasof tropical rain forest, although it is also foundalong many rainy coasts and on tropicalislands. This type of forest covers more thanone-tenth of the earth's total land surface andcomprises nearly one-half of the total forestareas of the world. The rain forest consists ofbroadleaf trees of many species that form acanopy thick enough to shut off most sunlight.The trees are commonly from 30 to 45 meters(100 to 150 feet) in heights, with large diame-ters, smooth trunks, and few lower branches.Lianas, rope-like plants that entwine them-selves around trunks and branches, are com-mon. Usually the undergrowth is not dense, al-though it restricts observation. In the deepestshade, there is usually only a thick mat of fernsor herbs that offers no obstacle to movement.

Typical jungle conditions, with thick and im-penetrable undergrowth, are characteristicchiefly of sections where light reaches the forestfloor, as one precipitous wet slopes, along riversand coasts, and in abandoned agriculturalclearings.

b. Tropical Swamp (fig. 44). This forestoccurs in low terrain near or in swampy re-gions. Mangrove swamp forests (fig. 45) coverlarge areas along tropical salt-water coasts,presenting an almost impenetrable barrier tomovement. This type of forest is found in thesoft mud around river mouths, deltas, and in-lets, along shallow bays on small islands, andupstream as far as the tidal influence is felt.Mangrove forests include several kinds of trees,all with thick buttressed roots that extend ashigh as 3 meters (10 feet) above the ground.These spread outward becoming interlaced ina network that makes movement by foot almostimpossible and prohibits any type of vehicularmovement. Nipa palms, which generally growin or near mangrove swamps, also presentalmost impassable barriers (fig. 46).

c. Moss. This forest is found in the higherlatitudes just above the rain forest areas,chiefly at altitudes of 915 meters (3,000 feet)

85


or higher on the tops of tropical mountains that conceals the earth. This moss often coverswherever high humidity and cloudiness arepersistent. The trees are small with long over-hanging branches. Moss grows on the branches,tree trunks, and ground, where it is intermin-gled with ferns and vines to form a blanket

chasms and ravines, making them appear tobe level terrain. The moss forest accordingly ishazardous to movement. It is dark and gloomyand so dense that very little sunlight penetratesthe canopy. Visibility is extremely limited.

Figure 44. Swamp forest (air view) (Sanibel National Wildlife Refuge, Florida).

Figure 45. Mangrove swamp (Malay Peninsula).

85. Middle-Latitude Forestsa. Types. The principal forest types in the

middle latitudes include Mediterranean scrubforests, broadleaf forests, and needleleafforests.

b. Mediterranean Scrub. These consist of

broadleaf evergreen trees adapted to regionswith long, hot periods of summer drought. Theyare found in the borderlands of the Mediter-ranean Sea, as well as in California, Chile,southern Australia, and the Capetown regionof Africa. These areas are subtropical, withmild, rainy winters and long, dry, hot sum-

86

i"-~~~~~41


Figure 46. Nipa palms (Northern New Guinea).

mers. This type of forest consists of low treesand woody shrubs. Where climate and soilconditions are most favorable, the virginforest is composed of low, widely spaced treeswith massive trunks and gnarled branches. Be-tween the trees the ground is completely orpartially covered by a pale, dusty bush andshrub vegetation resembling the soil in color.Cork oaks and olive trees are typical of thistype of forest.

c. Broadleaf. Most of the temperate broad-leaf forest is composed of deciduous trees witha seasonal leaf fall, such as oak, hickory, maple,ash, elm, walnut, beech, and poplar. Along thehumid subtropical margins of the middle lati-tudes, principally in southern Japan, NewZealand, and southeastern Australia, there areevergreen broadleaf forests that resemble rainforests, with dense undergrowth and heavyvines. Temperate broadleaf forests vary widelyin composition, the dominant tree species dif-fering from one region to another. In someareas there are many conifers among them andthe forest may be described as mixed.

d. Needleleaf. Needleleaf trees are almost ex-

clusively evergreen. The growth and discard ofthe needles is a continuous process not confinedto any particular period or season. Usually theneedleleaf forests occupy the colder continentallocations on the poleward side of the broadleafforests. In areas of poor sandy soils, or onsteep mountain slopes where soils are thin orrocky and temperatures are lower, needleleaftrees may supplant broadleaf trees even in themiddle latitudes. South of the great belts ofsubarctic needleleaf trees there are large areasof needleleaf trees that provide valuable timbersuch as the forests of the Pacific Coast, westernCanada, and Alaska. The southern pine forestsin the Atlantic and Gulf Coastal Plains of theUnited States also are major sources oftimber.

86. High-Latitude ForestsA wide belt of needleleaf forests extends

from coast to coast in the subartic regionsof Eurasia and North America below the tree-less tundra regions. This Eurasian forest isthe largest continuous forest area in the world.Needleleaf trees such as fir, spruce, larch, andpine predominate, although in the swamp areas

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there are some broad leaf trees such as aspen, of middle latitudes. In many arid and semiaridwillow, birch, or mountain ash. The area hasshort, cool summers and long, dry, cold wintersso that growth is slow, and few trees are morethan 0.45 meter (11/2 feet) in diameter. Thereare numerous large swamps and marshes cov-ered with moss, and containing such trees asbalsam and spruce. These areas usually rapidlybecome impassable after precipitation orduring a thaw.

87. Shrubsa. Description. Shrubs are woody plants

usually less than 3 meters (10 feet) high withmore than 1 stem. They include a variety oftrees that have had their growth stunted be-cause of soil or climatic conditions. Scrubgrowth includes cactus, stunted shrubs, sage-brush, mesquite, and similar plants found mostfrequently in arid or semiarid areas. Shrubscomprise the undergrowth in the open forests

areas they are the dominant vegetation. Theyare prevalent in the subarctic and in large,burned-over or cutover areas in humid regions.

b.. Classifications. Shrubs, like trees, areeither deciduous or evergreen, needleleaf orbroadleaf. In the middle latitudes, most broad-leaf shrubs are deciduous, and all needleleafshrubs are evergreen. In the humid tropics,nearly all shrubs are evergreen. Most arid re-gions of both low and middle latitudes havesome vegetation, both deciduous and evergreen,although it is sparse (fig. 47). It may consistof low bunch grass with widely spaced bushesor fleshy, water-storing plants such as thecacti. Most commonly, the vegetation comprisessagebrush and similar scrub growth. Peren-nial shrubs of the desert areas grow far apart,with considerable areas of bare soil in betweendue to the low rainfall. The rate of growth isvery slow.

Figure 47. Charaoteristic desert vegetation (Arizona).

88. Grasses

a. Kinds. Grasses include all kinds of non-woody plants. A grassland is an extensive areawhere the natural vegetation consists primarily

of grass. In low latitudes, grasslands often aretermed savannas; in middle latitudes, prairies(tall grass) and steppes (short grass). Grass-lands in wet or poorly drained areas commonlyare called meadows. For terrain intelligence

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purposes, grass more than (1 meter) 3 feet plants may be numerous. Steppe vegetation de-high is considered tall, and below that height,short.

b. Tropical Grasslands (Savanna). In areaswith heavy seasonal rains and a distinct dryseason, the grasslands or savanna are composedmostly of tall, very coarse grasses that growin tufts separated by intervals of bare soil. Ifthere are trees, they usually are species thatcan withstand seasonal drought and they growmostly in clumps in the grasslands or alongthe margins of streams. Savanna grass growsrapidly at the beginning of the rainy season,reaching heights of 1 to 3.5 meters (4 to 12feet) in a few months. When dry, the bladesbecome brown, stiff, and harsh in texture, burn-ing very readily. The grasses usually diminishin height with decrease in the annual rainfall,and trees become fewer until under semiaridconditions nearly treeless steppes, composed ofshorter grasses, are prevalent. Low-latitudesavannas are usually located between desertand forest regions.

c. Prairie. The prairie type of grass occursmost frequently in areas where the soil remainsmoist for a depth of 75 centimeters (30 inches)or more. The prairies are covered with tall,luxuriant, and relatively deep-rooted grassesthat grow to heights of from 30 to 90 centi-meters (1 to 3 feet). Over most prairie regions,rainfall varies between 50 to 100 centimeters(20 and 40 inches) annually. Usually there isa large variety of flowering plants in springand summer. The principal prairie regions in-clude parts of central United States and theprairie provinces of Canada; the ArgentinePampa, Uruguay, and southeastern Brazil; theplains of the Danube in Hungary and Rumania;and parts of Manchuria and southern Russia.

d. Steppe. A steppe is an area of short,shallow-rooted grasses typical of semiarid re-gions where the depth of moist soil is less than60 centimeters (2 feet). In common usage, theword steppe is used to describe all the drier,short-grass grasslands, both in tropical andmiddle latitudes. Some of the steppe grasseslie in a soft, fine mat on the ground, whileothers stand as hard, wiry tufts. Thorny shrubsand low, coarse bushes may dominate the steppein some sections. Cacti and other succulent

velops typically in regions that receive less than50 centimeters (20 inches) of rainfall a year,with a hot summer and a cold, dry winter.

89. Cultivated Vegetationa. Field Crops. Field crops constitute the pre-

dominant class of cultivated vegetation. Vinecrops and orchards are common but not wide-spread, and tree plantations are found only inrelatively few areas. The size of cultivatedareas ranges from paddy fields covering aquarter of an acre to vast wheat fields. In adensely populated area, where all arable landis cultivated, each parcel will be used for thecrop that brings the highest yield, making itpossible to predict the nature of the soils frominformation about the predominant crops.Rice, for example, requires fine-textured soils.Other crops generally must have firm, well-drained land.

b. Orchards. An area of orchards or planta-tions usually consists of rows of evenly spacedtrees, showing evidence of planned plantingthat can be distinguished on an aerial photo-graph. Usually such an area is free fromunderbrush and vines.

c. Rice Fields. Rice fields usually are floodedareas surrounded by dikes or walls approxi-mately 1/2 or 1 meter (1Y2 to 3Y2 feet) inheight and Y2 to 11/2 meters (11/2 to 41/2 feet)wide. When flooded for planting, the depth tothe bottom mud ranges from 15 to 90 centi-meters (6 inches to 3 feet).

90. Military Aspects

a. Key Terrain. Woods provide concealmentand cover for assembly areas and during theapproach march. Forests and heavy vegetation,however, increase the difficulty of maneuver inadvancing to attack and in launching the as-sault. The attacker may have little or noinformation about the roads, trails, and topog-raphy in the area not under his control, dueto the difficulty of securing detailed terrainintelligence without actual reconnaissance.Wooded and heavily vegetated areas providecover and concealment for organized positions,shelter for reserve formations, and an obstacleto the attacking forces. Usually the defender

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is able to make a detailed reconnaissance of influence of forests and heavy vegeta-the area, so that he is familiar with the roads,trails, and other features of the terrain. In-fantry weapons form the basis of the defense,due to the difficulty of securing observed ar-tillery fire in heavily wooded areas.

b. Observation and Fields of Fire.(1) Observation. The height and density

of the trees and other vegetationlargely determine the amount ofground observation that can be ob-tained. To secure an adequate field ofview from an observation post, it maybe necessary to clear away vegetationat the risk of losing concealment. Theeffects of cultivated crops upon ob-servation vary with seasonal condi-tions. In two or three weeks a corn-field may be covered with high stalksthat limit observation. Later in theseason, this corn may be harvested ina day, allowing observation again.

(2) Fields of fire. Lanes may be cutthrough vegetation to provide fieldsof fire, but it is seldom practical tocut lanes that extend far enough toprovide long-range observed fires. Ex-tensive clearing indicates the locationof weapon positions to the enemy. Theextent of clearing that is practicablewill depend upon the amount of vege-tation, its density, and the length oftime that the positions will be occu-pied. Indirect fire is less affected byvegetation than direct fire. Mortarsrequire little more than overheadclearance. Artillery weapons requiremore clearance than mortars, buthigh angle fire may be employed toavoid extensive cutting and clearing.Air defense artillery can be employedeffectively in forests and areas ofheavy vegetation when clearance re-quirements are met. Forests and heavyvegetation may be set on fire as atactical weapon, particularly duringdry season. Wooded areas and thosecovered with heavy vegetation tendto increase the persistence of gas andsmoke, particularly during wet sea-sons or periods of high humidity. The

tion upon nuclear weapons effectsvaries with the amount of overheadcover, density of growth, kind oftrees, nature of the tree crowns, un-dergrowth, and the litter on the forestfloor. Trees in leaf offer a high degreeof protection from thermal radiationif the cover is sufficiently continuous,but protection from initial nuclearradiation is insignificant.

c. Cover and Concealment. Thick forests ofdeciduous trees in leaf give excellent conceal-ment from air observation when troops observeproper precautions in camouflage and move-ment. Evergreen forests will provide conceal-ment throughout the year, changing color veryslightly from season to season. Deciduous treeslose their leaves, reducing concealment, andchange color, which increase the difficulty ofnatural camouflage. Usually undergrowth andsmall trees growing closely together give betterconcealment from ground observation than astand of larger trees. Unless the undergrowthis high, however, it will provide little conceal-ment from aerial observation. The amount ofconcealment and cover provided by cultivatedcrops depends largely upon seasonal conditions.Disruption of the agricultural pattern is readilyapparent to aerial observers and in aerialphotographs.

d. Obstacles. Fire lanes and certain types ofvegetation often canalize movement throughforest areas. This is true, for example whenlines of trees border streams. Normally, noserious obstacle to movement is offered byshrubs and grasses, but visibility can be re-duced in high grasses, with the added dangerof reptiles to foot soldiers. Small grain cropshold soil nearly as well as grasses, so thatmovement is better in such areas than in thoseplanted with row crops. Some parts of vine-yards present a tangled maze of poles and wiresthat constitute a definite obstacle to vehiclesand dismounted troops. The terraces and re-taining walls on hillsides are also obstacles.Wheeled vehicles and some tracked vehicles areunable to cross flooded paddy fields, althoughthey can negotiate them when the fields havebeen drained and the soil is thoroughly dry.In some cases even dried paddy fields remain

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a serious obstacle to movement because some Deeper taproots are developed where thevehicles are unable to negotiate the dikes sur-rounding the fields.

e. Avenues of Approach. In most woodedareas, individual trees large enough to stop atank are seldom so close together that theycannot be bypassed. Closely-spaced trees usu-ally are of relatively small diameters and canbe pushed over by a tank. The smaller treesand undergrowth, however, may be so densethat when they are pushed over the resultingmass of pileup vegetation will stop the tank.In most cases, wooded areas slow down themovement of tanks, and a guide may be re-quired to lead each vehicle. Cutover portions ofwooded areas usually contain stumps hiddenin tall grass or weeds that are serious obstaclesto armor. Trees that can stop a wheeled ve-hicle usually are too closely spaced to be by-passed. The pileup effect from pushing overvegetation is greater for wheeled vehicles thanfor tanks. Trailed loads are difficult to towthrough wooded areas. Woods slow down themovement of dismounted troops. Some types ofvegetation, such as mangroves or dense jungle,are frequently impenetrable until routes arecleared.

f. Construction.The usefulness of trees fortimber is determined by their height anddiameter, and by the nature of the wood ashard, soft, or fibrous. Deciduous trees generallyare hardwoods. Needleleaf trees are softwoodsthat usually are easily worked, although somespecies are fibrous and difficult to saw. When aforest area must be cleared of trees prior to aconstruction project, a study of the groundwill indicate the density and depth of the rootsystems. Where a forest is closely underlain byhardpan or rock, tree roots branch and remainnear the surface, making them easy to uproot.In soil that is firm, with deep underlying rock,trees tend to form large taproots extending toa considerable depth, making them diffi-cult to remove. Trees in inundated, marshy,and muskeg areas have thick widespreadingand shallow root systems near the surface ofthe ground. In northern regions where perma-frost occurs, its effect on the root systems oftrees is similar to that of hardpan or rock.Where the permafrost is near the surface, theroots branch and lie close to the surface.

permafrost is far below the surface.

91. Information Requirements-VegetationAs far as practicable, information about the

vegetation in an area is presented in the formof a map overlay that clearly indicates andidentifies the major vegetation types by theuse of color and symbols. The accompanyingtext briefly summarizes the additional infor-mation of military significance that cannot beshown adequately on the map. Pertinent infor-mation may include the following:

a. Forests.(1) Name or other identification.(2) Plant associations.(3) Principal species (names, proportion

in percent, density or average spac-ing, height range).

(4) Undergrowth species.(5) Canopy: structure (continuous, open,

broken) and seasonality (color, de-foliation).

(6) Duff (partly decayed vegetable mat-ter on the forest floor): abundanceand nature of fallen trees, logs, andso on.

(7) Exploitation practices (normal cut-ting, overcutting, undercutting).

(8) Operational aspects (suitability forcover, concealment, blowdown sus-ceptibility, camouflage, and fuel).

(9) Principal tree species.(a) Name (English and botanical).(b) Height (average).(c) Growth form (triangular, linear,

and ovate).(d) Diameter (average).(e) Leaves (broadleaf or needleleaf).(f) Period of defoliation.(g) Roots (structure, size, toughness).(h) Suitability for construction.(i) Special features (toxicity, thorni-

ness, edibility).(j) Indicator significance relation to

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regional and local climates, kindand state of ground, and groundwater, salinity, permafrost, depthand duration of snow cover, humanactivity).

b. Shrubs.

(1)(2)

Location and areal extent.Name or other identification.

(3) Principal species (names, proportionin percent, density or average spac-ing, height range).

(4) Foliage-density and seasonality(color, defoliation).

(5) Operational aspects (susceptibility tomass conflagration).

(6) Principal shrub species (for each).(Same information as for tree

species.)

c. Grasses.

(1) Location and area extent.(2) Identification.(3) Principal species (names, proportion

in percent, density, height range).

(4) Seasonality (dates of growth, color).(5) Operational aspects (susceptibility to

mass conflagration).(6) Principal species (for each).

(a) Name (English and botanical).(b) Date of maturity, height.(c) Life span.(d)Growth habit (sod or bunch).

(e) Suitability as forage.(f) Special factors (toxicity, irri-

tancy).(g) Indicator significance.

d. Cultivated Crops (general).(1) Location and areal extent.(2) Name or other identification.(3) Principal crops (names, proportion

in percent, density or spacing heightrange; if applicable, months planted,cultivated, and harvested; crop rota-tion practices).

(4) Canopy, foliage, or stand (as applica-ble: structure, color, defoliation, den-sity, rates of growth).

(5) Types of farming (irrigated, dry, andso on).

(6) Special factors associated with crops(irrigation ditches, flooding, terraces,hedgerows, dikes, and stone or othertypes of fences).

(7) Operational aspects (susceptibility tomass conflagration).

(8) Principal crops.(a) Tree and shrub crops (same infor-

mation as for tree species; in addi-tion, months that the crops areharvested).

(b) Grass and grain crops (same infor-mation as for tree species; in addi-tion, months of planting and har-vesting).

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CHAPTER 6

MANMADE TERRAIN FEATURES

Section I. SIGNIFICANCE

92. DefinitionManmade features include all the changes

in the natural environment made by man inthe course of living on the earth and using itsresources. Major manmade features are cities,defensive works, transportation and communi-cation facilities, and similar features that havesignificant effects upon the military opera-tions. Others are such features as cemeteries,hedgerows, and buildings, which affect onlylocal operations.

93. Military AspectsIn preparing terrain studies, manmade fea-

tures must be evaluated to determine theireffect upon the military aspects of proposedoperations. Recommendations may be made todestroy certain features or to retain them forfuture use after the operation has been com-pleted. Usually each major manmade featureis the subject of a detailed study by militaryintelligence personnel.

Section II. LINES OF COMMUNICATION

94. ImportanceThe lines of communication of an area con-

sist of all the roads, railways, and waterwaysover which troops or supplies can be moved.The importance of particular features will de-pend upon the unit and the type of operations.The ability of an army to carry out its missiondepends greatly upon its lines of communica-tion. One of the primary considerations inplanning large-scale operations is the extentand general nature of the transportation net-work. Planners must consider the advantagesand disadvantages of the entire pattern oftransportation facilities. An area with a densetransportation network, for example, is favor-able for major offensives. One that is criss-crossed with canals and railroads, but pos-sesses few roads, will limit the use of wheeledvehicles and the maneuver of armor andmotorized infantry. Railroads extending alongthe axis of advance will assume greater impor-tance than those perpendicular to the axis, andthe direction of major highways and water-ways assumes equal significance.

95. Roads and Routesa. Description. The term roads includes all

types of roads and tracks, but pack trails andfoot paths are not included. Bridges, ferries,snowsheds, and similar structures and facil-ities that provide continuity of movement andprotection for the way are also considered asintegral parts of the road system. An adequateroad system is a fundamental requirement inthe conduct of any major military operation.Terrain studies must provide informationabout the roads which exist in the area underconsideration and should indicate any majorrepair or rehabilitation required on existingroads, or where now roads will be needed tosupport a proposed operation. Roads in thecombat zone usually need meet only minimumstandards, but those in rear areas, especiallyin the vicinity of water terminals, airfields,supply installations, and those used as MSR'smust be well-surfaced and capable of carryingheavy vehicle traffic without excessive main-tenance. Operations on a wide front and theemployment of nuclear weapons will require

93


a large number of secondary roads in both able in adverse weather and cannotforward and rear areas. The information pre-sented in a terrain study should indicate theminimum maintenance and construction re-quirements that may be anticipated during aplanned operation. Continual maintenance ofroad net is essential. In addition to the severepunishment given to roads by large volumes ofheavy traffic, important bridges, intersections,and narrow defiles are primary targets forenemy bombardment. The maintenance of un-necessary roads must be avoided, and the con-struction of new roads held to a minimum.

b. Route Types. Routes usually are classifiedas follows:

(1) All-weather route (Type X). Anyroute which with reasonable main-tenance is passable throughout theyear to a volume of traffic never ap-preciably less than its maximum ca-pacity. The roads which make up thistype of route have a waterproof sur-face, adequate drainage, and are onlyslightly affected by precipitation ortemperature fluctuations. At no timeis it closed to traffic by weather ef-fects other than snow blockage. In thisroute class are roads paved withconcrete, bituminous surfacing, brick,or paving stone.

(2) All-weather route (Type Y) (Limitedtraffic due to weather). Any routewhich with reasonable maintenancecan be kept open in all weather, butsometimes only to traffic considerablyless than maximum capacity. Theroads which form this type of routedo not usually have waterproof sur-faces and are considerably affectedby precipitation or temperature fluc-tuations. Traffic may be halted com-pletely for short periods. Heavy useduring adverse weather conditionsmay cause complete collapse of thesurface. Crushed rock or waterboundmacadam, gravel, stabilized soil, orsand-clay, are typical roads in thisroute class.

(3) Fair-weather route (Type Z). Aroute which quickly becomes impass-

be kept open by maintenance shortof major construction. This type ofroute is so seriously affected byweather that traffic may be broughtto a halt for long periods. In this routeclass are roads of natural or stabil-ized soil, sand-clay, shell, cinders,laterite, and other lightly metalled orlight aggregate surfaces.

c. Location and Use. Military routes areclassified also as follows:

(1) Axial route. Axial route is part ofmilitary road net work, and it leadstoward the front and is generallyperpendicular thereto. When desig-nated as the principal traffic arteryof a division or higher unit, such aroute is termed a main supply route(MSR). When designated the prin-cipal traffic artery of a brigade orbattalion, such a road is termed asupply route (SR).

(2) Lateral route. A route which gener-ally parallels the front and leads intoand across axial routes.

(3) Reserved route. A controlled routeallocated exclusively to a command orunit, or intended to meet a particularrequirement.

(4) Supervised route. A route over whichcontrol is exercised by means of traf-fic control posts, traffic patrols, orboth.

(5) Dispatch route. A route over whichfull control, both priority and regula-tion of traffic, is exercised.

d. Adverse Terrain. Swamps, bogs, and low-lands such as delta areas may create specialproblems of drainage and ditching, necessitateadded support to the roadbed and require theconstruction of many bridges. Rugged topog-raphy may result in steep grades and sharpcurves, tunneling, bridging, cuts, and sidehilllocations in laying out new roads. Sidefiill lo-cations, in turn, may require retaining walls,cribbing, and snowsheds to give protectionagainst earth, rock, or snow slides. In the des-ert, sand fences and special crews and equip-

94


ment to keep the roads clear of drifting sands map overlays that show the alinement of themay be required. Arctic terrain requires spe-cial techniques to build and maintain roads onpermafrost and periodically frozen ground.

e. Weather and Climate. Sustained periodsof freezing, heavy snowfalls, and similar ex-treme weather conditions may seriously affectthe use, maintenance, and construction ofroads. Protection must be provided againstsnow drifts, and provisions made to removethe snow and to repair damage due to frostheave and frost boils. Excessive rainfall mayresult in washouts and flooding in low areasand cause earth and rock slides in rugged ter-rain. Continuous wet weather may make un-surfaced roads impassable. In dry periods, dustcontrol becomes an important factor on un-surfaced roads.

f. Design and Construction. Terrain studiesshould include an engineering evaluation of thestructural soundness of all roads in an areaunder consideration. If the initial design didnot provide for the increased loads and speedsthat would accompany military use or if theroad was improperly constructed originally, itmay prove a serious obstacle to movement. Re-pairs and excessive maintenance may be re-quired because of an unstable subgrade; inade-quate drainage of the subgrade, surface, orslopes; sharp curves, and loose or unsealedwearing surfaces that result in saturated road-beds.

g. Poor Maintenance. Poor maintenance of aroad is shown by clogged culverts and ditches,potholed, bumpy, and rutted surfaces, soft anduneven shoulders, and badly worn and crackedpavements. Studies should indicate wherethese conditions exist and the maintenancethat would be required to bring the roads upto minimum military standards.

h. Trafficability. The various types of soilsaffect trafficability differently. For examplesandstone affords excellent trafficability whenit is dry but is reduced to good trafficabilitywhen,wet; trafficability on a clay surface israted as fair when dry and impassable whenwet. "

96. Information Requirements - Roadsa. Information about roads is recorded on

significant roads, with the location of associ-ated bridges, tunnels, ferries, fords, and criti-cal points such as rockslide areas. Ordinarilythe local system of route numbers is used, butif no system exists that is satisfactory forterrain intelligence purposes, an arbitrarysystem is used to identify the main and sec-ondary roads.

b. Information about individual roads usu-ally includes the following:

Name and route number.Terminal points; intermediate local-ities on the road; distances betweenmajor points.

(1)(2)

(3) Terrain (elevations, irregularities,slopes, drainage, soils).

(4) Length and width.

(5) General condition (necessary repairsand improvements, with nature andlocation).

(6) Surface material (by sections, ifthere are changes in type of surfacealong the route).

(7) Ratings of alinement, drainage, foun-dation, and surface.

(8) Roadbed (width of traveled way; typeand width of shoulders).

(9)(10)

(11)

(12)

Maximum grade.Sharpest curvature.Significant cuts and fills.

Clearance (minimum vertical andhorizontal clearances, with nature ofrestrictions).

(13) Bridges (load capacity, general con-dition).

(14) Tunnels (length, widths, clearances,condition).

(15) Fords and ferries (type, generalcharacteristics, condition).

(16) Critical points; location and charac-teristics of possible bypass routes ordetours around bottlenecks.

(17) Location and characteristics of routesthat provide maximum protectionfrom ground or air attacks.

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(18) Snow (critical areas, snow fencing, cover while awaiting their turn tosnow removal equipment). cross.

97. Bridgesa. Importance. Road and railway bridges are

vulnerable points on a line of communication.Timely preservation, destruction, or repair ofa bridge may be the key to an effective de-fense or to successful penetration of an enemyarea. A bridge seized intact has great value inoffensive operations, since even a small bridgefacilitates the movement of combat troopsacross a river or stream. Information aboutbridge types and their classification is con-tained in TM 5-312 and FM 5-36.

b. Sites. Because of the time and labor in-volved, new bridges are erected only when anexisting bridge, ford, or detour cannot be used.Terrain suitable for a bridge site should meetthe following requirements:

(1) Satisfactory river conditions, with nofast currents or great depths.

(2) Site readily accessible from the roadit serves.

(3) Firm, well-drained approaches, pref-erably above flood level.

(4) For floating bridges, a riverbed freefrom snags, rocks, and shoals to aminimum depth of three feet andfirm enough to hold anchors and tosupport trestles. Banks should befrom two to six feet above water levelto minimize excessive abutment prep-aration.

(5) Firm, stable banks of suitable height.Large differences in bank height re-quire excessive grading. Low banksmay be subject to a rising river levelthat will flood the bridge site.

(6) Adequate, well-drained workingareas close to the site including abivouac for the working party, spacefor construction materials, and turn-arounds and parking places for ve-hicles and heavy mobile equipment.

(7) Areas close to the site, near or along-side the approach roads, where ve-hicles can park off the road and under

98. Information Requirements - Bridgesa. Detailed information about bridges can-

not be obtained from topographic maps, butindications on air photographs usually willpermit an approximate determination of thewidth, clearance, and height above water of abridge. Details such as the condition, capacity,and structure of a bridge should be obtainedby engineer reconnaissance. Reconnaissanceprocedures are described in TM 5-312 and FM5-36. Basic information requirements for abridge should include a summary of its struc-tural characteristics, its critical dimensions(length, usable width, overhead clearance), anestimate of capacity, and general condition.

b. Detailed information includes the follow-ing:

(1) Type, number of lanes and width ofeach, number of spans and length ofeach length of panels, arrangementof spans.

(2) Height above riverbed, overheadclearance for vehicles, class.

(3) Stream data: width, depth, velocityof current, direction of flow, type ofbottom, estimated bearing capacity ofbottom, height, slope, and nature ofbanks.

(4) Description, dimensions, and condi-tion of access roads and approaches.

(5) Type, dimension, and condition ofabutments, stringers, flooring, gird-ers, and other structural elements.

(6) If damaged or wrecked-(a) Structural details of bridge in its

original form.(b) Nature and extent of damage; po-

sition of debris; details regardingany salvageable materials.

(c) What loads, if any, can still crossthe bridge.

(d) If not suitable for use, informationabout alternate sites.

99.a.

RailwaysProperty. The term railway includes all

96


fixed property belonging to a line, such as f. Military Use. Railways are desirable forland, permanent way, bridges, tunnels, andother structures. Railways assume increasedmilitary importance in areas where the soilsare generally untrafficable, roads are poor, andrail transportation facilities are extensive.Frequently, railways can be used as substituteroads fo) vehicles. Most railway bridges willcarry"ta4hks without reinforcement. The basicelements of a railroad include motive power,rolling stock; trackage; yards, terminals, regu-lating stations, and railheads; transshipmentpoints; water and fuel stations; maintenanceand repair facilities; and signal communica-tion facilities.

b. Yard. A yard is an area containing a sys-tem of interconnected tracks and is used formaking up trains, storing cars, and generalmaintenance activities.

c. Railhead. A railhead is the point at whichsupplies destined for a particular unit, instal-lation, or area are transferred from rail to an-other type of transportation, usually trucks.

d. Regulation. A regulating station is aninstallation on a military railway line at whichthe movement of supplies and personnel iscontrolled. Its facilities include a yard, open andcovered storage, and usually, temporary hous-ing and messing facilities for transient per-sonnel.

e. Construction. The development and extentof a railway system largely reflect the topog-raphy of the region that it traverses. In desertregions, for example, a single railroad may ex-tend in a straight line across vast barrenwastes. In hill regions and mountain areas, therailways run through valleys, with short linesleading off into other terrain. On plains, rail-ways will have few curves but may be subjectto the effects of poor drainage conditions. Gen-erally, railways tend to follow rivers becauseof the more uniform grades, the availability ofstraight routes, and the concentration of re-sources, industries, and population centersalong the waterway. The terrain characteris-tics of an area can be determined to a consid-erable degree by a study of the railway routes,since the rail lines almost invariably followthe topography that offers the fewest obstacles.

extended military operations. Their capabili-ties are of primary concern and are the sub-ject of continuing studies by personnel at thehighest levels. Detailed intelligence about therailways in an area of operations is producedby specialists of transportation and engineerunits. Railways are highly vulnerable to enemyattack, particularly to sabotage and guerrillaoperations. Keeping a railroad line in operationrequires trained security forces and extensiveprotective measures.

100. Evaluation of Railways

In evaluating a railway for terrain intelli-gence purposes, consideration should be givento the effects of adverse terrain, weather andclimate, and the overall design and construc-tion of the system. The following factors shouldbe considered:

a. Adverse Terrain. Railways passing overswamps, bogs, and delta terrain may encounterspecial problems of drainage, ditching, androadbed maintenance. In mountainous areas,steep grades, sharp curves, and tunnels arecommon. Because of sidehill locations and deepcuts, there should be protection against earth,rock, and snow slides. In desert, drifting sandis a problem and provisions should be made toremove it.

b. Adverse Weather and Climate. Severewinter conditions seriously retard operationand maintenance of railways, requiring pro-tection against drifting snow, provisions forsnow removal, and repairs because of damagecaused by frost heave. Excessive rainfall mayresult in washouts and flooding in low areasand cause earth and rock slides in rugged ter-rain.

c. Design. A railway may prove inadequatebecause the initial design did not provide forthe increased loads and speeds or heaviervolume of traffic needed. As a result, a railwaymight require either considerable reconstruc-tion and repair or extensive maintenance.Among the more common defects are an un-stable subgrade, lack of adequate drainage,light rail, poor ballast, and untreated ties. Im-proper maintenance is evidenced by such con-

97


ditions as an uneven roadbed, improperlytamped ties, loose fastenings, badly worn rail,or uncleared drains.

101. Information Requirements - RailwaysRailway information should be recorded on

a map or overlay that shows the true alinementof all rail lines; their trackage, gage, andstatus; and the location of selected bridges,tunnels, and ferries. A convenient system ofline numbers is used based on a standard ref-erence or arbitrarily selected. Fundamental in-formation about railways should include thefollowing:

a. Total mileage.

b. Terminals and details of main lines.

c. Mileage by gage and locations of changes.

d. Number of tracks.

e. Maximum grade and minimum radius ofcurvature.

f. Location and length of passing tracks.

g. Type and weight of rail.

h. Permissible loads; capacity of bridges.

i. Yards and terminals (location, type, ca-pacity).

j. Details of servicing facilities and otherinstallations.

k. Operating factors (cars per train; speed;number of daily trains each way).

1. Bridges and tunnels (bridge data to in-clude length, number of tracks, spans by typeand length, height of structure; tunnel data toinclude length, number of tracks, and lining).

m. Rail ferries (location, type, capacity).

n. Electrification (location, type).

o. Transshipment points.

p. Individual rail line details-(1) Name.(2) Terminals, intermediate stations,

length of each stretch.(3) Obstructions (demolitions, washouts,

blocked tunnels).

(4) Gage.(5) Number of tracks.(6) Weight of rails.(7) Maximum grade and minimum ra-

dius of curvature with location ofeach.

(8) Ties, ballast.(9) Sidings and passing tracks (location,

lengths, switches).(10) Tunnels (locations, clearances).(11) Overhead structures and vertical

clearances.

(12) Drainage facilities, including cul-verts.

(13) Bridge data.

(14) Operating and servicing facilities (lo-cation, availability of fuel and waterand ice; signal, traffic control, anddispatching facilities).

(15) Availability of trained and depend-able personnel.

(16) Transshipment points.

q. Equipment.(1) Present condition, and interchange-

ability with equipment of other coun-tries.

(2) Motive power (type, size, weight,tractive effort, wheel arrangement,type and height of couplings).

(3) Rolling stock (type, number, car di-mensions, capacity, weight).

(4) Rail cars self-propelled and trailer-type, total by type, size, capacity.

(5) Work cranes (total by type, size,capacity).

(6)(7)

Snow plows (total by type, size).Armored equipment (total by type,size).

(8) Repair shops (location, types ofequipment repaired, capacity by type,number of personnel employed).

102. Inland Waterways

a. Definition. The term inland waterway is

98


applied to those rivers, canals, lakes, and in- Streams of low and uniform gradients usuallyland seas of a country which are used as ave-nues of transport. It includes all the fixedstructures which affect the movement of ves-sels carrying passengers or freight. Types ofinland waterways include inland lakes andland-locked seas, rivers, and ship and bargecanals, and the intracoastal waterways, usu-ally running parallel to the coastline of a landmass and sheltered enough to permit the navi-gation of small vessels.

b. Classification. Inland waterways can beclassified according to their depths as follows:

(1) Very shallow. Depths less than 1.4meters (41/2 feet).

(2) Medium. Depths between 1.4 and 2meters (41/2 and 6V2 feet).

(3) Deep. Depths greater than 2 meters(6V2 feet).

c. Advantages. Inland waterways provide aneconomical form of transportation for bulksupplies, freeing faster modes for shipmentsof a higher priority. Frequently, large or veryheavy items that cannot be handled by truckand rail can be shipped by waterway. One ofthe major uses of waterways in an activetheater is the transportation of supplies forthe rehabilitation of the economy in liberatedareas, thus reducing the demands upon mili-tary transportation facilities.

d. Limitations. Unless icebreaking operationscan be conducted, traffic is halted completelyduring a freezing period. The thaw followinga freezeup may cause floods, and periods ofdrought may result in insufficient water forthe movement of vessels. The locks, bridges,cuts, dams, and other facilities are vulnerableto enemy action. Retreating enemy troops usu-ally drop rail or road bridges into the water-way; damage locks and levees; obstruct chan-nels with ships and barges; drain canals; anddestroy, dismantle, or move essential equip-ment. Waterway transport is slow. It is alsoinflexible, since new waterways cannot beconstructed during military operations. Thedepths of rivers and streams used as water-ways fluctuate with maximum and minimumrainfall. Streams with fairly direct coursescommonly are interrupted by falls and rapids.

meander. Their channels shift constantly, de-positing sandbars, which are a menace tonavigation.

103. Information Requirements -Waterways

Inland waterway information should be re-corded on a map or overlay that shows the truealinement of the navigable waterways, the lo-cation of all locks, dams, aqueduct bridges, tun-nels, and major landing facilities, and thelocation of specific structures which limit thevertical and horizontal clearances on eachnavigable reach. The local names are used toidentify waterways and structures wheneverfeasible. Detailed information requirementsshould include the following:

a. Developed Waterways.(1) Geographical location (name, origin,

terminus, length).(2) Restricting widths and depths of

channel.

(3) Frequency, duration, and effects ofseasonal changes (floods, low water,droughts, excessive currents, normalfreezeup and opening dates).

(4) Location, description, and restrictiveeffects of structures (locks, safetygates, dams, bridges, ferry crossings,aqueducts, tunnels, cable crossings).

(5) Speed and fluctuation of current.

(6) Name and location of waterwayports, including length of alongsidewharfage and depths, and data onmechanical handling, storage, clear-ance and ship repair facilities.

(7) Maintenance requirements.

(8) Craft (number, type, cargo capaci-ties).

(9) Communication facilities.(10) Availability of labor force.

b. Navigable Rivers. In addition to theitems listed in a above, the following addi-tional information may be required:

(1) Physical characteristics of the river

99


(bottom, banks, feedwater streams,and important tributaries).

(2) Navigational hazards, such as falls,rapids, and sandbars.

(3) Navigational aids, location, and type

(buoys, lights, range markers, radar,foghorns).

(4) Changes in channel.

(5) Dredging requirements.

Section III. PETROLEUM AND NATURAL GAS

104. Locationa. Source. Oil is found only in the stratified

sedimentary rocks and sands of ancient sedi-mentary basin areas. Because of geologic up-heavals in past ages, today's oilfields may befound along the foot of mountain chains or inlowland or offshore areas. Petroleum, gas, andwater are commonly found together.

b. Gas. Natural gas is found alone, as wellas with petroleum. Gas from oil wells is com-monly entrained with natural gasoline and isknown as wet gas. When economically feasible,wet gas is piped to an absorption plant, wherethe gasoline is extracted. Gas from gas wellsordinarily is relatively free of natural gasolineand is known as dry gas. If sufficiently free ofother unwanted gases and impurities, dry gasmay be fed directly into pipelines for distri-bution.

105. Installations

a. Derricks are commonly the most distin-guishing features of an oil or gas field. A der-rick is required to position and handle thelong sections of drill pipe and other equipmentused in the well when drilling for oil. Depend-ing on the type, the cost of moving or futureneeds, a derrick may or may not be left inplace indefinitely following the completion ofthe well. Where a continuing need exists, thedrilling derricks may be replaced with smallerderricks or gin poles. A producing oil well ischaracterized by a pump or by a "Christmastree," so called because of its tree-like appear-ance. A pump is used where the subterraneangas pressure is too low to force oil to the sur-face. A Christmas tree is used where the under-ground gas pressure is sufficient to force oil tothe surface. It consists of a system of pipes,valves, and gages capping a well for controllingthe flow of crude oil and gas.

b. Refineries are located near either produc-ing oil fields or distribution centers in majorconsuming areas. Adequate all-weather trans-portation and an abundance of cooling waterare essential. Tall, cylindrical distillation or"cracking" towers are the most prominentfeatures at refineries. Other equipment includeslarge furnaces, cooling towers, electric powerplants or substations, and intricate pipingsystems. Tankage for storing crude oil chargestocks and semirefined and refined products isalso required. Refinery capacities are usuallyrated in barrels per day (42 U.S. gallons perbarrel) or metric tons per year of crude oilrun to stills (crude oil started through therefining processes). A reliable rule of thumbfor converting barrels per day to metric tonsper year is to multiply the number of bar-rels per day by 50. Metric tons per year aredivided by 50 to yield barrel-per-day figures.Crude oil for refinery fuel or lost otherwiseamounts to about 7 to 10 percent of refinerycapacity.

106. Distribution

a. Systems. A bulk distribution system forpetroleum products may include ship-to-shoreand dockside loading and unloading facilities,bulk storage tank farms, pipelines, pumpingstations; bulk delivery points or pipeheads,warehouses, open storage areas, canning anddrumming facilities and testing laboratories.Ocean-going tankers, tank barges, railroadtank cars, and tank trucks are also includedin integrated distribution systems. For terrainintelligence purposes, pipelines and storagefacilities are the most significant features ofa distribution system.

b. Pipelines. Pipelines commonly consist ofpiping, pumping equipment, and regulatingtankage. Other supporting equipment may in-clude tele-communications facilities, cleaning

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devices and trays for removal of unwanted the product stored. The tanks may be corn-condensates or contaminants, control and heat-ing devices. The capacity of a pipeline is ex-pressed as a quantity of liquid capable of beingtransported per unit of time, ordinarily in thenumber of barrels, metric tons, or cubic metersper day. The quantity of fuel actually trans-ported, usually will not exceed about 85 percentof the pipeline capacity.

c. Military Pipelines. Military pipelines areused chiefly to transport jet fuel and gasoline.Occasionally they are used also to transportdiesel fuel and kerosene. Commonly, 15-cm(6-inch) pipe is used; 20-cm (8-inch) pipe isemployed for ship unloading or trunk lines.The pipeline follows the most direct level route,within six to nine meters (20-30 feet) of all-weather roads, so as to facilitate construction,partrol, repair, and security of the line. Cross-country cutoffs are used where roads windexcessively. A military pipeline is divertedaround difficult terrain, such as marshes,swamps, or land that is subject to periodicflooding. It also avoids populated areas andmilitary installations that have a high elementof hazard, such as ammunition dumps. Baseterminals are located in rear areas, at or neartheater ports of embarkation or other tankerunloading points, but pipehead terminals arelocated at the forward end of a military pipe-line, moving forward with the army supplypoint to support the advancing forces.

d. Civilian Pipelines. Civilian pipelines areimportant for potential military support. Theyare generally permanently installed cross-coun-try along the most economical route. These pipe-lines may range from about 10 cm (4 inches)to more than 100 cm (40 inches) in diameter.Pipe of extremely large diameter is ordinarilyused only for natural gas or crude oil. Pipe-lines for crude oil are much more commonthan those for refined products, although useof the latter is rapidly growing. Crude oil pipe-lines can be converted for handling refinedproducts. This is a costly and time-consumingundertaking, particularly if aviation-gradefuels are to be transported.

e. Tanks. Bulk petroleum and refined pro-ducts are stored in tanks which differ greatlyin size, shape, and construction, according tothe function of the tanks and the nature of

pletely above ground, partly or entirely buried.Tanks above ground are surrounded by dikesor low walls to form catch basins and to pre-vent the occurrence or spread of fires if thetanks are ruptured or overflow. Tanks areburied or partly buried for reason of safety, toreduce evaporation losses, for concealment, orto reduce their vulnerability to military attack.A group of storage tanks is called a tank farm.Tank farms vary greatly in size; some comprisemajor storage complexes, with storage capaci-ties of millions of barrels. Ordinarily, the tanksare interconnected by an assembly of pipes andvalves called a manifold, which permits themovement of products. Because of their vulner-ability to air attack, and to nuclear attack,military tanks farms are limited to a totalcapacity of no more than 250,000 barrels.Military storage tanks are made of steel oraluminum and have capacities up to 10,000barrels. Portable fabric tanks also are usedin military operations at forward supply pointsand at beachheads.

107. Military Importance

a. Targets. The petroleum and natural gasresources of a country or region are valuableassets to its economy, and the degree of self-sufficiency in military fuels is fundamental toits conventional military capabilities. Accord-ingly, refineries, terminal facilities, distribu-tion systems, and storage installations areprimary targets for air attack and are majorobjectives. Major oil producing areas and re-fineries, key pipelines, storage facilities, andmarine terminals may be the principal ob-jectives of a campaign to seize them for our useor deny them to the enemy. The most militarilysignificant natural gas facilities are pipelines,which could be readily converted for handlingpetroleum products for military support.

b. Planning. Because military planners areinterested in the availability of fuel for mili-tary use, avoiding possible disturbance tolocal economics, the typical normal operatingconditions with respect to petroleum facilitiesare important. Included are seasonal variationsin the supply and demand for petroleum pro-ducts, and the principal consumers and theirneeds. Manufacturing and civil transport

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fuel requirements, as well as agricultural con-sumption by tractors and irrigating systemsare militarily significant in modern planning.

108. Information Requirements - Petroleumand Natural Gas

The location and extent of petroleum andgas facilities should be recorded on a topo-graphic map of suitable scale. A numberingsystem is established to identify the petroleumand the gas pipelines, producing fields, plants,and storage facilities. A separate series ofnumbers is used for each pipeline. Such pipe-line facilities as pumping stations and tankfarms are numbered serially, beginning froma designated initial point on the line. Localnames may be used for individual installations.Basic information should include the following:

a. General.

(1) Location and type of raw material(oil, oil shale, natural gas) ; characterof crude oil; well logs; and a geologiccolumn which designates the produc-ing formations and the depth to pro-ducing horizons.

(2) Reserves of raw material in millionbarrels, metric tons, or million cubicfeet (cubic meters).

(3) Administrative, maintenance, and re-pair facilities.

(4) Security and safety provisions.(5) Physical condition of installations

and equipment; required major re-pairs or improvements.

(6) Availability of trained and reliablepersonnel.

(7) Principal consumers.

b. Refineries.

(1) Location and owner/operator.(2) Capacity.(3) Details of construction; type of equip-

ment.(4) Nature and quality of products pro-

duced.

c. Pipelines.

(1) Name, if any; location of lines;material transported.

(2) Terminals.(3) Number and diameter of pipes;

delivery capacity of system at presentand under normal conditions; contentof pipeline when full.

(4) Facilities at base terminal (if a waterterminal, method of loading fromtankers).

(5) Storage facilities at terminals andalong pipelines; capacity of each in-stallation.

(6) Pumping stations (location, capacity,equipment).

d. Storage.

(1) Location: geographic coordinates; to-pography; adjacent landmarks.

(2) Surface tanks: types and number;dimensions; protection (revetments,blast walls).

(3) Buried tanks; number; dimensions.

(4) Pump houses: location; number;dimensions; capacity.

(5) Connecting pipelines and distributingsystems.

(6) Stocks (location and type).

Section IV. MINES, QUARRIES, AND PITS

109. Mines

a. Mineral Resources. The important mineralresources of a country include metallic oressuch as iron, copper, zinc, lead, tin, silver, gold,and uranium; mineral deposits, principallysulfur, phosphate rock, gypsum, graphite, as-bestos, and bauxite; and solid fuels, chiefly

coal, lignite, and peat. Terrain studies list eachsignificant mineral, covering in detail theestimated quantities available and the methodsand facilities employed to mine, process, anddistribute each type of mineral. Mineral de-posits are exploited either from the surface ofthe ground or from underground shafts andtunnels, the method depending upon the depth

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of the deposit below the surface. A typical mineral being removed by power shovels.underground mine consists of a vertical shaft,horizontal passages opening out of the shaft,and passages driven from above (winzes) con-necting the levels. Openings branching off fromthe levels, where the ore is actually extracted,are called stopes. Supports in mine workingusually are made of timber treated with pre-servatives or of reinforced concrete, steel, brick,or stone. Pillars of ore may be left as supports,finally being mined when the workings arevacated. Where ore beds lie close to the surface,the mineral may be removed from open pitsafter stripping off the overlying earth androck. This is strip mining, the coal or other

b. Placer. Placer mining involves the removalof the unconsolidated rock material that liesabove bedrock by hand, hydraulic nozzles ordredges, and subsequent separation of theore from waste by panning and sluicing. It iswidely employed to mine gold.

c. Open-pit. In open-pit mining, an excava-tion is made. In the case of deep pits, the sidesusually are cut into steps or benches. Accessto the below-ground-level site may be obtainedby arranging these benches in spiral form, bycutting inclined approaches, or by sinking ashaft connected to the mine by an adit or tun-nel (fig. 48).

~~~~~- - -"----

- --.--- -.- 2

II-;1~ Ili -'l

"Y-~~~~P~~~r~~-- .

Figure 48. Open-pit copper mine.

d. Glory-Hole. In glory-hole mining, the ex-cavation is funnel-shaped, and a vertical pas-sage (raise) driven from below connects withan underground haulage level. The ore slidesdown this passage into the haulage level forremoval.

e. Military Considerations. The ability of anynation to support a war depends upon its miner-al resources and enemy mines are accordingly

a major objective for air attack. The seizure ordefense of important mines may also be themission of troop units of any size. Minesprovide concealment and cover, but their useas shelter for troops may be hazardous and isseldom practicable. Most mines will not with-stand the effects of heavy surface bombard-ment. Coal mines are especially unsuitable fortroops or storage. Coal is structurally unstable

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.

';- - ~ - I

_ _


and requires extensive supports even in ordi- i. Access road and turn around availability.nary mining operations. Many varieties of coalgive off a gas known as fire damp or marsh gas.This is highly flammable and highly explosivewhen mixed with air. Coal dust and air alsoform an explosive mixture. Some mines,particularly salt mines, may be utilized for thestorage of supplies and equipment. Adit mines,with their horizontal or slightly inclined en-tries, are more suitable than vertical-shaftmines for underground storage. The latter typemay present drainage problems and offers moredifficulties in transporting loads into and outof the mine. To prevent their use by the enemy,mines can be flooded or destroyed with ex-plosives. The possibility of mines being usedas headquarters for guerrillas must be con-sidered, and inactive mines in a tactical areashould be blocked, destroyed, or otherwisesecured against occupancy.

110. Information Requirements - MinesThe information about a mine required for

a terrain study will depend upon the purpose.Such information as the following usually isrequired:

a. Location and name of mine.

b. Product (Mineral extracted, quality,quantity, underground and in reserves).

c. Extraction methods (deep, placer, strip,special methods).

d. Details of layout and operation.

(1)(2)

Pits, shafts, galleries, wells.Hand and mechanical labor involved.

(3) Above ground structures, plant, andequipment.

(4)(5)(6)

Refining processes.Storage facilities.Transportation facilities.

(7) Utilities (ventilation, electric power,lighting, water, firefighting).

e. Physical condition of installations andequipment.

f. Safety and security features.

g. Availability of labor.h. Any major repairs needed for operation.

111. Quarries and Pitsa. Quarries. A quarry is a site providing rock

that is suitable in quality, quantity, and sizefor construction purposes. A hardrock quarryfurnishes rock such as granite, limestone, orsandstone, which must be drilled and blastedin quarrying and which must be crushed forsome uses. Igneous and metamorphic rocks aregenerally considered hard rocks. A soft-rockquarry furnishes material that can be removedreadily by earthmoving equipment. Soft coral,caliche, shale, chalk, and tuff are materialsof this type. Sedimentary rocks are generallyconsidered soft. Quarries are generally theopen-faced type, with the vertical surface ofthe rock exposed. Depending upon local condi-tions, they may be developed by the single ormultiple bench method. A single-bench quarryhas the entire floor on one level, the height ofthe bench worked in one operation varyingfrom 2 to 30 meters (8 to 100 feet). A multiple-bench quarry is one having a series of ledgesor terraces resembling steps.

b. Pits. A pit is a site where earth or rockparticles suitable for engineer constructionmay be obtained in quantity. A borrow pit isa site providing soil suitable for fills, surfacing,or blending that can be removed with earth-moving equipment. A gravel pit consists pre-dominantly of particles of gravel size. Unsort-ed gravel from pits is used extensively forsurfacing secondary roads, in base courses forpavements for roads, taxiways, and runways,and as aggregate in concrete and bituminousoperations. An alluvial gravel pit derives itsname from the origin of the deposit, sincethe material is stream-deposited. The gravelobtained from these pits usually is very cleanand free from clay and humus. It is thereforeparticularly desirable for concrete and bit-uminous work. A bank or hill gravel pit pro-duces a clayey gravel or clayey sandy gravel.These materials are very desirable for surfac-ing work because of their binding qualities.

c. Military Considerations. Pits and quarriesare important chiefly as sources of materialsfor engineering construction. They may be localobjectives in tactical operations, if plans re-quire extensive engineering development of

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the area. Individual pits and quarries usually the manner of loading, number ofcan be bypassed by advancing forces, but anarea containing a number of them may presentdifficulties to the movement of larger units andwill tend to analyze movements. Flooded quar-ries are a particularly hazardous obstacle. Pitsand quarries provide a varying degree of coverfor troops. They may also furnish defiladedlocations for artillery and missile positions.

trucks that can be loaded at one time,access road, and turnarounds.

b. Pits.

(1)(2)

(3)

Location.Nature of source.Nature of raw materials; quality,quantity.

112. Information Requirements -Quarriesand Pits

a. Quarries.

(1) Location.(2) Nature of stone.(3) Actual and potential capacity in un-

crushed stone.

(4) Capacity of crushing machinery instone of various sizes.

(5) Details of machinery.

(6) Loading facilities(7) Amount of crushed stone that can be

hauled away in a day, considering

Section V.

113. Size, Form, and Componentsa. Description. Airfields range in size and

function from short landing strips consistingof little more than a cleared area suitable forlight liaison planes or helicopters to large per-manent air bases with many complex sup-porting installations. The simplest form of op-erational airfield consists essentially of a run-way, usually oriented in the direction of pre-vailing winds; one or more perimeter taxiways,with warmup aprons located where they jointhe ends of the runway; and hardstands to ac.commodate one or more groups of aircraft. Therunway may or may not be surfaced. In addi-tion, there will be a minimum of other facili-ties, such as access and service roads, fuel stor-age, ordnance storage, and a control tower. Theparticular characteristics will depend upon thetype of aircraft that will use the field.

b. Tactical Airfield. A tactical airfield in atheater of operations includes the followingmajor elements:

(4) Amount, depth, and type of over-burden.

(5) Drainage; ground-water level; stand-ing water.

(6) Utilities available (electricity,water).

(7)(8)

(9)(10)

(11)

Equipment available.Method of extraction (hand labor,machinery, dredging).

Method of cleaning and sorting.

Daily production capacity.

Transportation routes; access roads;surfaces of roads.

AIRFIELDS

(1) Landing strips.(2) A system of hardstands and runways.(3) Warmup aprons close to one or both

ends of the runway.

(4) Operation facilities, including controltower and operations and briefingrooms.

(5)(6)

Fuel storage and dispensing facilities.Ammunition storage facilities.

(7) General supply storage facilities.(8) Repair and maintenance facilities for

aircraft, accessories, and automotivevehicles.

(9) Roads, walkways, communications,firefighting unit, and other servicefacilities.

(10) Security and safety installations.

114. Terraina. Location. The general location of a pro-

105


posed airfield is indicated by the Air Force corm- water are required in both the con-mander or the Army aviation officer, as ap-propriate, while the exact site is chosen in co-ordination with the engineer after a carefulevaluation of the terrain.

b. Selection. In selecting a site, the follow-ing factors should be considered:

(1) Adequate dimensions to meet operat-ional requirements, with room forfuture expansion.

(2) Accessibility to supply routescommunication facilities.

and

(3) Obstructions along flightways andapproaches, including critical topo-graphical features, such as high hillsor mountains. High tension wires,roads, and railroads crossing the flightway near the runway are dangerousmental and physical hazards to pilots.

(4) Meteorological conditions (wind, rain-fall, fog, snow, frost action).

(5) Drainage.

(6) Topography. A site with favorabletopography is one located on highground with sufficient slope fornatural cross drainage as well as long-itudinal drainage and a reasonablysmooth surface requiring little earth-moving.

(7) Clearing, grubbing, and stripping re-quired. A large open area surroundedby sufficient covered areas to concealall activities is ideal. Ground coverin areas adjacent to the flight strip isespecially desirable to provide naturalconcealment for parked aircraft,dumps, and bivouac and other instal-lations.

struction and operation of airfields.(11) Camouflage requirements. A desirable

site is one that avoids identifyinglandmarks and affords cover for in-stallations and aircraft at dispersedlocations.

115. Information Requirements - AirfieldsBased on available reports and files, detailed

studies of particular airfields in local areas willbe prepared by intelligence personnel. Pertinentinformation to be included in a terrain studyshould include the following:

a. Location (map coordinates, elevation, dis-tance and direction from nearest city or town,principal landmarks, name if any).

b. Category (emergency landing strip, re-fueling and rearming strip, fighter field, bomberfield, heliport, and civilian secondary airport).

c. Characteristics of site (type of terrain,character of soils, special aspects of weatherand terrain differing from country-wide or re-gional conditions).

d. Detailed layout (sketch) of runways, tax-iways, parking and service areas.

e. Runways.

(1) Identification.(2) Length of runway and overrun; ex-

(3)(4)

tensibility.Width of runway, overrun, shoulders.Type and depth of surfacing and base.

(5) Type and adequacy of drainage(ditches, subsurface drains).

(6) Load capacity (in pounds, or kilo-grams or aircraft type).

(8) Soil characteristics. The type of soildetermines the type of equipment re-quired for construction, drainage, ef-fects of adverse weather, and the sub-grade bearing capacity that can be ob-tained.

(9) Availability of gravel, sand, coral, orother materials for excavation.

(10) Water supply. Large quantities of

(7)(8)

Gradient.Present condition.

f. Taxiways and parking (dimensions, typeand depth of surface material and base, loadcapacity, condition).

g. Detailed description of operation area;improvements planned or under construction.

h. Facilities.

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(1) Buildings (type, material, dimen- (3) Rainfall (average by months; wetsions).

(2) Maintenance and repair(number andextent of buildings and numbers andtypes of equipment used for airfieldmaintenance.

(3) Fueling (number and capacity oftanks, above or below ground).

(4) Electricity supply.(5) Water supply.

i. Related transportation (railroad, road,water; details about type, location, and ca-pacities of transportation facilities available).

]. Airfield construction sites.(1) Topography.(2) Wind (direction, intensity of pre-

vailing wind; local peculiarities).

seasons; intensity, duration, and fre-quency of rainfall).

(4) Other aspects (temperature varia-tions, storms, fog, and ground haze).

(5) Availability of local constructionmaterials.Water supply.Clearing and grading required.Drainage conditions and required im-provements.Soil classification.Flight obstructions.Frost heaving, permafrost, flooding,extremely strong winds bear directlyon airfield site construction and main-tenance.

(6)(7)(8)

(9)(10)(11)

Section VI. WATER TERMINALS

116. PortsWater terminals (ports) may range in size

from beaches suitable only for landing craftto giant complexes extending along manymiles of coastline. They usually constitute keyterrain features and primary objectives in mil-itary operations. FM 55-51 gives detailed in-formation about the organization and opera-tions of water terminals. Normally, majorwater terminals (fig. 49) are characterizedby deep harbors protected from storms andfree from ice in the winter months. The railand road networks of the area usually extendfrom the terminals inland to developed por-tions of the country. Large terminals are oftensurrounded by commercial, industrial, andshipbuilding areas.

117. Military Significance

a. Vulnerability. Large water terminals arehighly vulnerable to attack by nuclear weap-ons. When the enemy has a nuclear weaponcapability, logistical support is providedthrough a number of dispersed small termi-nals, often little more than beaches developedto meet minimum requirements. Terrain stud-ies should include an evaluation of all suitablelocations for such terminals, indicating theirphysical characteristics, relative usefulness,

and estimated capacities. A large-scale am-phibious operation may include a number ofseparate secondary landings to secure beachesthat are suitable for dispersed logistical ter-minals.

b. Evaluation. Information about estab-lished water terminals usually is contained interrain studies prepared at the highest eche-lons, which form the basis for studies used inspecific operations. The existing water termi-nals are evaluated as to their usefulness andtheir present physical condition. If an enemy-held terminal is to be used by friendly forcesafter its seizure, particular attention is givento the essential structures and facilities thatshould be spared from destruction, if prac-ticable, during the preliminary bombardmentand assault.

118. Information Requirements - WaterTerminals

The information about a water terminalwhich is most essential in preparing a terrainstudy will depend upon the features that areof the greatest concern in a specific operation.Detailed information requirements for waterterminals are contained in FM 55-8. Informa-tion required may include-

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Figure 49. Typical large water terminal (port).

a. Name, location by map references andcoordinates.

b. General characteristics (open roadstead,partly inclosed bay, landlocked harbor, shel-tered area behind a barrier reef, and river).

c. Entrance and approach channels (con-trolling depth, length, width).

d. Breakwaters (position, length, construc-tion).

e. Description of harbor.

(1) Type.(2) Harbor and channel depths.(3) Extent of silting.(4) Nature and frequency of mainte-

nance dredging.

(5) Location and nature of anchorages.

(6) Underwater obstructions.

(7) Pilotage information.

f. Bridges regarded as shipping obstruc-tions (location, type, horizontal and verticalclearances at mean low water).

g. Hydrographic and weather conditions.

h. Adjacent beaches usable by landing craft(location, length, type, gradient, and accessi-bility).

i. Cargo-handling facilities.

(1) Wharves, piers, and quays (type,function, structural features, cargo-handling machinery, road and rail-road connections, utilities, mooringfacilities).

108


(2) Wet docks and semitidal basins. (5) Open storage (location of suitable(3) Mechanical handling facilities.(4) Harbor-service craft (type, function,

number).

j. Repair facilities.(1) Repair yards.(2) Graving docks.(3) Floating docks.(4) Marine railways.

k. Storage facilities.(1) Location, type of commodities stored,

type of constructions, capacity, trans-portation connections, fire protection,special handling equipment.

(2) Cold storage facilities (temperature,daily ice making capacity).

(3) Grain storage facilities.

(4) Bulk liquid storage (capacities inbarrels).

areas, rail and road connections, ap-proximate capacity).

(6) Petroleum and coal storage (location,type, capacity, bunkering facilities).

(7) Special storage facilities for explo-sives and ammunition.

1. Clearance facilities (rail lines, highways,inland waterways, pipe lines).

m. Water supply (availability,method and rate of supply).

quality,

n. Electric power and lighting (availability,source, and characteristics of current).

o. Capacity of the terminal as a whole, underboth normal and present conditions.

p. Data needed for major repairs and im-provements; vacant areas available for ex-pansion.

q. Availability of trained, reliable person-nel.

Section VII. HYDRAULIC STRUCTURES

119. Typesa. Flood Control. The principal structure

employed in flood control is the artificial levee,an embankment built along a river course toprevent flooding of the adjacent country dur-ing high water. It may be 6 meters (20 feet)or more in height, and usually is made bypacking layers of earth upon a foundation,with grass planted on top of the levee to holdthe soil. The levee may be faced with concrete.Usually an artificial levee is constructed somefeet in rear of the river banks to provide awider channel during flood periods.

b. Dams. Earth dams for reservoirs fre-quently are built of layers of homogeneous ma-terial with a center core of puddled clay orother impermeable material. Usually the innersurface is paved with stone or concrete as aprecaution against erosion, and the outer sur-face is covered with grass to bind the surfaceand to protect it against the weather. Damsacross rivers and deep ravines, or where thereis considerable width and height, usually are

made of stone masonry or concrete. They arebuilt either straight across the river or in theform of an arc, the convex side fronting thestream (fig. 50).

c. Reservoirs. A reservoir is a wholly orpartly artificial lake used for water storage.Types of reservoirs include those for flood con-trol, irrigation, recreation, power production,and navigation. Reservoirs are utilized formunicipal water supply systems, on rivers toaid in flood control, on canals to maintain thewater level for navigation, and in hydroelec-tric installations to insure a constant watersupply. The reservoir may have a lining ofclay or other impervious material to preventwater seepage. The embankments or retainingwalls may be of earth, loose rock, or masonry.Distributing reservoirs in municipal water sys-tems sometimes are built of masonry or rein-forced concrete. They serve to take care offluctuations in demand and as a reserve in caseof interruptions at the source. In reservoirswith earth embankments, overflow is providedfor by a waste weir or canal, to carry off sur-

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Figure 50. Downstream face of Shasta Dam (California).

plus water. When the reservoir is formed by amasonry dam across a river, the surplus watermay be allowed to flow over the top, or spill-ways may be provided (fig. 51).

d. Locks. The dominant feature of developedwaterways is the canal lock. A lock is an en-closed stretch of water with a gate at eachend used to raise or lower vessels from onewater level to another. When a vessel is to passfrom a low level to a higher one, the water inthe lock is lowered until it is level with thatin which the ship is floating. The vessel ismoved into the lock and the gate is closed.Water is then allowed to enter the lock untilit reaches the higher level, and then the gateat the other end is opened and the vessel passesthrough. This procedure is reversed when the

vessel goes from a higher to a lower level.Many locks have an intermediate set of gatesso that only part of the lock is used for smallervessels. Usually the water passes through cul-verts built into the lock walls and is con-trolled by sluice gates powered by hydraulicor electric power. Lock gates are made ofeither steel or wood. A pair of gates meets inthe center of the lock entrance. When closed,the gates form an arc with the convex sidetoward the pressure of the water. The lift of acanal lock may be 12 meters (40 feet) or more.

e. Polders. Areas with an extensive networkof canals, drainage ditches, and levees maycreate a major problem in operations. Themost notable of these areas are the polders ofBelgium and The Netherlands, which have

110


Figure 51. Spillway, storage dam (Bartlett Dam, Arizona).

been reclaimed from the sea by artificiallevees called dikes. The terrain is traversed bynumerous canals and basins that drain the ex-cess water and serve as navigation routes. Thesurplus water empties into the sea at low tide.In places where the water courses lead from theinterior to the sea, they may be caused to over-flow, creating a practically impassable obstacleto movement. In the interior, the poldersgreatly limit the landing areas suitable for air-borne and airmobile forces. When the dikes aredestroyed, the cultivated areas are inundated.In these areas tanks and vehicles bog down,there is no cover for infantry, and the wateris too shallow for boats.

120. Military Importance

The military importance of hydraulic struc-tures arises from the extensive flooding thatmay be caused by their destruction. Vast areasmay be inundated by the destruction of a largedam or the artificial levees along a major river.Releasing the waters of even a small dam mayflood sections of roads and railways or increase

the width and velocity of a stream so that cross-ing operations are impeded. Hydraulic struc-tures in enemy territory may be destroyed byaerial bombardment so as to cause these effects,so they may be seized by airborne forces be-fore the enemy can demolish them. Hydraulicstructures are vulnerable to sabotage and guer-rilla action. Those in territory under friendlycontrol must be carefully guarded and subjectto strict security precautions.

121. Information Requirements - HydraulicStructures

The type of information that is requiredconcerning a particular hydraulic structurewill depend upon whether plans call for itsdefense, seizure, destruction, or reconstruction.Usually technical specialists are employed toprepare detailed studies of each structure thatis being considered. In general, basic informa-tion includes-

a. Location and name.b. Function: navigation, power, flood con-

trol, irrigation, water supply.

111


c. Construction features: design type, mate-rials, height, width, mechanical equipment,capacity.

d. Extent and nature of repairs necessary.

e. Security requirements.

f. Effects of destruction upon the surround-ing area.

Section VIII. URBAN AREAS AND BUILDINGS

122. Urban Areasa. Description. An urban area is defined as a

concentration of structures, facilities, and pop-ulation which forms the economic and culturalfocus for some larger area. Usually the in-habitants do not depend upon agricultural ac-tivities for their basic economy. A city or townmay have a number of functions that make itsignificant. It may be primarily industrial,commercial, or recreational; the headquartersof government institutions; a port or railwaycenter; or the location of an important cul-tural feature, such as a cathedral, university,or historical landmark. A large urban areausually has a metropolitan area that includesvarious surrounding settlements or suburbswhose daily economic and social life is con-nected with or influenced by the city. Intelli-gence concerning an urban area covers its gen-eral description and importance; physical char-acteristics; external communication; servicesand utilities; and major industries, includingstorage facilities.

b. Topography. The topography and geologyof the urban area and its environs are signifi-cant elements in the terrain study. Topographyexerts a major influence upon the size and pat-tern of the populated area; the location of ex-ternal communications; the possibility of in-undation or other natural disaster; and thedefense that can be made against possible land,waterborne, and air attacks. The developmentpattern of an urban area is the physical adjust-ment of the area to its topography, as influ-enced by past events, current economic forces,and social trends.

c. Construction. The elements comprising anurban area may be classified according to thepredominant construction and function of thebuildings and other structures. Where no gapsexist between buildings, as in the businessdistricts of larger towns and cities, this is de-scribed as block type construction. Detached

and semi-detached building areas are thosewhere the buildings are spaced relatively closetogether, as they are in low- and middle-costhousing areas. Isolated housing areas arefound on the approaches to towns and citieswhere individual or small groups of homes arelocated in the midst of large open areas. Thisis typical of the suburbs of the average city.

d. Functional Areas. Normally a city in-cludes separate areas largely devoted to onetype of use. The major functional areas maybe distinguished as follows:

(1) Industrial areas comprise a groupingof individual plants and loft build-ings, with associated storage andtransportation facilities, devoted tomanufacturing activities.

(2) Commercial areas are composed of aconcentration of retail and wholesaleestablishments, financial institutions,office buildings, hotels, garages, publicbuildings, and light manufacturingplants.

(3) Residential areas consist predomi-nantly of dwellings with interspersedshopping centers; churches; schools;and fire, police, telephone, and powerstations.

(4) Transportation and storage areascontain the terminal, transshipment,storage and repair facilities and serv-ice buildings associated with generalmovement by rail, water, road, pipe-line, or railway.

(5) Governmental-institutional areas in-clude the grounds, structures, andfacilities related to governmental ad-ministrative offices, hospitals, schools,colleges, homes for the aged or or-phans, sanitariums, monasteries,penal or research institutions andsimilar establishments which usually

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form distinctive and generally exten-sive areas.

(6) Military areas contain structures andfacilities for billeting, quartering, de-fense, hospitalization, storage, andrepair, which are devoted exclusivelyto military use.

(7) Open areas comprise land not occu-pied by buildings and not assigned toany industrial, transportation, busi-ness or residential activity. Developedopen areas include cultivated land,parks, recreation areas, and ceme-teries. Undeveloped open areas in-clude swamps, woods, beaches, andother vacant land.

123. Military Considerations

a. Use of Urban Area. The decision to by-pass or to seize and occupy an urban area de-pends upon the mission of the unit concerned.Cities and towns may be important objectivesbecause they represent centers of population,transportation, manufacture, and supply. Portcities and railroad centers are given a prioritystatus as targets and objectives in both tacticaland strategical planning. Unless the missionrequires otherwise, a city or town usually isbypassed and isolated, since it is an obstaclethat canalizes and impedes both attacking andcounterattacking forces. Urban areas are vul-nerable to destruction by air or artillery bom-bardment and may be neutralized by chemical,biological, or radiological contamination. Firesstarted by nuclear weapons or incendiariesmay make them untenable. Combat withinbuilt-up areas is described in detail in FM31-50.

b. Limited Observation and Fields of Fire.Because the opposing troops usually are closeto each other, effective close support by artil-lery and combat aviation is limited. The avail-able cover is rigid and set in straight lines, sothat all movement in the open usually can beobserved unless it is concealed by smoke, dust,or darkness. Smoke may be used to provideconcealment, limit observation, and achieve de-ception and surprise. In a built-up area, smokeremains effective longer than in open areas. Itis usually difficult to observe and locate enemy

weapon positions because of the dust causedby the impact of projectiles and explosivecharges and the smoke from explosions andfires.

c. Increased Cover and Concealment. Weap-ons and troops may be concealed in built-upareas, and ample cover is usually availableagainst small-arms fire. Cover from air andartillery bombardment, however, is providedonly in buildings of particularly substantialconstruction.

d. Movement. The mobility and maneuver-ability of infantry, artillery, and armor aregreatly limited in built-up areas. Vehiculartraffic is canalized, and extremely vulnerableto ambush and the close-range direct fires ofenemy weapons.

e. Communications. It is difficult to maintainefficient communications in built-up areas.Normally control must be decentralized tosmall-unit commanders. Tall buildings andthose with steel frames may interfere withradio communication. Reliance usually must beplaced upon wire and foot messengers.

f. Attack. Detailed information concerningthe enemy, his defenses, the terrain surround-ing the urban area that is under his control,and the layout of the built-up area is essentialto the commander in making plans and deci-sions for an attack. Particular emphasis isplaced upon determining the location of cov-ered approaches to the urban area, the locationof public utility plants and their securitymeasures and the location and nature of allobstacles. The objective of the attacking forceis to seize the entire urban area. Within thearea the objectives for individual units includekey installations such as railroad stations, tel-ephone exchanges, and the public utility plants,which are often organized as centers of enemyresistance. The attack on an urban area beginswith the seizure or terrain features which dom-inate approaches to the city, followed by theseizure of buildings on the near edge to reduceor eliminate the defender's observation and di-rect fire upon the approaches. The last phaseis a systematic advance through the area untilit is fully secured.

g. Defense. Urban areas favor the defense.Whether or not a city or town is organized for

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defense depends upon its size, relation to the (4) Landmarks (natural and manmade).general defensive position, and the amount ofcover it offers for occupying forces. Cities,towns, and villages constructed of flammablematerials provide little protection and may be-come a hazard to the defender, and buildingsof solid masonry can be developed into well-fortified defensive positions or centers of re-sistance. Cellars, sewers, subway tunnels, thickmasonry walls, and reinforced concrete floorsand roofs provide cover for the defender dur-ing heavy bombardments. A heavy aerial orartillery bombardment of a city before an at-tack actually may serve to strengthen its de-fenses. The fallen rubble may give the defenderincreased protection, and may make the streetsimpassable for armor.

124. Information Requirements-UrbanAreas

Information about an urban area requiresthe compilation of many factors, each devotedto a particular aspect of the area, such as thetransportation services, utilities, billeting fa-cilities, or industries. A terrain study shouldinclude annotated maps, plans, and photo-graphs, with an accompanying text giving thatwhich cannot be shown graphically. Informa-tion that should be included under each cate-gory is outlined below. The scope of the in-formation that is presented is limited by thepurpose for which the study is being prepared.The text should include information in thefollowing categories, as pertinent:

a. Description.(1) Name and location (geographic and

grid coordinates).(2) Population (number and trend, sig-

nificant ethnic and religious seg-ments).

(3) Principal function (communicationsand industry).

b. Physical Characteristics.(1) Topography and geology of area and

environs.(2) General cross-country movement of

environs.(3) Climate (mean temperatures and

rainfall).

(5) Extent of built-up areas (presentboundaries, recent additions, prob-able future expansion).

(6) Functional areas.

c. Structures.

(1) Characteristics of predominant typesof buildings (height, number of stor-ies, principal construction materials).

(2) Structure density (ratio of roof cov-erage to gross ground area; as war-ranted, ratio of roof coverage toground area within each of the func-tional areas).

(3) Principal buildings.

d. Susceptibility to Fire and Shock.

e. Damaged or Destroyed Areas (delinea-tion and general character).

f. Significant Ethnic and Religious Group-ings (delineation and general character of theareas occupied).

g. Streets.

(1) Surface, condition, and pattern.

(2) Prevailing widths (to curb and build-ing to building).

(3) Names and alinement of throughroutes and principal streets.

(4) Location and characteristicsbridges, tunnels, and ferries.

of

h. External Communications.

(1) Roads. Identification of the roads thatenter the urban area, the routes thatbypass it, and the road distances tothe nearest important town on eachroute should be shown on maps. Inthe text, the importance of the roadsas avenues of movement to and fromthe town should be discussed. Anno-tations on city maps should locate andidentify highway structures, ferries,and road service facilities.

(2) Railways. Maps should show the rail-ways that enter or bypass the urbanarea, with distances to the nearest

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important towns. Text should discussthe importance of the railways astransportation arteries. Annotationson city maps should locate and iden-tify railway structures and crossings(bridges, tunnels, and ferries) andsuch railway structures as passengerand freight stations, yards and sid-ings, repair shops, turntables, and"y" track.

(3) Inland waterways. Identification ofeach navigable water route (river,lake or canal) which borders orpasses through the urban area andthe waterway distance to the nearestupstream or downstream port shouldappear on maps. The importance ofthe waterway should be discussed inthe text. Annotations on city mapsshould locate and identify importantwaterway structures. Information onshipyards is included with that on theindustries of the urban area.

(4) Airfields. The location of each airfieldand seaplane station which serves theurban area should be shown on citymaps or, if beyond the limits of thecity, on topographic maps. Textshould indicate the adequacy of theexisting air service, list each com-mercial airline which serves the area,and provide information on the fre-quency of service. Information aboutairfield classification is presented inTM 5-330.

i. Urban Services and Facilities.(1) Water supply.

(a) Sources (name, location, type, ca-pacity).

(b) Treatment plants (number, type,capacity, and location).

(c) Storage (name, location, type, ca-pacity).

(d) Method of distribution.

(e) Consumption (in terms of mini-mum and average requirements perperson per day, whether any ra-tioning is practiced and duringwhat periods, annual consumption).

(2) Sewage disposal (sanitary, storm, in-dustrial waste).

(a) Collection methods (type, ade-quacy).

(b) Treatment plants (type, location).(c) Disposal methods (including loca-

tion of dumps or incineratingplants).

(3) Garbage and trash disposal.(a) Collection methods.(b) Treatment plants (type, location).(c) Disposal methods (including loca-

tion of dumps, incinerators, andprocessing plants producing ferti-lizer).

(4) Major hospitals.(a) Name, location, and specialization,

if any.(b) Bed capacity.(c) Age and condition.

(5) Electricity.(a) Sources (name, type, location, in-

stalled capacity).(b) Substations (name, type, location,

capacity).(c) Distribution current characteris-

tics.(d) Number of consumers.(e) Yearly consumption.

(6) Gas.(a) Type.(b) Sources (name, location, capacity).(c) Storage (type, location, capacity).(d) Extent of distribution.(e) Number of consumers.(f) Yearly consumption.

(7) Storage.(a) Open (large open areas within or

adjoining the town suitable for useas open storage and supply dumps).

(b)(c)

Covered (warehouses and sheds).Cold (refrigerated storage; iceplants with cold-storage facilities).

(d) POL (number of tanks or reser-voirs at each location; capacities inU. S. barrels).


(e) Explosives (magazine and bulk-storage facilities; types and quan-tities of explosives stored).

(8) Ice-manufacturing plants (name, lo-cation, capacity).

(9) Billeting and accommodation. (Totalcapacity for billeting and accommoda-tion in military barracks, hotels, pub-lic buildings, school and institutionalbuildings, and other structures; totalcapacity of bakery and laundry estab-lishments; availability of baths andswimming pools suitable for troopuse. Location, capacity, and type ofeach structure.)

(10) Internal transit system (type, extent,location of main terminal, and main-tenance facilities).

(11) Fire protection (organization andmanpower of fire department; quan-tity and type of equipment).

(12) City government (type, personalities,location of facilities).

(13) Civil defense (organization and man-power; quantity and type of equip-ment).

(14) Industry.(a) Major industrial activity (for each

industry, the type, number ofplants, number of employees, andimportance) .

(b) Significant manufacturing plants.

125. Buildingsa. Construction. The design and construc-

tion of buildings are influenced by climate,available materials, function, and the culturaldevelopment of the native inhabitants. In areaswith a tropical climate and primitive agricul-ture, for example, buildings usually are onlycrude huts made of woven grass, sticks, andmud. Buildings in desert oases are made ofclay with thick walls, so that they are cool insummer and fairly warm in winter. In dryclimates, where suitable timber is scarce, awooden structure is a rarity and buildings areconstructed from stone, adobe clay, or turf.Where there are cold winters, buildings will besolidly constructed of stone and wood.

b. Military Considerations. The military sig-nificance of a building or group of buildingsdepends upon the purposes of the study. Abuilding may have value as an obstacle, a de-fensive strongpoint, or as a possible storage,headquarters, medical, or maintenance instal-lation. The structural features of buildingscomprise the predominant materials used, sizeand height, fire resistance, and architecturaldesign. Brick, stone, and masonry buildings,when demolished, create rubble that may makeformidable obstacles, or may provide conceal-ment and cover for troops. Flimsy woodenbuildings are highly flammable and may beremunerative targets for incendiary shells andbombs. Since the fires are an obstacle to an at-tacker, they may be employed as a weapon bythe defender. The height and number of storiesin a building are significant features whenselecting observation points. Buildings used inthe community may be adapted for militaryuses. These include garages and other repairfacilities, stadiums, theaters, auditoriums,warehouses, transportation terminals, andschools. Wherever possible, structures of re-ligious or artistic importance are usually desig-nated before an operation by civil affairs/mili-tary government agencies, and their employ-ment for military purposes is prohibited.Buildings made of solid masonry, concrete, andsteel may be organized into defensive strong-points. Substantial structures with deep base-ments provide varying degrees of cover fromair or artillery attack. The protection againstnuclear effects offered by buildings varies ac-cording to the type of construction, flamma-bility, distance from ground zero, and manyother factors. Personnel in buildings will beprotected from the thermal radiation effectsof a nuclear weapon and will receive some de-gree of protection from nuclear radiationeffects. Casualties from secondary blast effectsare caused largely by falling walls and ceil-ings and flying glass.

126. Information Requirements-Buildings

a. Location and function (residence, store,warehouse, factory, school, government head-quarters, and communication center).

b. Structural features (materials, founda-

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tions, roof, bearing capacity of floors, exits, and the amount of military equipment thatand basement).

c. Layout and capacity (floor plans, areas,cubages).

d. Utilities.

e. Possible military uses.

f. Security features (estimated capabilityfor withstanding bombardment by conven-tional and nuclear weapons).

g. Needed repairs or improvements formilitary use.

127. Utilitiesa. Special Studies. Detailed intelligence

about the utilities of an urban area is neces-sary in order to plan its utilization for mili-tary purposes. In addition, civil affairs mayrequire specific, detailed information and in-telligence for special purposes. Special studiesby technical personnel should be prepared cov-ering each of the following:

(1) Water supply.(2) Sewage disposal.(3) Electric power.(4) Illuminating gas.(5) Public transportation system(6) Communications.(7) Fire protection.(8) Trash and garbage disposal.

b. Use of Special Studies. Intelligence stud-ies covering utilities form the basis for esti-mating requirements for operating and main-tenance personnel, the equipment and replace-ment parts needed for repairs and operation,

must be provided to supplement the existingutility installations. These studies also furnisha guide to selecting the most profitable targetsfor air attack. The destruction of key utilitiesis given a high priority in planning aerialbombardments, since a breakdown in theseservices results in disorganization of the en-emy defenses and is highly damaging to civil-ian morale.

128. Information Requirements-UtilitiesThe amount and type of information about

the utilities of an urban area that is requiredwill depend upon the purpose for which thearea is being considered. If it is intended todevelop a city into a major logistical base,complete information concerning the capacity,state of repair, and operating methods of eachutility will be nceessary. The capability to sup-ply minimum civilian needs as well as militaryrequirements must be evaluated. General sur-veys of utilities should include the followinginformation about each service or installa-tion-

a. Physical condition.

b. Adequacy for normal load.

c. Portion of present capacity that could bediverted to military use.

d. Repairs, essential for military utilization.

e. Safety and security provisions.

f. Availability of skilled, reliable, civilianpersonnel.

g. General efficiency and dependability ofthe plant or system.

Section IX. NONURBAN AREAS

129. Typesa. Farmstead. Populated areas outside towns

and cities usually consist of farmsteads andsmall settlements. A farmstead is the dwellingand adjacent buildings associated with an in-dividual farm. The characteristics of a farm-stead reflect the climate of the area and thetype of agriculture.

b. Tropical Climate. In rainy tropical cli-

mates, most of the inhabitants dwell alongstreams and waterways, the settlements beinglocated on the bluffs, which are well-drainedand exposed to the river breezes. The largerubber, coconut, or banana plantations are usu-ally near the ocean or on the banks of naviga-ble rivers, since roads and railways are fewand difficult to maintain. Nonurban areas indry subtropical climates are dominated bylarge cattle and sheep ranches, with individ-

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ual farmsteads separated by miles of grazing quarters and other facilities for large numbersland. In semiarid tropical climates, the nativeagriculture is largely pastoral, and the rela-tively few settlements consists of huts sur-rounded by mud walls or fences of thornybrush. Subarctic villages seldom consist ofmore than a dozen dwellings, with as much as50 to 65 kilometers (30 to 40 miles) betweensettled areas.

c. Temperate Climate. In temperate climates,the buildings of a farmstead are detached fromeach other, while in areas with extremely coldwinters the house, barn, and other outbuildingscommonly are under one roof. The outbuildingsof a farmstead in the tropics normally are fewand small, because the animals remain out-doors all year. Small villages in the middlelatitudes often consist of houses built in rowsalong the sides of a road or clustered aroundan open square, and in tropical climates thehouses of a village usually are dispersed with-out any regular pattern.

130. Military Significancea. In general, the same considerations that

are pertinent to an urban area also apply tononurban areas. Small settlements may becritical when they dominate routes of commu-nication at fords, bridges, railway lines, ordefiles (fig. 52). Villages that are small insize may have considerable military signifi-cance because of a particular industry, mine,or other unique economic feature. They maybe local markets and distribution centers serv-ing a wide area and representing an importantenemy source of foodstuffs and other supplies.A village with a small local population may bea resort area or the site of a university orsimilar large institution, capable of providing

of troops.

b. In tactical operations, it is occasionallynecessary to secure or destroy small villagesthat have no direct military value but are usedto provide concealment, supplies, and othersupport to guerrillas. The civilian inhabitantsmay have to be relocated in other settlementsunder military control. The buildings of afarmstead furnish quarters for troops andshelter for storage and maintenance facilities.Stone buildings may be suitable for weaponsemplacements and defensive strongpoints.Nearly all rural dwellings are within a shortdistance of a reliable source of water. Cross-country movement frequently is hampered byobstacles such as stone fences, retaining walls,irrigation ditches, and paddy fields. Featuressuch as high fences, hedgerows, embankments,and ditches may offer limited cover and con-cealment to individuals and small groups.

131. Information Requirements-NonurbanAreas

The particular information about a farm-stead or small village that is required will de-pend largely upon the mission of the unitconcerned. Basic information requirementsshould include-

a. Location; relation to local terrain fea-tures.

b. Size (area, population, pattern of streetsor roads).

c. Facilities for quarters, maintenance andrepair installations.

d. Predominant construction materials.

e. Utilities.

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EL4A"II:

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CHAPTER 7

MILITARY ASPECTS OF THE TERRAIN

Section I. MILITARY USE OF TERRAIN

132. Commander's Considerations

In conducting an operation, the commandermust determine how the terrain can be usedmost effectively by his forces, how it may af-fect the enemy's capabilities, and how it maybe exploited to interfere with the enemy. Withthe assistance of his staff, he considers theweather conditions, relief and drainage, vege-tation, surface materials, and manmade fea-tures and their effects upon-

a. Key terrain.

b. Observation and fields of fire.

c. Cover and concealment.

d. Obstacles.

e. Avenues of approach.

f. Communications.

133. Key TerrainThe relative importance of various aspects

of the terrain varies with the mission, the typeof operation, the size and composition of theforces involved, and their weapons and equip-ment. Detailed intelligence concerning terrainfeatures normally increases as the size of theunit diminishes. The commander of a fieldarmy, for example, may be concerned aboutthe effects that an extensive mountain rangewill have upon a proposed campaign. A corpscommander might be interested only in onemountain of the range, while the commanderof a brigade would concentrate upon a particu-lar group of foothills in his area. When makinga systematic study of the military aspects ofan area, it is sometimes divided into naturalsubareas, or, if there are no suitable natural

boundaries, into subareas based upon the tac-tical plan. The military aspects of the terrainthen are evaluated by each subarea from boththe friendly and enemy points of view.

134. Observation and Fields of Fire

a. Observation. Observation is the direct ex-amination of terrain and military activities.It includes examination from ground and airby unaided vision or assisted by optical andinfrared devices and detection by photographs,radar, and sonic devices. In general, observa-tion refers to the ability of a force to see theenemy under specified conditions of weatherand terrain. The best terrain for observationis that which permits both long-range observa-tion into enemy-held areas and close-in ob-servation of the hostile forward elements.Usually long-range observation is found nearthe topographical crest and close-in observa-tion is obtained from a location near the mili-tary crest. Fog, smoke, precipitation, heatrefraction, darkness, manmade and naturalfeatures, and vegetation may limit or denyobservation. They must be evaluated in deter-mining the extent and type of observation thatwill be available to enemy and friendly forces.The highest point on the terrain does not al-ways provide the best observation, since varia-tions in relief often create blind spots in thefield of vision. The selection of observationpoints should be based upon reconnaissance,topographic profiles, or examination of aerialphotographs.

b. Fields of Fire. A field of fire is an areathat a weapon or group of weapons can covereffectively with fire from a given position. The

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natural terrain must be evaluated according difficult to obtain. Caves, buildings of excep-to its suitability for flat-trajectory weapons,high-trajectory weapons, rockets, and guidedmissiles, including those with nuclear capabil-ities. The ideal field of fire for flat-trajectoryweapons is flat or gently sloping terrain onwhich an enemy can be seen with no protec-tion for him within the effective ranges of thewaepons. Broken terrain creates dead spotsand furnishes cover and concealment for theenemy. Open terrain providing good fields offire permits a unit to defend a wide front.Broken terrain makes it necessary to providemore troops and weapons to defend a givenfrontage. The field of fire of high-trajectoryweapons is limited only by very steep reverseslopes that the weapons cannot reach and bymasks which permit the enemy to occupy posi-tions in defilade. Fields of fire can be improvedby cutting or burning vegetation, demolishingbuildings, and cutting lanes through woods.

135. Cover and Concealmenta. Evaluation of Terrain. Terrain is eval-

uated to insure the maximum use of conceal-ment and cover. Terrain under enemy controlis also studied, to determine how his conceal-ment and cover can be destroyed. In the attack,concealed and covered routes into the enemyposition are sought to gain surprise and toreduce casualties. In the defense, concealmentand cover are utilized not only to protect in-dividual positions, but also to hide the generaltrace of the defenses, so that the attackingtroops may be vulnerable to surprise by thelocation of defense positions and weaponsfires. When evaluating terrain for the coverthat it will provide, the characteristics of allthe weapons used by the enemy must be con-sidered. This includes their ranges, types offire, and the relative quantities of each type ofweapon available to him.

b. Cover. Topography is the major factorinfluencing cover. Valleys, mountains, gullies,ravines, hills, and similar features providecover from flat-trajectory weapons. Individualsand small units may secure cover from suchterrain features as ditches, riverbanks, foldsin the ground, shell craters, buildings, walls,railroad embankments and cuts, and highwayfills. Cover from high-angle weapons usually is

tionally strong construction, and the steepslopes of hills and mountains may offer somedegree of cover, depending upon the capabili-ties of the weapons employed by the enemy.Nuclear thermal radiation travels by line ofsight, so that it will be masked by hills, banksof ravines, and gullies. The extent of protec-tion thus provided will depend upon theheight of the explosion. A nuclear blast wavecurves around obstacles and is less affected byrelief features.

c. Concealment. Terrain features that offercover also provide concealment. The greaterthe irregularity of the terrain, the more con-cealment it will furnish from ground observa-tion. Lower echelons are concerned with theconcealment of men, vehicles, weapons, andemplacements; higher echelons, with the con-cealment of headquarters, supply dumps, air-fields, and other major installations.

136. Obstacles

a. Types. According to their effects, obsta-cles may be classified as antipersonnel obsta-cles, antimechanized obstacles, underwaterobstacles, and obstacles to the landing of air-craft. Natural obstacles comprise such fea-tures as unfordable streams, swamps, deepsnow, cliffs, steep slopes, thick woods and un-dergrowth, flooded areas, boulder-strewn areas,lakes, mountains, and nontrafficable soils. Arti-ficial obstacles include those prepared to delayor stop military movement, such as contami-nated areas, minefields, trenches, antitankditches or barriers, roadblocks, blown bridges,road craters, deliberately flooded areas, wireentanglements, and various types of beach andunderwater obstacles. They also include man-made features that were not originally de-signed as obstacles to military movement, suchas canals, levees, quarries, or reservoirs.

b. Employment. The employment of obsta-cles is integrated with the overall scheme ofmaneuver and fire support. Both natural andartificial obstacles are utilized to channel, di-rect, restrict, delay, or stop an opposing force.Instructions for the employment of obstaclesusually are included as a barrier annex to theoperation order of divisions or higher echelons.

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FM 31-10 discusses the use of obstacles and and nature. For example, a deep creek lyingthe requirements of barrier plans.

c. Barriers. A barrier plan provides for themost effective employment of obstacles to im-pede enemy movement along favorable routesof approach, divert advancing enemy forcestowards routes favorable to defense or compelthe enemy to concentrate or disperse. Artificialobstacles must not be located where theywould interfere with the proposed movementsof friendly forces or with counterattack plans.They may be placed in considerable depth, soas to provide time for counterattacking troopsto meet an enemy threat, and to force theenemy to expend time and strength at eachbarrier. To be fully effective, artificial obsta-cles must be kept under observation at alltimes, and must be augmented by fire or ex-plosives. Whenever possible, obstacles are sitedso that they are under friendly observation butdefiladed from enemy observation. Local unitcommanders are responsible for constructingobstacles for the close-in defense of their posi-tions. Advice and technical assistance is pro-vided by engineers, who also construct andinstall obstacles which require special skill andequipment. The use of toxic chemical and bio-logical agents and radiological contaminationto supplement barriers or as obstacles, makesit possible to deny or restrict areas by con-tamination, to canalize enemy maneuver, or tocontaminate enemy field fortifications so thatthey are untenable. Additional informationabout the employment of these agents is con-tained in FM 3-5, FM 21-40, and FM 100-5.

d. Effects. The effects of natural terrainfeatures as obstacles to military movement arediscussed in chapter 6. Artificial obstacles aredescribed in FM 5-15 and FM 31-10. Thelocation and extent of both natural and arti-ficial obstacles must be considered by a com-mander in making his plans. He must decidehow they will affect his mission. The tacticaleffect of an obstacle depends upon the type ofoperation, the weapons and equipment em-ployed, and the size of the forces involved. Aterrain feature that is a major obstacle for acompany may be a minor obstacle to a brigadeand no obstacle at all to a division.

e. Location. Obstacles may either help orhinder a unit, depending upon their location

across the axis of advance will slow up anattacker, but will provide defending forceswith an advantage, since it delays advancingtroops and exposes them to fire. Similarly,heavy woods in front of a position may pro-vide infantry with a concealed route of ap-proach but act as an obstacle to the movementof supporting tanks. In general, obstacles per-pendicular to the axis of advance favor a de-fending force, while those parallel to the axismay give the attacker an advantage by protect-ing his flanks, although they will also limitlateral movement and his ability to maneuver.

f. Offense. In offensive operations, obstaclesinfluence the choice of objectives, the avenuesof approach to an objective, and the time andformation of an attack. Obstacles may be em-ployed to contribute to flank security, impedecounterattack, provide additional protectionfor a section of the front that is not stronglymanned, or assist in enemy entrapment.

g. Defense. Obstacles are employed in thedefense to channel, direct, delay, or stop themovement of an approaching force. They maybe used to delay the initial enemy advancetoward the front and flanks of a position, de-lay the movements of enemy penetrating orenveloping forces, or canalize enemy penetra-tions into avenues of approach where they canbe defeated, or destroyed.

137. Avenues of Approacha. To a Terrain Feature or an Objective.

This is an area of terrain which provides asuitable, relatively easy route of movement fora force of a particular size and type. An ave-nue of approach should provide-

(1) Ease of movement toward the objec-tive.

(2) Concealment and cover from the de-fender's observation and fire.

(3) Favorable observation and fields offire for the attacker.

(4) Adequate maneuver room for the at-tacking force.

b. Suitability and Ease of Movement. Thesuitability and ease of movement of an avenueof approach depend upon-

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(1) The routes of communication. area bounded on at least two opposite sides by(2)(3)(4)(5)(6)

Soil trafficability.Concealment and cover.Observation and fields of fire.Obstacles.Relationship of terrain corridors andcross compartments.

c. Multiple Use. In some types of operations,in which maneuver is very limited by eitherweather or terrain, an avenue of approach mayin itself be a key terrain feature. For example,in rugged mountainous terrain, one road alonga valley may be the only route of supply and atthe same time thb most favorable avenue forapproach for the major element of the attack-ing force. A river in the jungle may be theonly transportation route, and thus a key ter-rain feature, an avenue of approach, and anobstacle.

d. In Attack. Usually an attack is directedtoward securing dominating terrain early inthe action. The avenue of approach that ismost favorable for accomplishing this missionnormally is assigned to the forces making themain attack. Whenever possible, the avenuesof approach that are selected are those thatavoid areas most strongly held by the enemy.In planning an attack, a study is made of theavenues of approach that might be used by theenemy for counterattacks and for reinforcingand supplying his forces. These avenues can bedetermined by an analysis of the terrain in itsrelation to the location of enemy reserves andsupply routes.

e. In Defense. In planning the organization ofdefense positions, the terrain is evaluated todetermine the avenues of approach that aremost likely to be used by the enemy. Thesenormally will be the avenues that lead towardkey terrain features, provide good observation,fields of fire, concealment and cover, and eitheravoid or exploit obstacles. Defense positions aresited to deny such avenues of approach to theenemy. The avenues of approach that can beused by friendly forces in counterattacks alsoare evaluated.

138. CompartmentsThe effects of relief and drainage upon ave-

nues of approach are considered in terms ofcompartments. A terrain compartment is an

terrain features such as woods, ridges, or vil-lages that limit observation and observed fireinto the area from points outside the area. Aterrain compartment includes not only the areaenclosed but the limiting features as well. De-limiting lines are imaginary lines drawn alonglimiting features from which ground observe-tion into a compartment is limited. In compart-ments formed by woods and villages, theselines run at some point within the edge of thewoods or village, depending upon the densityof the woods, or the number and density of thebuildings. Compartments are classified accord-ing to the direction of movement of the forcesoperating in them. They are termed corridors(fig. 53) when the longer dimension of thecompartment lies generally in the direction ofmovement, or leads toward the objective, andcross compartments (fig. 54) when the longeraxis is perpendicular or oblique to the direc-tion of movement. Compartments are alsoclassified as simple or complex (figs. 55 and56). A complex compartment is one having asmaller compartment or compartments lyingwithin it. This is the type most often encoun-tered.

139. CorridorsCorridors, or ridges that form their limiting

features, provide favorable routes of approachfor an advancing force because the defender'slateral organization and fields of flat-trajectoryfire are obstructed by the limiting features,which also decrease his ability to obtain mu-tual support between units and limit his obser-vation. To the attacker, a corridor offers twotypes of approach: valley approach and ridgeapproach.

a. Valley Approach. Although a valley ap-proach may provide concealment and cover,the military crest of the limiting features oneach side must be controlled to deny enemyobservation and direct fire into the valley. Thebest axis of advance is the one that offers themost favorable conditions of observation,cross-country movement, fields of fire, conceal-ment, and cover. Often the most favorableroute is along the slopes of a ridge below themilitary crest rather than along the valleyfloor. A valley approach should never be usedwhen the enemy controls dominant flank ob-

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Ait DIRECTION OF ATTACK

Figure 53. Terrain corridor.

Figure 54. Cross compartmnent.124


Figure 55. Simple compartment.

IIIIIIIIIIII

H

Figure 56. Complex compartments.125


servation into the valley, where there are slightly below the topographical crest, withnumerous obstacles, and the soils have poortrafficability characteristics.

b. Ridge Approach. The suitability of aridge for an avenue of approach depends uponits width and shape, the size and frontage ofthe unit concerned, the distance to adjacentridges and their elevations, and the capabil-ities of the enemy weapons. A ridge approachplaces the axis of advance along dominantobservation, but offers little protection fromenemy fire directed at the ridge. Usually thebest axis of advance in a ridge approach is

sufficient forces deployed to control the crest.c. Cross Compartments. Cross compartments

provide the defender with the most favorableterrain for obtaining maximum observationand fields of fire. Mutual support betweenunits, both laterally and in depth, is availableand cross compartments also provide the de-fender with successive defensive or delayingpositions. The concealment or cover providedby each limiting feature permits the defenderto shift his reserves to meet or to counterthreats to his position.

Section II. SPECIAL OPERATIONS

140. Amphibious Operationsa. Detailed Studies. Amphibious operations

require detailed studies of hydrography,weather, and terrain. A technical discussion ofthe requirements and preparation of thesestudies is beyond the scope of this manual.They are covered in FM 6030, FM 110-101,and FM 110-115, which also describe the char-acteristics, tactics, and techniques of amphib-ious operations. The discussion in this para-graph supplements information in paragraphs70 through 75.

b. Weather Effects. All phases of an amphib-ious operation are directly influenced byweather conditions. Weather affects the tides,beaching and unloading conditions, speeds ofvessels, air support, and visibility. Poor weath-er conditions may provide cover for the am-phibious force, but favorable weather is essen-tial for the actual landing and during theinitial buildup that follows, because excessivesea and swell jeopardize the entire operation.

c. Location. The ideal beach for an amphibi-ous landing is one near a strategic location,with no obstructions seaward; deep waterclose nearshore; a firm bottom; minimum vari-ation in tides, currents, or surf. The beachterrain should be gently rising, relativelyclear, with a firm surface that has adequatedrainage. Adequate exits from the beach areashould be available. Flat or gently rising ter-rain, backed by a coastal range high enoughto mask the landing area, is the most desirablefor landing operations. Ideal conditions arerarely found, and so suitable areas must be

evaluated to determine those that come nearestto the optimum requirements.

d. Coastal Plain. A landing on a widecoastal plain provides unrestricted maneuverroom usually free from enemy observationand a subsequent advance from the beach canbe made in any direction. Boundaries and ob-jectives are hard to locate on this type of ter-rain, however, and there are few prominentregistration points for artillery, naval gunfire,and aerial bombardment. Usually there is nogood defensive terrain on the flanks of thebeachhead, so that more troops are required toprotect the flanks.

e. Coastal Ridge. Terrain which rises evenlyto a considerable distance back from the beachgives the defender excellent observation andfields of fire. More commonly, the coastal arearemains flat for some distance and then risesabruptly to a coastal ridge.

f. Sand Dunes. Ground that is sharplybroken by extensive sand dunes or a lowcoastal plateau provides the attacker with con-cealment from enemy observation. The smallcompartments and corridors limit the range ofdefensive fires. Direction and control may beextremely difficult.

g. Mountains. Mountains located directly onthe sea usually limit the number of beacheslarge enough to accommodate a landing force ofeffective size. Where steep ground is lightlydefended or neglected by the enemy, a lightlyequipped force may seize it and gain surprise.Airborne or airmobile troops may be used toblock the movement of enemy reserves to the

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landing area, or to secure passes through the tics can land in areas that are otherwise ac-mountains and thus prevent the enemy frominterfering with the amphibious landing.

141. Airborne-Airmobile Operationsa. Basic Factors. The characteristics, tactics,

and techniques of airborne operations arediscussed in FM 17-36 and FM 57-10. Air-borne forces are capable of crossing such ter-rain barriers as inland seas, mountains, andjungles that represent serious obstacles to themovement of other troops. Usually airborne as-saults are made on terrain that is relativelyundefended, to secure initial surprise. Weatherhas greater restrictive effects upon airborneoperations than upon ground operations. Ad-verse weather may cause postponement or de-lay in initiating an operation, and preventadequate reinforcement or supply by air. Inaddition to terrain studies covering landingand drop-zone areas, special studies may berequired to determine the most favorableroutes for linkup between airborne forces andfriendly ground units.

b. Terrain Requirements. One of the princi-pal factors influencing the selection of a land-ing area for airborne forces is the terrain. Thearea chosen must provide adequate space topermit defense in depth; room for maneuver;a safe landing for troops, supplies, and equip-ment; and protection for critical installations.Airborne troops can land on any terrain thatis relatively free from obstacles. Unobstructedareas are required for the landing and recov-ery of heavy equipment dropped by parachute.Assault aircraft can land on any relativelylevel and unobstructed terrain that has suit-able trafficability. Other fixed-wing transportaircraft require suitable airfields or preparedlanding strips. Rotary-wing and other aircraftwith vertical takeoff and landing characteris-

cessible only to parachute units.c. Drop Areas. The selection of drop areas

for the delivery of supplies by parachute re-quires a consideration of the following:

(1) Length. The required length of thearea depends upon the type of planebeing used. Normally an area 460meters (500 yards) long is a mini-mum requirement.

(2) Width. A width of 180 meters (200yards) is minimum. The pilot musthave a reasonable amount of room sothat he may fly to the right or left ofthe center of the area, allowing forthe drift of his plane under the in-fluence of surface winds.

(3) Surface conditions. The type of soilmust be considered in relation to theeffect that it will have upon the fall-ing loads. A hard surface may causethe bundles to break open upon land-ing. Soil that is muddy or swampymay cause the dropped loads to burythemselves upon landing, making re-covery difficult or impossible.

(4) Topography. A clear and level areais desirable. Drop zones on a steepslope or mountainside cause the bun-dles to scatter, tumble, and breakopen. A mountain or hill top usuallyhas turbulent winds that reduce dropaccuracy and make the drift of bun-dles unpredictable.

(5) Access. A desirable drop zone has anadjacent road, or terrain adjoiningthe area, that offers good access forvehicles, so that the dropped suppliescan be recovered and transportedconveniently.

Section III. WATER SUPPLY

142. ImportanceAn adequate supply of water for drinking,

sanitation, construction, and vehicle operationis one of the fundamental needs. In arid andsemiarid regions, water supply affects plansand operations. Entire campaigns in desertlands may be conducted solely to secure water

sources or to deny them to an enemy. Allfeasible sources and methods for developingthem must be considered when making plansfor the water supply of troops and installa-tions. Development data are obtained from re-connaissance, map study, reports or runoff andrainfall average, and geological surveys. Water

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sources are located by a study of maps, aerial water than do those fed mainly by surfacephotographs, water resources data, and intelli-gence reports, then verified by field reconnais-sance if feasible. Detailed information con-cerning water supply is contained in TM 5-700.

143. Sourcesa. Basic Considerations.Water may be ob-

tained from wells, streams, springs, lakes, andmunicipal or other supplies that are alreadydeveloped. Water for permanent and semi-permanent installations also may be securedfrom the distillation of sea water or the drain-age from building roofs. Investigations to selecta water source must consider the quantity andquality of the water, and the conditions at theproposed sites from which the water supplywould be secured.

b. Quantity. The quantity of water availablein an area depends chiefly upon the climate. Intemperate and tropical regions with less than60 centimeters (25 inches) of annual precipi-tation, most streams become dry in droughtperiods. Streams usually flow throughout theyear in temperate regions with more than 60centimeters (25 inches) of annual rainfall andin tropical regions where the rainfall exceeds90 to 100 centimeters (35 to 40 inches). Sea-sonal variations may reduce the flow of waterbelow the required amount or result in waterpoints being flooded by seasonal high waterperiods. The seasonal characteristics of watersources should be obtained from local inhabi-tants. Terrain studies usually indicate alter-nate water sources for use in case the primarysources dry up, become flooded, or cannot beused because of enemy action.

c. Quality. Color, turbidity, odor, taste, min-eral content, and contamination determine thequality of water. TM 5-700 gives methodsfor estimating these characteristics and de-scribes the use of standard test kits. The qual-ity of water will vary according to the sourceand the season, the kind and amount of bac-teria present, and the presence of dissolvedmatter or sediment. Streams in inhabitedregions commonly are polluted, with the sedi-ment greatest during flood stages. Streams fedby lakes and springs, with a uniform flow, areusually clear and vary less in the quality of

runoff. Water in large lakes generally is ofexcellent quality, the purity increasing withthe distance from shore. Very shallow lakesand small ponds are usually polluted.

d. Site Requirements. The ease with whicha water source can be developed, operated, andmaintained is determined largely by the loca-tion and the routes of communication. Thedesign of the collecting system and the diffi-culties of development, operations, and main-tenance are partially influenced by site condi-tions, topography, soils and vegetation. Amilitary water point should be located as closeas possible to a main route without interferingwith traffic. An all-weather access road shouldlead to the place of storage, with a turnaroundor separate exit, and an all-weather off-roadparking area for trucks waiting to be filled. Inlocating the water point, attention is given toconcealment and cover, possible nearby targetswhich may attract enemy fire, drainage, roadconnections, condition of the banks and thebed if surface water is being drawn, and themeans required to develop the source. Exist-ing water supply systems are used when care-fully checked by engineers and medicalauthorities. Purification units may have to beinstalled. The possibility of contamination byenemy agents also must be considered.

144. Surface Watera. Regional Variations. Surface water

sources are generally more accessible and ade-quate in plains and plateaus than in moun-tains. Large amounts of good quality waternormally can be obtained in coastal, valley, oralluvial and glacial plains. Although largequantities also can be secured in delta plains,the water may be brackish or salty. Suppliesof water are scarce and difficult to obtain onlacustrine, loess, volcanic, and karst plains. Inthe plains of arid regions, water usually cannotbe obtained in the quantities required by amodern army. Much of the water that is avail-able is highly mineralized. In the plains andplateaus of humid tropical regions, surfacewater is abundant, but it is generally pollutedby bacteria and requires treatment. Perennialsurface water supplies are difficult to obtain inArctic regions. In summer, water is abundantbut often polluted. In winter it can be obtained

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from beneath the ice in the larger lakes and fans, glacial outwash plains, and alluvialstreams, but its quality is poor because of ahigh organic content.

b. Springs and Seeps. There are two types ofsprings or seeps: those originating at the baseof steep slopes where the topography breaksabruptly, and those caused by faulting. Thefirst type is found along the edges of a valley,and has a perennial flow and fresh, cold water.The second type is caused by the fracture ordisplacement of confining clay or rock layersabove an artesian water-bearing formation(aquifer), thus forcing the water in the ar-tesian zone to the surface. Springs of this typeoften are thermal, and may contain excessiveamounts of minerals. Frequently the depth ofa source of water can be estimated by thetemperature of the water; the hotter thewater, the deeper the source. Spring water isgenerally clear, cool, and low in organic im-purities, but may be hard because of a highdissolved mineral content. In regions where sea-sonal rainfall varies greatly, the spring flowoften decreases during long periods of dryweather. The heavy infiltration of surfacewater causes some springs to become turbid,and may produce contamination.

c. Streams. Streams are the most commonsource of surface water supply. Streamflowmay vary with precipitation, temperature, andthe amount of vegetation. Turbidity and min-eral content vary with the flow and withwatershed conditions. Since large flows pro-duce high dilution, many such streams may besuitable sources of water supply although theyreceive raw or partially treated sewage. How-ever, water from such streams must be settled,filtered, and chlorinated before use.

d. Lakes. Ordinarily, lakes are a satisfactorysource of water supply. The water level andaverage yield in small lakes may vary. Manylakes receive sewage flow, have a high contentof dissolved minerals, and may have consider-able vegetative growth or contain vegetable oranimal organisms. These can usually be re-moved by purification processes.

145. Ground Watera. Source. Ground water is obtained without

difficulty from unconsolidated or poorly con-solidated materials in alluvial valleys andplains, streams and coastal terraces, alluvial

basins in mountainous regions. Areas of sedi-mentary and permeable igneous rocks also mayhave fair to excellent aquifers, although theydo not usually provide as much ground wateras areas composed of unconsolidated materials.Aquifers of this type underlie coastal plains,inland sedimentary plains and basins, karstand volcanic plains and plateaus. Largeamounts of good-quality ground water may beobtained at shallow depths from the alluvialplains of valleys and coasts, and in somewhatgreater depths in their terraces. Large quan-tities may also be secured from shallow wellsin delta plains, although it is apt to be brackishor salty. Aquifers underlying the surface ofinland sedimentary plains and basins also pro-vide adequate amounts of water. Often theseformations lie with a few hundred feet ofthe surface. Those at greater depths yield veryhard water which may be too highly mineral-ized to be drinkable. Abundant quantities ofgood-quality water generally can be obtainedfrom shallow to deep wells in glacial plains. Inloess plains and plateaus, small amounts ofwater may be secured from shallow wells, butthese supplies are apt to fluctuate seasonally.Water from wells usually is clear and low inorganic impurity, but it may be high in dis-solved mineral content.

b. Plains. Large springs are the best sourcesof water in karst plains and plateaus. Wellsmay produce large amounts if they tap under-ground streams. To estimate the possible yieldof proposed wells, information is sought aboutexisting wells that tap similar water-bearingformations in the vicinity. The siting anddrilling of wells is difficult because the areas ofpermeability and the solution cavities in lime-stone cannot be easily predicted. Shallow wellsin low-lying lava plains normally produce largequantities of ground water. In lava uplands,where water is more difficult to find and wellsare harder to develop, careful prospecting isnecessary to obtain adequate supplies. In wellsnear the seacoast, excessive withdrawal offresh water may lower the water table, allow-ing infiltration of salt water which ruins thewell and the surrounding aquifer. Springs andwells near the base of volcanic cones may yieldfair quantities of water, but elsewhere in vol-canic cones the ground water is too far below

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the surface for drilling to be practicable. (2) Direct pumping. In direct pumpingc. Climate. Plains and plateaus in arid cli-

mates generally yield small, highly mineral-ized quantities of ground water. In semiaridclimates, following a severe drought, therefrequently is a flow of subsurface water underan apparently dry streambed that may yieldconsiderable amounts of excellent water.Ground water is abundant in the plains ofhumid tropical regions, but usually it is pol-luted by bacteria. In arctic and subarcticplains, wells and springs fed by ground waterabove the permafrost are dependable only insummer; some of the sources freeze in winter,and subterranean channels and outlets mayshift in location during the seasons. Wells thatpenetrate aquifers within or below the perma-frost, however, are good sources of perennialsupply.

d. Hills. Adequate supplies of ground waterare hard to obtain in hills and mountains com-posed of gneiss, granite, and granitelike rocks.They may contain springs and shallow wellsthat will yield water in small amounts.

e. Military Use. Both large- and small-diam-eter wells are used for military installations.Large-diameter wells usually are dug by hand,in diameters up to 15 meters (50 feet). Theymay be used as reservoirs, the water level fall-ing during periods of withdrawal and beingreplenished from subterranean flow duringperiods of light demand. Small-diameter wells,normally, made by driving, jetting, boring, ordrilling, do not provide storage. Deep wells aredrilled by percussion rigs or rotary equipment.The amount of water obtained from deep wellswill depend upon local conditions. They are lesssubject than shallow wells to seasonal fluctua-tion, contamination, and pollution. Informationabout wells and well-drilling is in TM 5-297.

146. Water Supply Systemsa. Types. There are 3 basic types of water

supply and distribution systems-(1) Gravity. The storage reservoirs of

gravity distribution systems usuallyare located high enough to developthe required pressure and flow. Some-times the storage tanks are filled bygravity from springs located at ahigher level, but ordinarily they arefilled by pumps.

systems, ordinarily there are no ele-vated storage tanks. The water ispumped into the distribution systemfrom ground storage reservoirs orwells at a rate depending on demand.

(3) Combination. Primary mains are sup-plied by both gravity and directpumping in combination systems.

b. Parts. The essential parts of a water sup-ply system are-

(1) Headworks, usually a reservoirformed by a dam.

(2) Conduit, sometimes an open canal oran aqueduct, but more commonlymade of wood, iron, or steel that iswatertight to prevent contaminationand losses by evaporation, absorp-tion, and changes in temperature.

(3) Distributing system, which connectswith the plumbing in buildings. Largemains carry the water from thesource to service pipes, which take itto individual buildings and other out-lets.

147. Information Requirements - WaterSupply

Special water supply studies are made by en-gineers, assisted by geologists and hydrologists.The information required in terrain intelli-gence studies includes the following-

a. General.(1) Normal level of water table and vari-

ations.(2) Yield of springs and wells, and vari-

ations.(3) Potability and contaminations.(4) Underground flow in dry water-

courses.b. Surface Supplies.

(1) Total drainage area.(2) Rainfall and runoff data.(3) 'Sources and kinds of possible con-

tamination, including sewage or in-dustrial wastes.

(4) Chemical and bacteriological analy-ses.

c. Wells.(1) Rainfall data.(2) Reports of available well logs and

test data.

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(3) Physical, chemical, and bacteriolog-ical analyses.

d. Existing Water Supply System.(1) Source of supply.(2) Quantity provided; ultimate capacity.

(3) Treatment methods.(4) Distance from supply to proposed

military user point.(5) Pressures.(6) Chemical and bacteriological analy-

ses.

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CHAPTER 8

TERRAIN STUDIES

Section I. BASIC FEATURES

148. Descriptiona. Preparation. A terrain study is an intelli-

gence product which presents an analysis andinterpretation of the natural and manmadecharacteristics of an area and their effects onmilitary operations. It is a compilation of onlythat information which has a direct bearingon some existing requirement. This study isprepared at all echelons to provide the intelli-gence officer with an analysis of the terrainfor use in preparing the analysis of area ofoperations that forms part of his overall intelli-gence estimate for the commander, and for useby other staff elements for planning and con-duct of operations. The preparation of ananalysis of area of operations is discussed inFM 30-5. Above army level, terrain studiesare prepared primarily, to assist the com-mander and his staff. At lower levels, terrainstudies are intended chiefly for use in tacticaloperations and include more details of the ter-rain and its effects.

b. Topics. Special studies devoted exclusive-ly to certain terrain features or effects may beprepared to meet the requirements of a parti-cular plan or operation. These are produced bytechnical personnel or teams, and include, butare not limited to, studies concerning-

(1) Construction problems.(2) Movement.(3) State of ground.(4) Water resources.(5) Lines of communication.(6) Site selection.(7) Coast and landing beaches.(8) Inundation.(9) Urban areas.

(10) Barriers.(11) Defenses.

(12)(13)(14)(15)(16)(17)(18)(19)

Airborne landing areas.Soils.Rock types.Drainage.Climate.Surface configuration.Inland waterways.Other military aspects.

149. Prerequisite InformationBefore initiating the study, one must know

the area to be covered, the mission and typeof operation, the specific information required,and the time period to be considered. Terrainintelligence is produced continuously at allechelons. The preparing unit maintains a fileof intelligence data, drawing upon it for per-tinent matter when he is directed to make aterrain study. Additional information is ob-tained from the sources and agencies discussedin chapter 3.

150. Formata. Content. A specific terrain study will not

cover every item in outline, but only thoseitems applicable to the operation being planned.Used in this manner, the terrain study forminsures uniformity of presentation yet permitsthe flexibility imposed by terrain analysis.

b. Primary Requirement. The primary re-quirement for a terrain study at army, corps,or division level is that it must present theintelligence in a form that can be easily uti-lized by field units. The study must be concise,presenting only pertinent information. Writtendescription should be kept to a minimum. In-telligence should be presented graphicallywhenever possible.

c. Automation. The intelligence portion of

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the Tactical Operations System (TOS) auto- (printed in gray monochrome) or is an overlaymatic data systems within the Army in thefield (ADSAF-75) is an information process-ing system which uses automatic data process-ing equipment as a tool for battlefield com-manders to help them exercise command andcontrol of their forces and make effective andtimely decisions. The computer center acceptsinformation from various sources, includingthat from forward observers as well as fromother computer centers. This information isautomatically assembled, sorted, evaluated, andstored by the computer. This computer drivesan automatic, constantly up-dated map displaywhich provides the commander with a view ofhis entire operation. The map includes symbolsrepresenting the size, type, and location of allforces, both friendly and enemy, as well asthe terrain features, supply dumps, and otherintelligence information necessary for the ef-fective evaluation and direction of the opera-tion. This computer center consists of a centralprocessor, memory units, and auxiliary equip-ment. It also has an automatic communicationsswitching capability which permits contactwith all units having an organic intelligencesection and a primary intelligence collectionmission. In addition, it has operating andmonitoring controls for the system.

151. Compilationa. Format. The format suggested for the

terrain study consists of three parts: text, aterrain study map, and a regional descriptionsection. A fourth major paragraph, "Analysisof Area of Operations," is prepared by theintelligence officer. The scope of this paragraphis described in FM 30-5. The text follows thesequence of the sample terrain study (app. C).It presents the terrain intelligence called forin the applicable section of the form Tablesand charts are used to simplify, amplify, andclarify the presentation. The text should be asconcise as possible.

b. Map. Wherever possible, terrain intelli-gence should be presented on a terrain studymap, based on a topographic map of appropri-ate scale. A map scale of 1:50,000 is usuallyutilized for brigades and divisions. Corps andarmy headquarters usually do not require ascale larger than 1:250,000. The terrain intelli-gence is overprinted on the topographic map

to the map. Appropriate symbols are used topresent items of terrain intelligence. Con-ditions for movement are portrayed by des-ignated movement colors.

c. Regions. Terrain features exist in certainpatterns or combinations, which create distinc-tive terrain regions. Usually the area of studyencompasses several terrain regions. The re-gional description section of the terrain studygives the user an understanding of the terrainby explaining the combined effect of the ter-rain features in the regions. This section con-sists of a sketch map delineating the terrainregions and of brief descriptions summarizingthe terrain intelligence for each region.It may be printed on the back of the terrainstudy map. The information presented in theregional description section enables the userto evaluate the factors influencing movementand to interpret changes in movement whichmight be caused by changes in weather.

152. ReproductionReproduction of terrain studies should be

done by the fastest, cheapest, and easiestmethod. Only as many as necessary for pri-mary users should be made. The engineertopographic battalion assigned to army has thecapabilities for map reproduction. The battal-ion can draft and reproduce in bulk the terrainstudy map mentioned in paragraph 151. It canalso perform the other printing and draftingnecessary for the reproduction of terrainstudies. The engineer topographic company as-signed to corps has basically the same capabili-ties as the topographic battalion in the typeof work it can do, but is limited in volumeand equipment. A division has no organictopographic units. Terrain studies are producedby means of duplicators which can produce amap-size paper. The type and quality of terrainstudies are limited only by the degree of skilland imagination on the part of the personnelwho are responsible for this function.

153. DisseminationThe Engineer or Engineer Terrain Detach-

ment, or G2 Staff Engineer Officer, dissemi-nates the completed terrain study to the G2and other interested staff elements. The G2utilizes the terrain study according to the tac-

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tical situation and presents the resulting ter- in planning and preparing their own terrainrain estimate to the commander. If necessary,the terrain study is disseminated to subordi-nate and adjacent units. The terrain study isalso disseminated through engineer channels.Copies are sent to lower echelons to assist them

studies. A copy is sent to higher engineerheadquarters, and another is sent throughenginner channels to the Office of the Chief ofEngineers.

Section II. TERRAIN AND CLIMATE

154. Basic Factors Affecting TerrainThe basic factors for a terrain analysis are

discussed under item 2 of the terrain study(app C). The factors discussed are climate,topography, and when applicable, coastal hy-drography. Although climate and ocean-ographic aspects of coastal hydrography arenot elements of terrain, they have a direct in-fluence on the usefulness of an area for mili-tary activities. Appendix C compiles the ter-rain intelligence that is pertinent to the areaof the planned operation. The extent of thearea will vary with the echelon performingthe compilation. Terrain studies at higherechelons may present fairly extensive descrip-tions for planning purposes, but terrain studiesat lower echelons, having a more definite di-rection and limit as to area, time, and purpose,restrict their descriptions to the intelligenceapplicable to the operation planned.

155. Climatea. Elements. The elements of the climate

discussed in a terrain study include visibility,temperature, precipitation, humidity, winds,clouds, and electrical disturbances. Not allmust be discussed in every terrain study, be-cause the factors selected depend on the area,time, and type of operation planned. The areaof operations influences the description of theclimate. The climate of a large area may bedescribed in general terms, whereas a descrip-tion of a small area will be quite specific. Theimportance of certain elements of climate de-pends upon the area. The time that an opera-tion commences determines the type of intelli-gence presented. Climatic data must be usedif the starting date is more than a week ortwo in the future. (Weather forecasts will beused in the terrain estimate for 5 days or less.)The type of operations planned determines thepertinent elements of climatic information to

be furnished. Planning of airborne operations,amphibious operations, and other special op-erations requires knowledge of weather ele-ments not usually required in normal groundoperations. These considerations are discussedin greater detail in manuals pertaining to air-borne and amphibious operations.

b. Factors. The methods of describing vari-ous factors of climate are discussed below.

(1) Visibility. Certain fixed data are bestpresented graphically. Times of sun-rise, sunset, moonrise, moonset,BMNT, EENT, and phases of themoon are best presented on a chartto indicate periods of degree of visi-bility. Such a chart is included in thesample terrain study. Where perti-nent, tide movements can also be pre-sented on this chart. Other deterringinfluences on visibility, such as fog,smoke, dust, or snowstorms, are dis-cussed in the text.

(2) Temperature. This information isgenerally presented in tabular form.Temperature predictions based solelyon climatic studies cannot forecastthe expected temperatures, but candescribe the range of temperaturesthat can be expected in a particularlocation by either of two methods. Bythe first method, the mean tempera-ture, the mean maximum and meanminimum, and the absolute maximumand absolute minimum temperatureswhich can be expected for the periodcan be indicated. The mean tempera-ture alone has little significance sinceit gives no indication of the range ofthe temperature variation. The sec-ond method is to tabulate the numberof days of the period that the tem-perature can be expected to exceed or

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fall below stated temperatures. Tem-perature effects on other terrain fea-tures should be described adequatelywhen significant, such as effect on soiltrafficability and freezing or thawingof water bodies.

(3) Precipitation. This information,based on climatic studies, can statethe type and amount of precipitationencountered during a particular pe-riod; the number of days within thatperiod on which certain amounts ofprecipitation can be expected; and thevariability of precipitation from yearto year. A statement of the totalamount of precipitation that can beexpected over a period of time haslittle significance in itself, since a 3-inch rainfall means one thing whenspread over 30 days and a totallydifferent thing when concentrated in1 day during the 30-day period. Theeffect of precipitation on other ter-rain features, particularly waterbodies and the trafficability of soils,should be described.

(4) Winds. Wind data based on climaticresearch present the direction, inten-sities, and duration that can be ex-pected over a period of time. Thesefacts are best expressed graphicallyby means of a wind rose or may bereferenced to the Weather Map Scaleof Wind Velocity. Wind rose data maybe secured from AWS when specifi-cally required by a commander. Theeffect of wind on surface materialsand on waves is described when per-tinent.

(5) Humidity. Exact descriptions of hu-midity are not usually necessary, butthe effects of humidity on operationsis described when significant. The de-scription should consider fog con-ditions and the effect of humidity inreducing the efficiency of personnelor in creating problems of storageand maintenance of supplies andequipment.

(6) Clouds. Data based on climatic re-cords signify the approximate number

of days during a specific period thata certain degree of cloud cover canbe expected. There is also a statementas to what time of the day or nightcertain cloud coverage can be ex-pected. Related conditions such asstorms and fog are also describedwhen applicable.

(7) Electrical disturbances. This subjectis discussed only when it has an im-portant effect on proposed operations.The type of disturbance, its periodof occurrence and duration, and itseffect on planned operations are de-scribed in the text when pertinent.

156. Natural and Manmade Featuresa. Relief. Relief is described in the text and

symbolized on the map to highlight significantrelief features, but not to repeat the detail ofa topographic map. The general picture of therelief of an area may be indicated by ridgeand stream lining, which accentuates the ma-jor ridges and drainage patterns. This consistsof emphasizing the streams by drawing overthem with a blue pencil and emphasizingridges with brown pencil. Ridge lining orstream lining can be used separately, if de-sired, but the combination of the two is moreeffective. Ridge and stream lining emphasizesthe compartmentation of an area, but does notshow relative elevations or slope (fig. 57).Another method is to emphasize the principalcontours of an area. This is done by tracingover certain critical contour lines with a heavyblack pencil or by using different colored pen-cils to indicate different elevations. Thismethod has the advantage of not obscuringdetails on the map (fig. 58). Sharp slopes, suchas embankments, steep riverbanks, and cliffsare indicated by a red movement symbol whentraverse appears to be impracticable. In cer-tain cases, an area may be cut by numerousdraws and gullies which are significant butare not shown on topographic maps becausetheir depths are less than the contour interval.These draws and gullies are symbolized on themap. The effect on movement is discussedunder "movement" and illustrated graphicallyby movement symbols.

b. Drainage and Hydrography. Since drain-

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Figure 57. Ridge and stream lining.

age features are subject to change at leastseasonally, it is important that the terrainstudy describe the present condition of thedrainage features. The degree of detail in thedescription is usually determined by the eche-lon at which the study is prepared and theprimary purpose of the study itself. A higherechelon indicates only the major features onthe terrain study map, but lower echelon studycovering a smaller area can indicate the minordrainage features and give detailed descrip-tions of them.

c. Vegetation. Forests are indicated graphi-cally. The type of trees, deciduous and ever-green, the density of the forest, and the rangeof trunk diameters are noted on the map. Thetext describes other significant vegetation inthe area and the effect of weather on the vege-tation. Vegetation may be discussed under con-cealment, fields of fire, obstacles, and any otherpertinent aspects of the terrain.

d. Surface Materials. Higher echelon terrain

studies usually include a soils map. At armyand lower headquarters, this will not usuallybe feasible. A description of the types of sur-face materials is included in the surface ma-terial section of the study. The effect of surfacematerials on cross-country movement is an im-portant factor of the terrain study and is de-scribed graphically in that section. Surface ma-terials are also discussed in the sections onconstruction sites and construction materials.

e. Manmade Features. The terrain study de-scribes those manmade terrain features whichhave particular significance or which requiremore detailed description to be of value. Themore common manmade features are discussedbelow.

(1) The road-bridge-bypass system is de-scribed because of its influence onvehicular movement. A higher echelonstudy may describe graphically onlythe primary roads whereas a divisionstudy usually describes the secondary

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Figure 58. Contour emphasis.

and tertiary systems as well. Impor-tant bridges and bypass sites are in-dicated. (See DIA, AP-1-335-3-1-65-ADMIN and DIAM 57-5 for routeclassification symbols.)

(2) Airfields of all types are described.Their locations are shown on themap by standard topographic symbolsand an indication is given as to theirsize and condition. Further details

are given in a table.(3) Principal cities and towns are indi-

cated on the terrain study map, andare listed further in a table.

(4) Railroads are shown on the terrainstudy map, with detailed informationin a table.

(5) Hydrologic structures of all types aredescribed, with detailed informationin a table.

Section III. MILITARY ASPECTS

157. OperationsDetermining the military aspects of the ter-

rain for an operation requires a knowledgeof the terrain and of the operation planned.

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Not having complete knowledge of any specific ive shells are examples of such features.) Themilitary operation, the person preparing theterrain study should describe the military as-pects in terms of generalized operations. Theintelligence officer using the study will inter-pret them in terms of the operation beingplanned. This is particularly true of key ter-rain features and avenues of approach. De-scriptions of the aspects of terrain vary withthe echelon. At army level, descriptions aregeneral; at division level they are more de-tailed and specific.

158. Key Terrain FeaturesThe determination of key terrain features

requires a knowledge of the terrain, the ob-jective, and the plan of operations. As a rulethe person making this study may not have acomplete knowledge of the plan of operations,and therefore, he must determine those fea-tures that have a controlling effect on the sur-rounding terrain and list them as probable keyterrain features for consideration by the user.The description of these features includes adiscussion of their significance.

159. Observation and Fields of Firea. Observation. The description of observa-

tion includes an evaluation of the ground andair observation in the area, and a brief dis-cussion of the terrain features in that area thataffect observation. Periods of visibility are de-scribed by a visibility chart in the weather andclimate section. The effect of the terrain onobservation by special devices such as radar,infared equipment, and sound-ranging devicesis described when applicable. The descriptionof observation is generally included in thetext. A lower echelon study map may indicatethe location of individual observation points.

b. Fields of Fire. The description of fieldsof fire in the terrain study is included in thetext, and is primarily concerned with flat-trajectory fire. The description includes ageneral evaluation and a discussion of the ter-rain features that affect fields of fire. Featureswhich limit or restrict fields of fire are de-scribed in detail. Terrain features that createspecial problems in the use of high-trajectoryweapons are described when they exist. (Areasof marsh or volcanic ash that smother explos-

possible effect of terrain on nuclear actions isdescribed when pertinent.

160. Cover and ConcealmentThis includes a discussion of the problem of

constructing installations to provide cover,such as foxholes, bunkers, and undergroundinstallations. The means available for provid-ing cover from nuclear action is discussedwhen applicable. Concealment is described inthe text with reference to pertinent terrainfeatures such as forests which are portrayedgraphically. The amount of concealment andto what extent various type units can utilizeit are discussed.

161. ObstaclesThe description of obstacles includes a de-

scription of the general hindering character-istics of the terrain and a description ofspecific obstacles. The explanation of the gen-eral obstructive elements of the terrain is anoverall description and includes terrain fea-tures which are unimportant singly, but whichconstitute obstacles cumulatively, such as sys-tems of irrigation or drainage ditches, ter-races, and hedgerows. These are described inthe text and indicated graphically by move-ment symbols. Specific obstacles, such as riversor escarpments, are described individually.Obstacles that are known to be impracticablefor crossing by personnel or equipment areoutlined by red hachuring.

162. Avenues of ApproachThe determination of avenues of approach

involves a summation of all other military as-pects as they affect the mission of a particularforce. Fixing the avenue of approach involvesa tactical decision which is beyond the scopeof the engineer intelligence officer. His role inthe preparation of a terrain study is to presentinformation on the available avenues of ap-proach for consideration by the G2 and thecommander. This information is included inthe text. It includes a description of theavenues of approach and a brief discussion oftheir advantages and disadvantages.

163. MovementThe description of cross-country movement

138


conditions is the most important and detailed the availability of materials for constructionof the descriptions of military aspects of theterrain. The description of movement in thetext is devoted to a general evaluation of con-ditions for movement in the area and a dis-cussion of the terrain features and weatherconditions which affect movement. Movementis shown graphically on the terrain study mapby color symbols which represent an evalua-tion of movement conditions. The effect of allterrain features is considered in the text onmovement evaluation. The specific meaning ofsymbols as applied to the area of study is ex-plained in the margin of appropriate classifi-cation symbols. A more complete discussion ofareas of poor or doubtful movement than ispossible on the terrain study map is containedin the regional description section, to enablethe commander to determine conditions underwhich movement is possible through the area.

164. Construction MaterialsThe description of construction materials

presents information on the availability of con-struction materials in the area of operations.It includes data on the presence of developedand undeveloped sources of rock, sand, gravel,and aggregate, and of stocks of lumber, steel,and other construction materials. It is not adetailed report, but presents general data on

in the area. Availability of building materialsis discussed generally under military aspectsof the terrain. Detailed reports on the sourcesof construction materials are prepared separa-ately as required by engineer units.

165. Suitability of Sites for ConstructionThe description of construction sites includes

a discussion of sites for roads, airfields, andother surface and underground installations.This description should be suited to the needsof the echelon for which the study is prepared.The description does not indicate specific sites,but describes the general suitability of the areafor various types of construction. Building sitesare discussed generally in the text. Detailedreports on appropriate sites for specific con-struction projects are prepared separately asrequired.

166. Water SupplyThe description of water supply enumerates

the sources of water available in the area andevaluates their suitability for use by the troops.It includes a discussion of natural watersources and water supply systems. When per-tinent, the water requirements of the civilianpopulation are discussed. Water supply is dis-cussed in the text.

Section IV. COASTAL HYDROGRAPHY

167. Describing Coastal Hydrographya. Presentation. Descriptions of coastal hy-

drography are of interest primarily for am-phibious operations. They differ from overlandoperations only in the method of transporta-tion and types of routes by which they arriveat the area of operations. The terrain studyfor an amphibious operation includes: text,terrain study map, and tables. These are thesame elements which are in the land-operationstudy, but the terrain study for an amphibiousoperation must also include a means for pre-senting detailed intelligence about the landingarea. This is done by extending the three ele-ments of presentation mentioned above to in-clude descriptions of the landing area, andby use of a fourth element, the beach profilediagram. Application of this method of de-

scription to coastal hydrography is discussedbelow.

b. Text. The text describes the features ofcoastal hydrography, such as sea approaches,beach area, sea and surf, and tides. The de-scription is coordinated with the graphicpresentation. The effect of other terrain fea-tures on coastal hydrographic conditions isalso described, and includes the effect of in-land surface materials on beach composition.

e. Terrain Study Map. The terrain studymap shows potential amphibious landing areas.Since the terrain study map may be of toosmall a scale to be of value as a descriptionof the landing area, it is generally used to de-pict the configuration of the coast line, locationand length of the beaches, and location of exitsfrom the beaches.

139


a

iI4

0

0a~

Ut

140


d. Description. A description of both the hy- map describes the general configuration of thedrographic and terrain conditions for eachlanding area is included in a table.

e. Beach Profile Diagram. The beach profilediagram (fig. 59) is a large scale sketch ofthe offshore and nearshore area, the shore, andthe coastal terrain (hinterland). The waterlevels at high tide and low tide are shown inthe offshore, nearshore, and foreshore areas.In addition, the beach widths at high waterlevel and low water level and some of thecoastal terrain are shown. A profile of the areato the rear of the beach, showing landmarksvisible from the sea, is included if deemednecessary as a navigation aid for landing craft.Other data may be included if it is pertinentto the operation.

168. Sea Approachesa. Offshore Approaches. The offshore ap-

proaches are usually of interest only to navalforces and therefore are not described in theterrain study. When description is necessary,a hydrographic chart may be utilized.

b. Nearshore Approaches. The nearshore ap-proaches are of primary interest to landingforces and, as such, require a detailed descrip-tion. The description should present a generalevaluation of the nearshore area, and describebottom conditions and the effect of sea, swell,breakers, surf, tides and currents. Also de-scribed are any special phenomena such as seavegetation thick enough to be classed as anobstacle, ice conditions, unusual or tricky cur-rents. The landing area map presents a graphicdescription of the nearshore area. The generalrelief of the area is described by contours basedon the hydrographic chart datum plane. Ob-stacles are located on the map and any specialfeatures are identified by special symbols.Representative profiles, as necessary, describethe gradient of the nearshore area.

c. Beaches and Beach Exits. The text pre-sents a general description of the beach area,covering such items as the capacity of thebeach, its composition and trafficability, andthe capacity of beach exits. The terrain study

coast, the location and length of the beaches,and the beach exits. The regional descriptiondeals with the beaches as part of topographicregions. The landing-area map presents a de-tailed graphic description of the beaches. Itportrays the dimensions of the beaches and thelocation of obstacles areas, and describes thebeach exits. The colors used in the landing-areamap conform to the color key used in all move-ment maps. The water tint usually extends tothe high water shoreline, or at time to mean sealevel, depending upon the mapping agency.One or more profiles are used to describe thebeach gradient. If necessary, the area to therear of the beach is included to indicate theposition of landmarks as seen from seaward.

d. Sea and Swell. Sea is defined as wavescaused by local winds, whereas swell refers towind-generated waves that have advanced be-yond the region of generation. The directionof sea is that of the local wind, whereas thedirection of swell is independent of, but maycoincide with the local wind. Both sea andswell may be present at the same time. Seaand swell must be described in the text, withroses that show the frequency of various heightcategories by direction.

e. Breakers and Surf. Surf is the disturbedwater area extending from the outer breakerline to the limit of uprush on the beach.Breakers are waves that shoal over a reef oron a shore. Hazards to landing increase withincreasing breaker height, and vary withperiod of waves, type of breakers, and thedirection of breaker approach onto the beach.Breakers and surf are described by the text,and breaker roses show frequency by directionof specified breaker height ranges.

f. Tides. Tide information is presentedgraphically. Curves portray times of high andlow tides, and can be incorporated into thevisibility chart. A chart showing the tides dur-ing the period of the study is included in themargin of the landing-area map for predictingthe heights of the water at any given time.Special tidal conditions and tidal currents aredescribed in the study text.

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CHAPTER 9

TRAFFICABILITY

169. Estimating Soils TrafficabilityThe purpose of this chapter is to assist in-

telligence and reconnaissance personnel todetermine the trafficability of soils to supportcross-country movement of military vehicles.Increased emphasis on the military concept ofdispersion, which requires cross-country move-ment has increased the requirement for infor-mation on soil trafficability. Most informationon trafficability pertains to military vehiclesoperating on various unfrozen soils in thetemperate zones. The procedures for measure-ment of soil trafficability can also be appliedto unfrozen soils that have been subjected tofreeze-thaw cycles. An estimate of trafficabilitycan be made with the aid of this chapter ifsomething is known of the general weatherconditions, the topography and the soils ofthe area.

170. Weather and ClimateInformation about the weather and climate

is available from meteorological records, andclimatology textbooks, and by interrogation ofprisoners. Only two general conditions ofweather apply to trafficability estimates, thedry period and the wet period.

a. Traficability During Dry Period. Duringa dry period all soils usually are passable unlessthe area is low-lying and poorly drained or iskept wet by underground springs. Sand in adry state is less trafficable than in a wettercondition (with the exception of quicksand).

b. Trafficability During Wet Period. Whenmoisture is added to a soil its strength ischanged. Different soils are affected different-ly by moisture. During a wet period, all soilswith the exception of clean sands and gravelsprovide poor trafficability. The relative traf-ficability ratings of soil types under set con-

ditions are given in figure 60. This figure isexplained in paragraph 178.

171. TopographyThe effects of slopes on soil requirements

for vehicle performance can be shown inquantitative units when actual measurementsof the cone index (para 174d) can be made,but in estimates of trafficability only generalstatements concerning slopes are feasible.Slopes require better soil traction conditionsfor vehicle movement than does level terrainof a similar soil type. Other factors pertainingto trafficability that must be kept in mind arethat ridges are generally more trafficable thanthe adjacent valley, that downhill travel iseasier than uphill travel, and that low tirepressure increases traction. During the dryseason, sand slopes of approximately 30 per-cent are impassable. Fine-grained soils andsands with fines which are poorly drained maybe trafficable up to a 45 percent slope. Duringthe wet season a 30 percent slope is the maxi-mum that should be tried on any type soil.

172. Soils MapsTwo types of soils maps exist. One type

classifies the soils according to the Unified SoilClassification System (USCS), as used indetermining trafficability. The second type ofsoils map employs the agricultural system ofsoil classification (ASSC). This type is notused by the military. It is mentioned here toavoid confusing it with the USCS. Soils areformed by the action of the following factors:parent material, climate, age, chemical action,topography, and vegetation. A trained analystcan estimate the soil types by using a geologicmap, providing he has a general knowledge ofthe climate, the topography, and the vegeta-tion of the area.

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173. Aerial PhotographsThe full utilization of aerial photos in esti-

mating trafficability is presently being studied.At present the following information pertain-ing to trafficability is obtained from aerialphotographs.

a. Topography. Aerial photographs are agood source of topographic information. Esti-mates of elevations and slopes can be madefrom stereopairs by properly instructed per-sonnel. Accurate elevations and slopes canbe obtained by trained operators using me-chanical equipment such as Multiplex andKelch plotters.

b. Soils and Moisture Conditions. In thepresent stage of development, the techniquesfor identifying soils from airphotos are socomplex that only well-trained technicians canemploy them to their fullest extent. However,certain general facts may be used to advantageby personnel with a minimum of training. Forinstance, orchards usually are planted in well-drained, sandy soils; vertical cuts are an evi-dence of deep loessial (silty) soils; tile drainsin agricultural areas indicate the presence ofpoorly drained soils, probably silts and clays.On a given photo, light color tones generallysignify higher elevations, sandier soils, andlower moisture contents than do dark colortones. The same color tone does not alwaysindicate the same soil conditions even on thesame photo. Color tone may have entirely dif-ferent significance on two separate photos.Also, natural tones are apt to be obscured andmodified by tones created by vegetation (na-tural and cultivated), plowed fields, and shad-ows of clouds.

c. Vegetation. Dense grass, especially if wet,will cause slipperiness. Tall grass will oftenrestrict visibility. Heavier vegetation such asbrush and trees will decrease trafficability ifthe vehicles must push aside this vegetationas they advance. The presence of vegetationin sands usually stabilizes the soil, thus increas-ing its trafficability. Decaying vegetation in-cluding the roots, found especially in thenorthern latitudes, adds to the support of thesoil if the soil is weak. The limited testing thathas been done shows that if the mat of partial-ly decayed vegetation is 6 or more inches thick

it will support 40 to 50 passes of very lightvehicles such as the M29 amphibious cargocarrier. Heavier vehicles will break throughafter 2 or 3 passes.

d. Obstacles. A complete assessment of thetrafficability of a given area must include anevaluation of obstacles such as forests, rivers,boulders, ditches, hedgerows, steep slopes andcliffs, and embankments. Aerial photographsare valuable in identifying these features.

174. Trafficability Termsa. Trafficability. The capacity of a soil to

withstand traffic of military vehicles.

b. Bearing Capacity. The ability of a soilto support a vehicle without excessive settle-ment of the vehicle. California Bearing Ratiois used in denoting design values.

c. Traction Capacity. Ability of a soil toresist the vehicle tread thrust required forsteering and propulsion.

d. Cone Index. A numerical indication ofthe carrying ability (resistance to penetrationby wheels and tracks of vehicles) of a soil.An index of the shearing resistance of soilobtained with the cone penetrometer; a di-mensionless number representing resistanceto penetration into the soil of a 300 cone witha 1/2-sq in. base area (actually load in poundson cone base area in square inches). TM 5-530discusses this in detail.

e. Remolding. The changing or working ofa soil by traffic, or by a remolding test. Re-molding may have a beneficial, neutral, or det-rimental effect on soil strength.

f. Remolding Index. The ratio of remoldedsoil strength to original strength, determinedin accordance with procedures described inTM 5-530.

g. Rating Cone Index. The measured coneindex multiplied by the remolding index; itexpresses the soil-strength rating of an area.

h. Critical Layer. The soil layer in which therating cone index is considered a significantmeasure of trafficability, or the layer of soilwhich is regarded as being most pertinent toestablishing relationship between soil strengthand vehicle performance. Its depth varies withthe weight and type of vehicle and the soil

143


profile, but it is normally the layer lying 6 or 1. Mobility Indez. A dimensionless number12 inches below the surface.

i. Vehicle Cone Index. The index assignedto a given vehicle that indicates the minimumsoil strength in terms of rating cone indexrequired to permit 50 passes of the vehicle.

j. Stickiness. The ability of a soil to adhereto vehicles, wheels, and tracks.

k. Slipperiness. Low traction capacity of asoil's surface due to its lubrication by wateror mud.

which results from a consideration of certainvehicle characteristics.

m. Maximum Tractive Effort. The maxi-mum continuous towing force or pull a vehiclecan exert expressed as a ratio or percentageof its own weight.

n. Fine-Grained Soil. A soil of which morethan 50 percent of the grains, by weight, willpass a No. 200 sieve (Unified Soils Classifica-tion System (USCS)).

Soil Rffect ofTypo Slipr- Stick.Sbo Lo.e Ias.

Vebicle CaeorIl 1 2 I i gI 5 1 6 1 7

Vehle. Cone IdLO 60 bO IT a, .1io L' F rI I I 7 II F I m

SHgh T.eay, Wvetaeton. Condtion

SPSM son.GM NomeSM NonC1 SlightCC Slightsc Sliaht

M Slight

SlightIca Slight

Sc Moderate

SM-Sc Slight8 BSevre

GM SlightSM slightCL Moderate-L ModerateCL M oderatOL ModerateC ModeratePn Mdrate

GV GP

GC

SMS

COL

SPc

M

C,aM

OLcRPt

one

SevereSevereSevere

SevereSvereSlightSlightSlightSevereSevere

SreSevere

None

NoneNone

oneModerateSlightSlightSlightSlightsll~tNoneNoneNone

None

NlioneSevere

oderat

NoneModerate

Slihbt

Slgh

McG.^t

on.

slereModerate

silsbt

Moderate

SevereModersteNoneSlight

Slight

SlightSliht

Slight

PROBaBITYS OF VIEiCL. "O" O LET VEL

xoeLlent Goreater ta g C Go r eliability, bse.d o

G Cd 76 to 9% = aIr reibility, bed on

ir 50gW to 5%

P roor Lo.. tan 50%

ot: Velhicle cater coe inx rae a.n given r . tL U.

. Ale.. only to d ehicles without traction det.ces.

Figure 60. Soil tra.ficability classification (USCS).

anazlyis of dat

jieinnt

144


o. Coarse-Grained Soil. A soil of which 50 60 for those desiring this technical informa-percent or more of the grains, by weight, willbe retained on a No. 200 sieve.

p. Sand with Fines, Poorly Drained. A sandin which water content greatly influences thetrafficability characteristics. These soils reactto traffic in a manner similar to fine-grainedsoils. They usually contain 7 percent or moreof material passing the No. 200 sieve, andlittle or no gravel.

175. Soil Trafficability Tablea. Soil Type Symbols. The soil type symbols

used on figure 60 are those employed in theUnified Soil Classification System (USCS).The symbols are given on the extreme left ofthe figure and also in the graphic portion. Theduplication aids in the reading of the graphs.These letter symbols are explained in table 2.Hyphenated letters indicate a mixture of typesof soils.

Table 2. Soils SymbolsSnmbol.GW -__--_-___ gravel-sand mixtures, little or no

fines.GP ____________gravel-sand mixtures, little or no

fines.SW __._____ . .gravelly sands, little or no fines.SP ___-g____- - gravelly sands, little or no fines.CH ___---______inorganic clays of high plasticity, fat

clays.GC ._.--______-gravel-sand-clay mixtures.SC ____________sand-clay mixtures.

CL _.- . .._____.gravelly clays, sandy clays, inorganicclays of low to medium plasticity,lean clays, and silty clays.

GM __. ..______gravel-sand-silt mixtures,

SM ____________sand-silt mixtures.ML __-______--low plasticity silts.MH _....i..__-inorganic silts, micaceous or diato-

maceous fine sandy or silty soilsand elastic silts.

OL --- _. ._. ... organic silts and organic silty claysof low plasticity.

OH ___-_-____-organic clays of medium to high plas-ticity and organic silts.

Peat, muck, and swamp soils are not classified in theabove list because such soils are almost always im-passible except for light amphibious-type vehicles.

b. Strength Measurements. The probableranges of the cone index (CI), the remoldingindex (RI), the rating cone index (RCI), andthe mean rating cone index are given on figure

tion. For most trafficability purposes this in-formation may be folded out of view tosimplify the reading of the remainder of thetrafficability chart. Information on thestrength measurements is given in TM 5-530.

176. Slipperiness and StickinessThe information on figure 60 pertaining to

stickiness and slipperiness is self-explanatory.The following is general information on eachof these two factors.

a. Stickiness. No instrument for measuringthe effects of stickiness on the performanceof vehicles has been devised. Stickiness willoccur in all fine-grained soils when they arecomparatively wet. The greater the plasticityof soil, the more severe are the effects of sticki-ness. In general, stickiness will have adverseeffect on the speed and faclity of travel andsteering of all vehicles. It will immobilizesmall tracked vehicles like the M29 weasel,but will not stop the larger and more power-ful military vehicles. Removal of fenders willreduce stickiness effects on some vehicles.

b. Slipperiness. Like stickiness, the effectsof slipperiness cannot be measured quantita-tively. Soils which are covered with water ora layer of soft plastic soil usually are slipperyand often cause steering difficulty, especiallyto rubber-tired vehicles. They can often im-mobilize vehicles, especially when slipperinessis associated with low bearing capacity. Slip-periness effects assume greater significance onslopes. Sometimes slopes whose soil strengthis adequate may not be passable because ofslipperiness. The use of chains on rubber-tiredvehicles usually will be of benefit in slipperyconditions.

177. Vehicle CategoriesMilitary vehicles are divided into s e v e n

categories according to a cone i n d e x rangeas shown in table 3. These vehicle categories,1 through 7, are shown at the top of figure60.

a. Vehicle Cone Index. This index is showndirectly below the vehicle category range onfigure 60. It is helpful in showing the traffica-bility of vehicles below category 1 and sub-divides each of the seven vehicle categories,especially category 7.

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Table 3. Vehicle Categories

Vehiclecone index Vehicles

Category range

1 20-29 The M29 weasel, M76 Otter, andCanadian snowmobile are theonly known standard vehiclesin this category.

2 30-49 Engineer and high-speed tractorswith comparatively wide tracksand low contact pressures.

3 50-59 The tractors with average contactpressures, the tanks with com-paratively low contact pres-sures and some trailed vehicleswith very low contact pres-sures.

4 60-69 Most medium tanks, tractors withhigh contact pressures, and allwheel-drive trucks and trailedvehicles with low contact pres-sures.

5 70-79 Most all-wheel-drive trucks, agreat number of trailed ve-hicles, and heavy tanks.

6 80-99 A great number of all-wheel-driveand rear-wheel-drive trucks,and trailed vehicles intendedprimarily for highway use.

7 100 or greater Rear-wheel-drive vehicles andothers that generally are notexpected to operate off roads,especially in wet soils.

b. Graphic Portion of Figure 60. The legendfor the shading of the three graphic portionsof figure 60 is given at the bottom part of thefigure. The white indicates excellent traffica-bility, the stippled good, the striped fair, andthe black indicates poor to intrafficable soil.The topography and soil conditions are shownin the following three graphs in figure 60.

(1) High topography, (higher areas ofthe terrain) wet-season condition.

(2) Low topography, (low areas of theterrain) wet-season condition (satu-rated).

(3) Low topography, high-moisture con-dition (wet, but below saturationpoint).

178. Use of Figure 60a. Mission. You have a rear-wheel drive

truck with which to deliver supplies crosscountry to another area. You have the follow-ing information:

(1) Vehicle cone index: 85(2) Topography: level high topography(3) Type of soil: clayey sands (SC)

b. Question. Is this trip feasible from thestandpoint of trafficability?

c. Procedure in Determining Trafficability.(1) You know that the vehicle cone index

of the truck is 85. Table 3 shows thevehicle to be in category 6. The ve-hicle cone index range (80-99) to theright of the category in table 3 andthe written description undervehicles verify the category of yourtruck.

(2) Locate vehicle category 6 at the topof figure 60.

(3) Find the vehicle cone index 85. Thenumber 85 must be interpolated onthe vehicle cone index line in thespace between 80 to 100.

(4) Find the soil type SC. This is givenunder Soil type symbol in the leftcolumn of the figure, and more con-veniently on the graphic portion ofthe figure.

(5) From the 85 (interpolated) on the ve-hicle cone index, move downward onthe high topography, wet-seasoncondition graphic rectangle to the areamarked SC. This area is stippled.Your legend at the bottom of figureshows that the trafficability for yourvehicle is good in this area. There-fore, the trip is feasible from thestandpoint of trafficability. Themarking around the soil type area onthe figure indicates that the traffica-bility interpretation on the chart hasgood reliability, as you may notein the legend. (Good reliability,based on analysis of data.)

d. Trafficability for Same Truck and SoilType on Low Topography, Wet-Season Con-dition. From the 85 (interpolated) on the ve-hicle cone index, move downward into the lowtopography, wet-season condition graphic rec-tangle to soil type SC. Note that the traffica-bility is good, as indicated by the stippling.Reliability of this trafficability interpretationis fair, based on judgment.

e. Trafficability for the Same Truck and

146


Same Soil Type on Low Topography, HighMoisture Condition. From the 85 (interpo-lated) on the vehicle cone index, move down-ward into the low topography, high-moisturecondition graphic rectangle to soil type SC.

Note that the trafficability is only fair. Hadthe vehicle cone index been a few points high-er, the trafficability would have been poor.The black on this graphic chart indicates poortrafficability and is a warning to "stay off."

147


APPENDIX A

REFERENCES

1. Field ManualsFM 3-10 Employment of Chemical and Biological Agents.FM 3-12 Operational Aspects of Radiological Defense.FM 5-15 Field Fortifications.FM 5-20 Camouflage, Basic Principles and Field Camouflage.FM 5-29 Passage of Mass Obstacles.FM 5-30 Engineer Intelligence.FM 5-35 Engineer's Reference and Logistical Data.FM 5-36 Route Reconnaissance and Classification.FM 17-36 Divisional Armored and Air Cavalry Units.FM 21-40 Small Unit Procedures in Chemical, Biological and Radiological (CBR)

Operations.FM 30-5 Combat Intelligence, C-1.(C)FM 30-10A Special Applications of Terrain Intelligence (U).(C)FM 30-15 Intelligence Interrogations (U).FM 30-16 Technical Intelligence.FM 31-10 Barriers and Denial Operations.FM 31-25 Desert Operations.FM 31-30 Jungle Training and Operations.FM 31-560 Combat in Fortified and Built-Up Areas.FM 31-60 River-Crossing Operations.FM 31-70 Basic Cold Weather Manual.FM 31-71 Northern Operations.FM 31-72 Mountain Operations.FM 55-8 Transportation Intelligence.FM 57-10 Army Forces in Joint Airborne Operations.FM 57-35 Airmobile Operations.FM 60-30 Embarkation and Loading-Amphibious.FM 100-5 Field Service Regulation-Operations, C-1.FM 100-15 Field Service Regulations--Larger Units.FM 101-5 Staff Officers' Field Manual-Staff Organization and Procedure.FM 101-10-1 Staff Officers' Field Manual-Organization, Technical, and Logistical Data.

2. Technical ManualsTM 3-240 Field Behavior of Chemical, Biological and Radiological Agents.TM 5-248 Foreign Maps.TM 5-249 Terrain Models and Relief Map Making.TM 5-297 Well Drilling Operations.TM 5-312 Military Fixed Bridges.TM 5-330 Planning, Site Selection and Design of Roads, Airfields and Heliports in

the Theater of Operations.

148


Pits and Quarries.Military Petroleum Pipeline Systems.Materials Testing.Control of Soils in Military Construction.Geology.Field Water Supply.Photographic Interpretation Handbook.Tactical Interpretation of Air Photos.

3. Army RegulationsAR 117-5AR 320-50

Military Mapping and Geodesy.Authorized Abbreviations and Brevity Codes.

TMTMTMTMTMTMTMTM

5-3325-3436-5305-5415-5455-70030-24530-246

149


APPENDIX B

OUTLINE FOR TERRAIN STUDIES

1. Purpose and Limiting ConsiderationsState the purpose and limiting considera-

tions under which the study is being prepared.This statement should include the scope ofthe study in area, time, and subject matter,and any information on the tactical situation,mission, or method of operations that is per-tinent to the study.

2. General Description of the Terraina. Synopsis. State briefly the impact of the

terrain on military operations.b. Climatic Conditions. Describe predicted

meteorological conditions for the period,based on climatic data. Present climatic datagraphically whenever possible. The require-ments of the study will determine the exactinformation presented and the manner ofpresentation.

(1) Temperature. Climatic data-givefrequency of occurrence of tempera-tures during period.

(2) Precipitation. Climatic data-statefrequency of occurrence of precipi-tation by type and amount.

(3) Winds. Climatic data-give frequencyof occurrence of winds of certainvelocities and direction. Use windrose.

(4) Visibility. Present graphically dataon times of sunrise, sunset, twilight,moonrise, and moonset. Describe ef-fect of fogs, mist, haze, and otherinfluences on visibility. State expectedvisibility by distance when applicable.

(5) Cloudiness. Describe when applicableand separate from precipitation andvisibility. Climatic data-give dataof frequency of occurrence and timeof occurrence of various cloud condi-tions.

(6) Humidity. Describe only when signi-ficant. Describe effect when combinedwith other weather elements, such asoppressive heat or wind chill.

(7) Electrical disturbances. Describe onlywhen significant.

c. Topography. If pertinent, describe thefollowing characteristics by written or graphicmeans. Recommend the use of a topographicmap overprint to emphasize particular charac-teristics.

(1) Relief and drainage systems. Useridge and stream lining, contour em-phasis, hilltopping, or relief shadingto outline the ridge and valley systems.Use numbers, words, or standardsymbols to indicate critical relief ordrainage conditions.

(2) Vegetation. Indicate location, type,and size of trees, density of planting,existence of undergrowth, and thelocation, type, and density of othersignificant vegetation.

(3) Surface materials. Indicate the typeand distribution of soils, subsoils, andbare rock in the area. Indicate theirtrafficability under various weatherconditions.

(4) Manmade features. Describe fully thesignificant manmade features. Includeroads, railroads, bridges, tunnels,towns, important buildings, fortifi-cations, or airfields when pertinent.

(5) Special features. Describe significantspecial features such as earthquakezones or active volcanoes.

d. Coastal Hydrography. Describe whenapplicable. Use graphic means whenever pos-sible.

(1) Sea approaches. Describe nature ofapproaches, bottom conditions, ob-

150


stacles, gradients, and coastal struc-tures. Use landing-area map to presentinformation graphically.

(2) Beaches. Describe dimensions, traffic-ability, and beach exits. Use land-area map to present informationgraphically.

(3) Tides and currents. Describe expectedtime of occurrence and stage of tides.Present graphically. Describe currentsby direction, velocity and duration.

(4) Sea and surf. Describe height of sea.Describe type of surf, width of surfband, height of surf, and expectedduration.

3. Military Aspects of the TerrainFrom an analysis of the factors of climate,

topography, and coastal hydrography, deter-mine the following military aspects and de-scribe them by written or graphic means. Useof an overlay to the basic topographic map isrecommended.

a. Tactical Aspects of the Terrain. The fol-lowing aspects are those basic to all tacticaloperations.

(1) Observation. Determine the effect ofthe terrain factors on observationfrom the ground, from the air, andby means of electric or sonic deviceswhen applicable.

(2) Fields of fire. Determine the effect ofthe terrain factors on the ability offlat- and high-trajectory weapons todeliver projectiles to a target. Con-sider nuclear weapons when applica-ble.

(3) Concealment. Determine the capabil-ity of the terrain to provide conceal-ment for men, equipment, and instal-lations. Consider the effect of terrainon concealment by artificial means.

(4) Cover. Determine the capability of theterrain to provide cover for men,equipment, and installations. Considerthe problem of cover from flat-trajec-tory, high-trajectory, and nuclearweapons when applicable.

(5) Obstacles. Determine the capabilityof the terrain to delay the advance ofmilitary forces or impede military

operations. Consider both natural andmanmade obstacles.

(6) Movement. From an analysis of soilstrafficability, natural and manmadeobstacles, and existing routes of move-ment, determine the ability of troopsand equipment to move through anarea. Use standard color code to de-scribe movement conditions. Use spe-cific terms of movement wheneverpossible; i.e.-vehicular, cross-coun-try, and foot.

(7) Key terrain features. From an analy-sis of the terrain and of friendly andenemy methods of operations, indicatethose terrain features which appearto be critical, such as a dominantheight, a highway, a communicationcenter, or an airfield.

(8) Avenues of approach. From an analy-sis of all terrain factors affectingcapabilities to move men and materiel,determine the avenues of approach tothe objective. Consider existing routesof movement, possibilities of cross-country movement, and amphibiousor airborne or airmobile operationswhen applicable.

b. Engineering Aspects of the Terrain. Deter-mination of the following military aspects isessential to planning the engineer phase of op-erations. Include these items in written orgraphic form as overprints or overlays.

(1) Construction sites. From an analysisof surface material and other terrainfactors, determine areas suitable forconstruction of roads, airfields, build-ings, underground installations, sur-face defensive installations, or others.

(2) Construction materials. From ananalysis of surface materials andother terrain factors, determine theprobable location of rock, gravel,sand, or other natural constructionmaterial.

(3) Water supply. From an analysis ofthe drainage system and subsurfaceformations, determine the probablelocation of potable water and watersuitable for construction use.

151


4. Maps and Charts (as appropriate)a. Topographic.b. Trafficability.c. Landing (where applicable).d. Special maps (when needed).

(1) Geological.(2) Soils.(3) Hydrographic charts.(4) Town plans.(5) Road.(6) Joint operations graphic.

152


APPENDIX C

SAMPLE TERRAIN STUDY

Headquarters 15th ArmyWestern GermanyJanuary 1945

1. PURPOSE AND LIMITING CONSIDERATIONSa. Purpose. This terrain study considers the area to the south and east

of COLOGNE, Germany, for February and March. General boundaries forthe zone are the towns of JULICH on the ROER RIVER (3145) andZULPICH (3418), and the RHINE RIVER north and south of COLOGNEas shown on inclosure 1 (fig. 61). Elements of Fifteenth Army, consistingof armored and infantry units, are located west of the ROER RIVERand presumably will operate in the area with the general mission ofadvancing northeastward to the RHINE RIVER.

b. Limiting Consideration. Information presented is based on dataobtained from maps, intelligence documents, climatic study, and interroga-tion. Ground reconnaissance has not been made, nor have the effects ofbombing been considered.

2. GENERAL DESCRIPTION OF THE TERRAINa. Synopsis. The area during this period of the year provides favorable

conditions for military operations. It is highly populated mixed farm andindustrial region. Construction sites and materials are available and thecommunication system is excellent. Movement across the RHINE RIVERis canalized at BONN and COLOGNE. Obstacles are the ROER and ERFTRIVERS and the VILLE RIDGE. Conditions influencing movement aresensitive to precipitation.

b. Climate Conditions. See inclosures 2, 3, and 4 (figs. 61-64).(1) Temperatures will present problems to the effective operation

of troops in the field. Inclosures 2, 3, and 4 give compiled tempera-ture data.

(2) Precipitation in some form normally occurs every second day.Wet soils are common. Snowfalls ordinarily do not exceed 9 to 11centimeters (6 or 7 inches). Ice, if present, is thin and will notsupport a man.

(3) Wind direction and velocity are given by the wind roses in in-closures 3 and 4. Winds from the east are usually accompaniedby severe temperature drops.

(4) Visibility factors are listed in inclosures 2, 3, 4 and 5. Fog occursrarely at this time of year, despite the high relative humidity.The high frequency of moderate to fresh winds favors theformation of low clouds rather than fog.

153


c. Topography.(1) Relief is low and gently rolling with only two exceptions: the

southwestern portion of the map (HOHE VENN) has steepwooded hills and highlands dissected by deep valleys; and a lowhilly ridge, hereafter known as the VILLE RIDGE, exists be-tween the ERFT RIVER and the RHINE RIVER. This area isdiscussed in detail on the back of the map and later in this study.

(2) Drainage. Streams cross the region generally from southeast tonorthwest. The ROER RIVER is approximately 80 feet wide,with no fords, and can be flooded by release of water impoundedin dams to the south. The ERFT RIVER, or canal, meandersthrough several channels in its flood plain. These channelsaverage 6 to 9 meters (20 to 30 feet) in width and .6 to 1.5meters (2 to 5 feet) in depth. In many places, the river channelsare flanked by marshy flats which are drained through numerousdeep ditches.

(3) Vegetation. The area is largely devoted to agriculture andpasture but scattered forests do exist, and these are delineatedon the map with notes as to density, type, and approximate bollsize. Trails and unimproved roads allow restricted passage eventhrough the dense forests. At this period of the year, the groundwill be fallow or in low cover crop which will increase its traffic-ability. Trees are scattered throughout the numerous mine pitsin the area.

(4) Surface materials. The region is generally covered by a loamy soiltending toward sandy soil in the south. In the VILLE RIDGEarea, the original soils have been stripped off during mining,exposing sandstone and shale. Stream valleys are composed offine grained silts in the northern reaches and change to sandymaterial upstream to the south. The soil immediately west ofthe RHINE RIVER is composed of sandy well-drained material.Surface materials are discussed further on the back of the move-ment map.

(5) Manmade features. The manmade features studied include roads,railways, bridges, airfields, towns, and strip mines.

(a) An excellent network of roads exists. Only the primary sys-tem, that with a route classification (FM 5-36) of X is shownon the map. In addition, secondary roads of general routeclassification connect many of the villages. Free egress fromroads for cross-country movement is possible in most places.

(b) Rail communication, as shown on the map, is very good. As aa supplement to the standard-gage system, considerablenarrow-gage lines exist, particularly in the VILLE RIDGEregion. Marshalling yards are located at DUREN, BONN, andCOLOGNE. The tunnel on the double-tracked route betweenDUREN and COLOGNE is a vulnerable point, but may be by-passed through alternate routes.

(c) The classification of bridges along the primary-road system is65. Important bridges are indicated on the map with theclassification noted if lower than the general class. Bridges onthe secondary-road system have a general classification of 55.

154


(d) This area contains a large municipal airfield capable ofhandling heavy-cargo aircraft. These have been marked onthe map. Also shown are three landing strips which can beused by assault aircraft. Sections of primary roads and auto-bahns may be utilized for light Army aircraft strips.

(e) Most urban areas are well built-up with stone and masonrybuildings. Streets, except for boulevards or freeways, are nar-row, and may permit only one-way traffic to trucks and tanks.All but the larger cities may be bypassed easily.

3. MILITARY ASPECTS OF THE TERRAINa. Tactical Aspects.

(1) Observation. Observation throughout the area is generally good,although there are small areas of defilade. The VILLE RIDGEaffords excellent observation of the lowlands to the east andwest. The HOHE VENN area provides good points for observa-tion of the ROER RIVER valley. Small hills afford tacticalobservation in the plains section. Aerial observation will be ex-cellent, except where woods obscure the ground.

(2) Fields of fire. The area provides generally good fields of fire forall weapons with two exceptions. The broken terrain of theVILLE RIDGE and the HOHE VENN limits fields of fire forflat-trajectory weapons within the ridge masses themselves.However, fiat-trajectory weapons situated on these ridges cancommand their lowland approaches very effectively.

(3) Concealment. The mixed forested areas give good concealmentfrom both air and ground observation. The broadleaf forests arebare of leaves during February and March and offer only limitedconcealment. Farming practices in this part of Germany aresuch that little concealment is possible in the winter cover crops,but the many farm buildings and small villages afford good con-cealment for small units.

(4) Cover. Principal cover is offered by the stone structures thatmake up the cities and farm communities. In the VILLE RIDGEarea, some cover can be found in the mine tunnel.q

(5) Obstacles.(a) The ROER RIVER under normal conditions will offer only

minor problems to an assault crossing. Opening or destroyingthe ROER DAM will flood the ROER VALLEY. If this isdone, it will take at least a week for the ROER RIVER to re-cede, and 2 to 3 weeks for soils trafficability to return to normal.

(b) The ERFT VALLEY, with its drained swamps and manycanals, will restrict movement to roads in most areas. The riverchannels themselves are not a serious obstacle to infantry;however, a long thaw, which is quite possible in March, or anunseasonal rain can make them unfordable to foot troops. Thereare also lignite pits west of Koln along Erft River.

(c) Wooded areas may restrict vehicular movement to narrow un-improved roads but are passable for infantry under normalconditions.

(d) The VILLE RIDGE forms an obstacle of major importance tovehicular and foot movement. It may be easily defended against

155


a superior force, affording the defender excellent observationand concealment in its woods and extensive mine workings.

(6) Movement. This is indicated on the movement map (fig. 61).The area as a whole provides very good movement during dryweather, and fair to doubtful movement during periods of heavyprecipitation.

(7) Key terrain features.(a) The VILLE RIDGE dominates the lowlands to the east and

west of the hill mass. Routes crossing the VILLE RIDGE arerestricted to the roads because of the extensive pits, quarries,and spoil heaps left by coal-mining operations.

(b) The HOHE VENN highlands southwest of DUREN overlookthe adjacent ROER RIVER valley. In this region heavy forestsand steep slopes restrict vehicular traffic to the roads.

(8) Avenues of approach. The main highways from the ROERRIVER toward COLOGNE offer good avenues af approach fromthe southwest, and represent the bet routes for breaching theVILLE RIDGE. The best avenues of approach would be to thenorth of JULICH-COLOGNE highway where the VILLERIDGE may be flanked and cut off. The secondary road and railnet is adequate for support of an armored attack. The VILLERIDGE may be flanked from the south in the vicinity of BONN,but here armored operations will be somewhat restricted andcanalized by dense forests, and by the constriction of the corridorbetween the VILLE RIDGE and the RHINE RIVER.

b. Engineering Aspects of the Terrain.(1) Construction sites. With the exception of the mining dumps, the

southwestern highlands, and the river flood plains, the area iswell suited for the construction of roads, airfields, cantonments,depots, and other military surface structures. The land is leveland open, the communication net is excellent, and the soil hasgood stability and bearing capacity. The HOHE VENN highlandis better suited for underground facilities than the plains area.Solid sandstone layers are useful as floors and roofs here, andground water will not be as troublesome as in the flatlands.

(2) Construction materials.(a) Natural materials. Quarries and gravel banks are available

for stone and aggregate at many places. The terraces along theRHINE and ROER RIVERS are good sources of gravel andsand, while sandstone suitable for construction purposes canbe quarried west of ZULPICH. Broken rock consisting ofsandstone, shale, and soil is piled in the VILLE RIDGE dumps,and west of DUREN. Forests supply adequate quantities ofstanding timber to cover any foreseeable needs. Small localsawmills may be useful in cutting the timber for use.

(b) Manufactured materials. The heavy industrial buildings in theVILLE RIDGE and COLOGNE areas are good sources of con-struction steel, lumber, and similar materials needed by engi-neers. In addition, a large network of mine railroads existsthroughout the pits and may be utilized for material.

156


(3) Water supply. An adequate field water supply may be obtainedfrom the streams and wells of the area. Civilian water supply onfarms is obtained from wells, and in cities through municipaldistribution plants and systems which draw water from themajor rivers. Emergency water supplies may be drawn fromthese sources.

5 Inclosures:Inclosure 1.Inclosure 2.

InclosureInclosureInclosure

3.4.5.

Movement map of Cologne area (fig. 61).Climate conditions Cologne, Germany, for February andMarch.Climatic data for Cologne area for February (fig. 62).Climatic data for Cologne area for March (fig. 63).Ephemeris for Cologne area for February and March(fig. 64).

Figure 61. Movement map of Cologne area.

Figure 61-Reverse.

(Located in back of manual)

157


CLIMATIC DATA FOR COLOGNE AREA, GERMANYFEBRUARY

PRECI PI TATION TEMPERATURE WIND ROSE TACTICALAIR SUPPORT

- N S -S

e -..,E. .. -

._.:_.... ,_...

.. i

0'4 Y

t' fl- -.. nI

Figure 62. Climatic data for Cologne area for February (Inclosure 3 to app D).

CLIMATIC DATA FOR COLOGNE AREA, GERMANYMARCH

PRECIPITATION TEMPERATURE WIND ROSE

A. . - -._ ...

', ...1 ........ .I...

-C -m77m---

u:-..r_.ad. ...... ;0'.% -

M....

TACTICALAIR SUPPORT

Figure 68. Clinmatic data for Cologne area for March (Inclosure 4 to app D).158

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Inclosure 2. Climatic Conditions, Cologne, Germany,for February and March

Feb - Mar

Temperature ('F.):Mean maximum __.- . ....._____ 43 49Mean minimum _ .-------------- 33 37Absolute maximum _----._-_____-66 72Absolute minimum .------------ 0 13Number of days with:

Minimum-32 F .- ....._ _. 10 6Maximum-32*F ...-------- 2 0.4

.Precipitation (CM):Mean .-.-.. _.__._ 4.09 4.39Maximum ..-..... ..... 11.88 10.31Minimum .---------------- 0.4 .7Maximum in 24 hours . ... 3.15 2.06

Mean number of days with:Snowfall 0.01CM __.- . ..____. . . 6.4 5.9Snow on ground .-.............. 5.3 2.0Fog ….... ........ 1.2 :1.4Wet soil ______________________ 14.2 13.2Clear skies _______.____________ 3.2 3.1Partly cloudy skies .------------ 14.7 19.1Cloudy skies __---------------- - 10.3 8.8

Mean relative humidity (%):0700 LST --------------------- 84 82.1400 LST -----------------_-__ 74 67.1900 LST .-------------------- 82 76

160


APPENDIX D

SAMPLE CLIMATIC STUDY

GeneralThis study is divided into four parts, each

having a different operational aspect: amphibi-ous, airborne, airmobile, and overland in twodiffering climatic regions. The studies and ac-companying data do not refer to any exactgeographic locations, but are offered only as aguide for format and content.

a. Information Sources. Source material forsuch studies is usually drawn from climaticsummaries on file at the Climatic Center, Head-quarters Air Weather Service, from the Na-

tional Intelligence Survey (NIS) sources, andfrom weather summaries on file at the U.S.Weather Bureau or Congressional Libraries. Inthe field, information of a climatic nature maybe obtained from local Air Weather Servicedetachments or a national meteorological serv-ice office. The climatic study is designed toprovide a first estimate of weather factors af-fecting military operations and should not beregarded as an operational forecast which nor-mally is supplied by other Air Weather Servicedetachments.

Figure 65. How to read a wind rose.

161


b. Wind Rose. The agency requesting cli- rose is shown in figure 65. The wind rose makesmatic data from Air Weather Service shouldspecify whether the wind speed data is desiredin kilometers, miles, or knots per hour. Windspeed data is shown in compact form by meansof a wind rose. The method used to read a wind

use of the Beaufort scale, which is a windscale in which the force of the wind is indi-cated by numbers with corresponding descrip-tive terms. These terms are commonly used bythe U.S. Weather Bureau (table 1, chap. 4).

Part I

Climatic Factors Affecting an Overland Operation in the RegionSurrounding OBJECTIVE ONE During May

In terms of general climate, OBJECTIVEONE area has a maritime-type climate, char-acterized by cool, humid winters and mild,comparatively dry summers. The month ofMay represents a portion of the transitionperiod between these two characteristic sea-sons.

In the absence of meteorological informationfor the exact location involved, combined datafrom adjacent areas, both north and south,were considered to be representative of theclimate of OBJECTIVE ONE area and are pre-sented as appendix material in tabular (tableD-1) and graphical (fig. 66) form.

Table D-1. Overland Operation OBJECTI'VE ONE-May

Temperature ('F.):Mean Maximum ___-_______._______ 62M ean -------------------------- - 650Mean minimum _-.________________ 38Recorded Extremes . ............. 77 to 31

Mean Number of Days with:Fog _-_-__-__-_-_-_-_-______ _ _ 1Thunderstorms ------------------ 0Rain _..._-------------------- 8

Temperature during May is usually condu-cive to moderate to strenuous activity. Nor-mally, temperature averages approximately50 ° F., with a moderate diurnal and monthlyrange. Minimum temperatures, especially dur-ing the first portion of the month, in valley

areas or close to the ground surface are fre-quently in the mid 30's during early morninghours.

Rainfall is light, averaging 5 to 6 centime-ters (2 to 21/2 inches) for the month. Thisamount, well distributed in time (the maxi-mum reported for any 24-hour period is 2.5centimeters (11/2 inches)), should not createproblems associated with soil moisture andwould be sufficient to minimize dust conditions.Snow accumulations on the mountains andpasses east of the area melt at this time andprovide a source of fresh water for the localstreams. Flooding of these streams is unusual.

Relative Humidity is high throughout theday, averaging 80 percent to 85 percent. Di-urnally, the variation is relatively small, 10percent to 20 percent. Although relative humid-ities average quite high, the incidence of fogand other forms of restricted visibilities isquite low; about 5 percent of the time the visi-bility is less than 4 kilometers (21/2 miles).

Cloud cover and visibilities are well suitedfor tactical air support.*

Winds are primarily from a westerly direc-tion, southwest through northwest, with anaverage speed of 7 to 10 knots. Approximately25 percent of the time the winds are less than3 knots.

* Minimum ceiling and visibility requirements depend upon thetype of support and the equipment involved, and upon the type ofterrain over which this support must operate.

162


CLIMATIC DATA FOR OBJECTIVE

MAY

PRECIPITATION

ONE

TEMPERATURE (F)

APPROXIMATE NUMBER OF DAYSIN WHICH SPECIFIED AMOUNTSMAY BE EXPECTED TO OCCUR6

.0 ·

INCHES

8 0TRECORDED MAXIMUM

70-

60--MEAN MAXIMUM

50_-MEAN

4 0 - MEAN MINIMUM

3 0 J-RECORDED MINIMUM

WIND ROSE

WIND SPEED SCALE

CALM4-12, 3-24 255-38: KNOTS0-3, I

PERCENTAGE FREQUEN

10I IO I0

ICY SCALE

20 30

Figure 66. Climatic data for OBJECTIVE ONE-May.

163


Par

Climatic Factors Affecting an Amphibious Landing onOBJECTIVE TWO During May or June

Complete meteorological observations on theisland were made only during a brief periodduring World War II. Plantation records forlonger periods of record have been used in ar-riving at precipitation estimates. Climatic dataare presented as appendix material (table D-2and figs. 67 and 68).

Table D-2. Amphibious Operations OBJECTIVETWO Island-May and June

Temperature ('F.):Mean Maximum ........Mean -_---------------Mean Minimum ........Recorded Extremes ------

Mean Number of Days with:Thunderstorms .........Precipitation ___------ --

1.3 centimeters-0.5 inch .......

4.8 centimeters0.6 to 1.9 inches ____

5 centimeters-2.0 inches ._--------

May888175

93 to 73

817

12

4

1

June908276

95 to 74

Climatically, OBJECTIVE TWO Island hasall the typical tropical characteristics withheavy, shower-type rainfall and a small diurnaland seasonal temperature range. Since theisland is affected by the monsoon wind, theMay-June period is one of transition, duringwhich winds are normally light and variable.

Temperature conditions are not conducive tohuman activity, and the daily range of tem-peratures is insufficient to alleviate this humandiscomfort at night. The mean temperature is

approximately 80° F., with a maximum dailyrange of about 20 Fahrenheit degrees.

Humidity is constantly high and coupledwith the warm temperatures creates problemsof material storage and supply, in addition toadding to human discomfort. Mean relative hu-midity is approximately 80 percent, with onlyslight variation diurnally.

Visibility is seldom restricted by weatherfactors except during brief periods of heavyshower activity; however, dense vegetationlimits ground visibility severely unless someform of clearing has taken place.

Precipitation is of the brief, heavy shower-type that usually occurs during the afternoonon an average of 1 out of 2 days. Thunder-storms are quite frequent, with an average of8 storms per month. Although total precipita-tion is highly variable from year to year, it ismore than adequate to keep soils moist, supportheavy vegetation, and present vehicular trans-port problems. Maximum precipitation in 24hours reported for the island during this periodwas 18 centimeters (7.2 inches) during May.

Winds are light and variable, except duringheavy showers; however, during June thesoutheast monsoon is being established andsoutheast winds become more predominant. Inthe forested areas, winds are usually verylight or calm, but along coastal strips theyaverage about 5 knots. Typhoon winds are notconsidered a threat to operations this early inthe season.

164


CLIMATIC DATA FOR OBJECTIVE TWO )MAY

PRECIPITATION TEMPERATURE (E)

APPROXIMATE NUMBER OF DAYSIN WHICH SPECIFIED AMOUNTSMAY BE EXPECTED TO OCCUR

12 //// I 100O

90-- RECORDEP MAXIMUM

-MEAN MAXIMUM

80oMEAN

70-

-MEAN MINIMUM-RECORDED MINIMUM

WIND ROSE

WIND SPEED SCALE

CALM 4-12 :13-24125-381 KNOTS0-3 ,

PERCENTAGE""10 0T

I0 0

FREQUENCY SCALE10 I 20 3010 20 30

Figure 67. Climatic data for OBJECTIVE TWO-May.

Part III

Climatic Factors Affecting an Airborne-Airmobile Operation inthe Vicinity of OBJECTIVE THREE During September

For the purposes of this report, it was as-sumed that paratroop operations would be car-ried out only with a ceiling value equal to orgreater than 305 meters (1,000 feet), visibility

equal to or greater than 4 kilometers (21/2miles), and wind speed less than 13 knots. Onthis basis, favorable weather occurs most fre-quently during the midafternoon. Unfavorable

165

¢6

INCHES


CLIMATIC DATA FOR OBJECTIVE TWO

JUNE

PRECIPITATION

APPROXIMATE NUMBER OF DAYSIN WHICH SPECIFIED AMOUNTSMAY BE EXPECTED TO OCCUR12

4

TEMPERATURE (F)

100-

-RECORDED MAXIMUM

90- -+MEAN MAXIMUM

80-

70-INCHES

- MEAN

-MEAN MINIMUM-RECORDED MINIMUM

WIND ROSE

WIND SPEED SCALE0/. _ PERCENTAGE FREQUENCY SCALE

M I m........I I I I

CALM: 4-12 :13-241253KNOTS 10 0 10 20 300-3 1 I

Figure 68. Climatic data for OBJECTIVE TWO--June.

conditions increase gradually until early morn-ing hours when adverse weather occurs ap-proximately 25 percent of the time. Tacticalair support, depending upon the type needed

and equipment utilized, should be able to op-erate 70 percent to 80 percent of the daylighthours (table D-3 and fig. 69) .

166


Table D-3. Airborne Operation OBJECTIVE THREE- ture is large, but normal temperatures areSeptember

Temperature (°F.): SeptemberMean Maximum .-............... 67Mean ..-. . ...__________________ 58Mean Minimum . .-. ........__.__ 50Recorded Extremes . ................ 87 to 38

Mean Number of Days with:Thunderstorms -___ --__.. _.__________- 3Precipitation --------------- _-___ 19

2.54 millimeters (0.1 inch) ..... 92.54 to 12.70 millimeters

(0.1 to 0.5 inch) .------------- 612.70 millimeters (0.5 inch) ___-___ 4

Precentage Frequency, by Hour, of WeatherFavorable for Paradrop Operations(Ceiling 305 meters (1,000 ft.)), Visi-bility 4 kilometers (241 miles, Wind 13ft.)

0800 LST 74%1400 LST 96%1900 LST 91%

Temperatures are not extreme during thisperiod and should not present problems of hu-man comfort. The extreme range of tempera-

quite moderate with mean maximum of 67° F.and a mean minimum of 50° F.

Precipitation, in the form of drizzle, lightrain, or showers, occurs on the average of 2days out of 3, giving an average Septemberrainfall amount of approximately 6.35 centime-ters (21/2 inches). Heavy rainfall is infrequent,but when it occurs, poorly drained areas be-come flooded and trafficability problems areintensified.

Fog restricts visibility to less than 800meters (one-half mile) on 1 day of 10, mostoften during the early morning hours. Duringthe afternoon and early evening the possibilityof restricted vision caused by air pollutant iseven less.

Winds are most frequently from the north-west (see wind rose), with about 10 percentof the observations showing wind speedsgreater than 13 knots. Diurnal variations inwind strength or direction appear negligible inthis particular area.

Part IVClimatic Factors Affecting an Overland Operation in

the Vicinity of OBJECTIVE FOUR During February

Climatically, the objective area has a marineclimate, which implies mild, cloudy, and humidweather (table D-4 and fig. 70).Table D-4. Overland Operation OBJECTIVE FOUR

-February

Temperature (°F.):Mean Maximum _________________.Mean -- ---------------------Mean Minimum ________________.___Recorded Extremes ____---------

Mean Number of Days with:Precipitation -. ------

2.54 millimeters (0.1 inch)2.54 to 12.70 millimeters

(0.1 to 0.5 inch) --____________12.70 millimeters (0.5 inch) ___.__

Snowfall .........................Snow on ground _-_.________________

Mean Relative Humidity (%)0700 LST1400 LST1900 L ST --------------------------

February453832

64 to 10

857180

result of the moderating effect of the water onthe migratory air masses. However, alternatefreezing and thawing of the normally water-soaked soil surface is common, creating prob-lems of vehicular movement due to rapiddeterioration of natural surfaces.

Precipitation in the form of rain, drizzle,and/or snow occurs on approximately one-halfof the days during the month. Snowfall isusually small in amount, but is apt to be wet,heavy, and clinging; possibly resulting in de-struction of overhead wires and some vegeta-tion. Snow cover is usually shortlived, beingdestroyed by the frequent warmer rains. Soilsare usually water soaked; only during excep-tionally cold winters does the ground freeze toany depth.

Fog occurs on 4 to 5 days during the monthand is usually quite dense, persistent, andwidespread, restricting visibility to severalhundred meters and precluding any tactical airsupport. Cloud cover is usually present, but

167

Temperatures usually are not severe, as a


CLIMATIC DATA FOR OBJECTIVESEPTEMBER

PRECIPITATION TEMPERATURE (F)

APPROXIMATE NUMBER OF DAYSIN WHICH SPECIFIED AMOUNTSMAY BE EXPECTED TO OCCUR

9 .

ciw

Cd

9 0 TRECORDED MAXIMUM

80-

7 0 --MEAN MAXIMUM6 0 - -MEAN

50- -MEAN MINIMUM

4 0 -RECORDED MINIMUM

30-

WIND SPEED SCALE

CALMI 4-12 13 - 2425- 3 KNOTS0-3 1 1

PERCENTAGE FREQUENCYI"'l""l i I

10 0 10 20

Figure 69. Climatic data Objective ThreeSeptember.

168

THREE

SCALE

30


CLIMATIC DATA FOR OBJECTIVE FOUR

FEBRUARY

PRECIPITATION

APPROXIMATE NUMBER OF DAYSIN WHICH SPECIFIED AMOUNTSMAY BE EXPECTED TO OCCUR9 I I .

U,

C3

o;

INCHES

TEMPERATURE (OF)

70RECORDED MAXI

60

50MEAN MAXIMUM

40 MEAN

30 MEAN MINIMUM

20

I0 'RECORDED MINIM

IMUM

IUM

WIND ROSE

WIND SPEED SCALE

CALM' 4-12 :13-24125-38,KNOTS0-3, , , i

PERCENTAGE FREQUENCY SCALE1I""1"I' 1 1

10 0 10 20 30

Figure 70. Climatic data for OBJECTIVE FOUR-February.

normally the effective ceiling is about 610 ern direction, light to moderate in force withmeters (2,000 feet). infrequent gale-force winds associated with

Winds are predominately from a northwest- strong frontal passages.

169


APPENDIX E

NATURAL TERRAIN FEATURES

The natural terrain features shown in A, B, and C, figure 71 willserve as a guide to producers and users of terrain studies. A few of theterrain features identified on the figure may be known in some regionsunder different names because of local usage.

170


APPENDIX F

DEPARTMENT OF DEFENSE INTELLIGENCE INFORMATION

REPORT FORMS 1396 AND 1396C

Department of Defense intelligence information will be reportedon DD Form 1396 and DD Form 1396c. These forms are available throughregular supply channels.

171


INDEX

ParagraphAerial photographs . ..-. .......173Aerosols . . .. . . ................36fAgencies, intelligence .-----------23Air support _-_-___.---_-------.60gAir temperature .---------------25Air Weather Service --- ___. - __--30a, 34eAirborne operations .. .......... 141Airfields . . .....................113, 114Airmobile operations …-_____-____ 141All weather route ___ . ........_--95bAlluvial plains -___ .. .........55Altocumulus clouds _----_---_--- 2 9g(2)Altostratus clouds . ..... -- - --.- 29g(1)Amphibious operations ___-__.. _ 140Anaglyph ----.. -------------18d( d(2)Antarctica -----------------_--- 54c(2)Arctic regions ___________._____: O0Assault landing _________-______70fAtmospheric pressure ----------- 26Atolls _____-- -__- -__ -___.____._-73dAvenues of approach _----------49g, S0g,

60e, 90e,95c(l),137, 162

Barrier reefs --. _______---------73cBarriers __ ….____-_____________ 136cBeach profile __-_______....___.167eBeaches ________________..______70, 71,

168cBearing capacity of soils .- ....... 174bBiological agents .--------------48d(6), 49iBoulders __-____._______________55b (4)Bridges -.. ____________________97Broadleaf forest ___._____.___84cBuildings ............_......... 122, 125b

Catchment basin -- _._._. .......62bChain, mountain __-_-_-_---_____57dChemical agents -- ____-.. -- _._.. . 48d(6), 49iChief of engineers ____- ___-__8cChinook wind -_ . ..............27dCirrocumulus clouds . ........29f(3)Cirrostratus clouds . .._. ......29f(2)Cirrus clouds ___ ….._____._____-_ 29f(1)City areas .-................ 122dCivilian oil pipelines .......... d.10 6dClay .--------------------------76eClimate, effects of ------- __-- - 54b, 155,

170Climate, examples:

Continental . ...............44bDesert .--------------------42b

Page Paragraph143 Dry ____…__________… ___.. .4226 Humid .--------------------44b11 Marine west coast ___… ..___. 43d62 Mediterranean …--.--- ..... 43b13 Mesothermal . ..............43

21, 24 Microthermal __.__-___ .. ._44127 Middle latitude ---- ___------42d105 Polar . ....................465127 Savanna ______-- ___-_------41b94 Subarctic ..._-. . ....... . .. 44e52 Subtropical ____.-.._______ 43c19 Tropical .. .................4119 Climate and terrain . ...........40b

126 Climatic study:10 Preparing -______________.4752 Sample ___---________-___. App D

40 Cloud cover symbols .-----------2975 Cloudiness ..................- 3814 Clouds .... ______________.____-___29, 38,77 165b(6)

40, 42 Coastal plains _-______..___ ...53d, 55e(1),62, 91, 140d

94, 122, Coastal ridge .. ................140e138 Coast lines ____…_________.._.._-74a77 Collection agencies, intelligence -- 23

122 Collection effort, intelligence __. .13141 Communication, lines _____- .____20c, 49h,

73, 75, 60f, 94,141 123e143 Communication maps .-._____ __17a(3)

38, 40 Compartments . .................13855 Cone index, vehicle . ............ 17496 Construction:85 Effects of vegetation .-.... 90f

112, 116 In hills and mountains __60iMaterials-164, 1665

60 Problems . ...-. ...........55, 122cContinental climate .-........ 44b

38,40 Contour emphasis __-. .__.____.15616 Coral reefs ----... ___._________73

Cordillera ___…___-------_ .......57e1919 Corridors . . ................13917 Cover and concealment .-- - 48d(3),

112 49f, 50e,101 60c, 90c,81 123c,

52, 134, 135, 160142 Crops, field . ....................89a,

Cross-country movement .--.--- 16333 Cycle, intelligence _….-------- 1231 Cyclones, tropical . ............. 32c

Page31333231313231333033323029

35161

1626

16, 26,135

48, 57,126126

78117

11, 40,62, 93,

1138

123143

9163

13952, 112

331357760

123

37, 40,42, 62,

90, 113,121, 138

89138

722

173


Paragraph Page Paragraph PageDams . . .... ....................119b 109 Hydraulic structures . ......._ 119 109Deciduous trees __________.____.83cDefense Intelligence Agency -__--8aDelta plains … -_________________-53eDesert climates __ 42bDesert drainage ________-___-___63gDeserts ------------ _48Determining trafficability __…-__..178cDew point .---_ _____ -- _____---28cDispatch route ________. … .______95c(5)Dissemination of intelligence __..__16Distribution of rainfall __….______39Divides, mountain _ .- . ......._..58cDocuments, enemy ______-_____..21Drainage ......________ ________ 62, 156bDrift plains ___________________-53h(2)Drop areas ___…_________._______141cDrumlins --------------_- 5____.53h(2)Dry climates __________________42Dunes _.-....._________.___.. 71b, 140f

845

48316635

14616948

266111

64, 13549

1274931

75, 126

Engineer:Intelligence functions -_.....11 6Intelligence Studies _________20b 11Terrain Detachment ________153 133

Ephemeral streams .-----------63c 66Estimate, terrain _-_____________4 4Evaluation of railways .- ...__._. 100 97Evergreen trees _________…_____.83c 84Example of climatic study ____- App D 161Example of terrain study _______ App C 153Extreme climates __- _-_. _______41, 42b, 30, 31,

45 33

Fair weather route .------__--- 95b(3) 94Fields of fire .-..........____. .48d(2), 37, 39,

49e(1), 42, 61,50d(2), 90, 120,60b(2), 13890b(2), 134,159b

Flood control …_________-_______- 119a 109Flood plains _____________.______53f 48Foehn effect …2_______ ...______- 27d 16Fog ____________ ____________31 22Foothills __…_-____…_… . .._______….58d 61Forecasts, weather ______________33 22Forests .-.........._____ _____.84, 85, 85, 86,

86 87

Glaciers _- -_______-____________ 66 67Glacial plains _______-_--______.53h, 49, 58

55e(4)Glory-hole mining .... ....109d 103Grasses .-----________________ 88 88Gravel __-----_________ ________ 76b 81Gravity springs ______-_-______67c(1) 70Greenland, marginal features ____54c(1) 52Ground water __________________67, 145 69, 129

High-latitude forests .- . . ..______ 86 87Hills -5.. . ..._______________.__ 59, 145d 61, 130Humidity ______________________28, 37, 44b 16, 26,

155b(5) 33, 135

Hydrography .- 1----__--------__156bHydrologic circle .._. ........_.67a

Ice front …__.. ................ 66cIce cap ________-__-_____- -___46Index, cone vehicle _ . .......... 174Information requirements,

terrain:Airborne …. .............. .141bAirfields . .................. 115Airmobile ................- 141bBridges ....................98Buildings _ …_. ____________126Drainage ---------------- 69Hills and mountains .-._. 61Hydraulic structures ........ 121Inland waterways .--------- 103Landing areas .-......... 75M ines ------------------ -_ 110Non-urban areas -____. .... 131Petroleum and gas __._____ 108Plains and plateaus .----___ 56Quarries and pits ___.- . .___112Railways -.............. - 101Roads .----------------__96Rock . .....................81Soils . . ......._._.___ . .___ 79Urban areas .___._._____ 124Utilities ____ .._____ ______ 128Vegetation …_____.____ ___91Water supply _ .- . .....___ 147Water terminals .------____ 118

Inland waterways -_____ ._____ 102Intelligence:

Collection --------------- -13Cycle _. . ...___. _________ 12-16Dissemination _.-........__ 7a, 16Officer __…_________________ 10Processing ................ 15Reports ---.------------ ___ 20Strategic .---------------__ 6bWeather _ ___--- _-__---___-- 34

Intermittent streams … ......____ 63bInterrogation of prisoners .------22

Jungles __-------------------- 49

Karst plains ..- …._______________53k, 55c(7)Key terrain …._._.__…___ .__-____48d, 49d,

60a, 90a,133, 158

Lacustrine plains __ …_…. . ___.53i, 55e(5)Lakes ___-......_____..______ 64, 68d,

144dLandforms … ..................51b, 53Lateral route __--_______...... 95c(2)Lines of communication _ ….....20c, 49h,

60f, 94,123e

Locks … . .......................119dLoess plains ___... ._____ ._____53i, 55e(6)Low-latitude forests ..… ........ 84

13569

6834

143

12710612796

1167263

1119980

104118102

6010598958483

11411791

130107

98

77, 85, 8

67

114

236411

38

50, 6037, 39,61, 89,

120, 138

50, 6066, 71,

12944, 45

9411, 40,62, 93,

113110

50, 6085

174


ParagraphMangrove swamp . ...........-. . 84bManmade terrain features --..... 92Maps . . ......................17, 172Marine west coast climate ...... 43dMarshes and swamps ------------ 65, 68eMaximum tractive effort -------- 174mMeandering river . .............531Mediterranean climate ---------- 43bMediterranean scrub ------------ 85bMelt water . ................66fMesothermal climate … ...43Microthermal climate … ...44Middle-latitude climate ........42dMiddle-latitude forests ........85

Military aspects:Bridges . ..................98Buildings . .................126Coastlines . ...............74aDrainage - . ......69Hills and mountains -------- 60, 61Hydraulic structures ........120, 121Hydrology - . ......68Inland waterways - ....... 103Jungles -------------------- 49Landing areas -------------- 75Mines . . . . .. l..............109eNonurban areas . ...........130, 131Petroleum and gas ---------- 108Plains and plateaus --. . .....55, 56Quarries and pits ----------- 112Railways --............. 101Reefs . .....................74bRoads . ...................96Rock . . ...............81Soils -. ...................78a, 79Terrain . ...................52, 132Tunnels ................- 80cUrban areas . ...........123, 124Utilities . . .................128Vegetation - . .............90, 91Water supply . .............147Water terminals . ...........117, 118

Military pipelines . ..............106cMilitary use of railroads -------- 99fMines . . .......................109Mobility index . .................1741Models, terrain . ..............17Monsoon . . ....................27fMoss …............84cMountains -_-_-...........5-- - -- 7, 58,

140g

National Intelligence Survey ___20aNatural gas -. ................104Needleleaf forest . ..............85dNimbostratus clouds . ..........29h (2)Nipa palms -. ...............84bNonurban areas . ..............129Nuclear weapons . ..............37c, 78h

Page8593

8, 14232

66, 721444831866831323186

96116

7872

61, 63111

71993880

103lrT102

52, 6010598799584

82, 8545, 120

83113, 114

11789, 91

13010710197

102143

81685

60, 61,126

11100

871985

11726, 83

Paragraph Page

Observation and fields of fire --- 48d(2), 37, 39,49e(1), 41, 57,50d(1),55c 61,9060b, 90b, 113, 120,1236, 134, 138159a

Obstacles . ...................48d(4), 50f 37, 42,60d, 90d, 62, 90,136, 161, 121, 138,173d 143

Oil, military importance .........107 101Oil distribution . ................106 100Oil fields ....................- 105 100Oil pipelines . ..................106b 100Oil tanks . . ...................106e 101Open-pit mines . ................109¢ 103Orchards . ...................89b 89

Passes, mountain . ...........58e 61Peaks . . .......................57b 60Perennial stream - . ......... ..63aa 64Petroleum and natural gas ..... 104 100Photographs -. ........ ........18 9Pictomaps . ...................17a(5) 9Piedmont plains ----- . .........53g 49Pipelines, military oil . .......106 100Pits --------------------------. 111b 104Placer mines . ..................109b 103Plains ------------------------- 53, 55, 45, 52,

145b 129Planning . ......................132 120Plants ------------------------- 82 84Plateaus ….......54,55 50,52Polar climate …----…-----------45 33Polders . . ....................119e 110Ports . . .......................116 107Prairie .....................- 88c 89Precipitation . ...............30, 21,

1556(3) 135Pressure, atmospheric . ..........26 14Production of terrain intelligence _12 7

Quarriesl ----------------------- illa 104

Railways . ....................99, 100 96, 97Rain, tropical . ...............84a 85Rain forest . ...................441a 30Rainfall . .....................30, 39a 21, 26Ranges, mountain --------------- 57c 60Rating cone index . .........174g 143Reconnaissance reports ---------- 20f 11Reefs ....... . ..................73, 74 77, 78Relief . . ......................51c, 156a 44, 135Remolding index - . ............174f 143Remote-sensor imagery - ...... 18 9Reports, intelligence . ..........20 11Reserved route . ...............95c(3) 94Reservoirs . ..................119¢ 109Rice fields . ...................89c 89Ridge and stream lining ....... 156 135Ridge approach . ...........1396 126Rivers … ...---------------------63, 68 64, 71Rock ------------. . ............80 83

175


ParagraphRoutes and roads _______________95

Sample terrain study ___ ---_App. CSand _-______________________76cSand dunes ____________________48bSavanna -.---------- 88bSavanna climate .---------------41bScreening smokes ------------- 48d(7)Scrub, Mediterranean ---------- 85bSea approaches --- ___----------- 168Seeps and springs - …------ ___ 67c, 144bShrubs _…__ __-__________ 87Silt ________________ ___ 76dSlipperiness …........_____ ____ 174k,

176bSoils _______________________ 76, 78,

169, 1736,174, 175

Soil maps ._____.__________-___-17a(1), 77,172

Soil trafficability table ____…___175Soil-type symbols (table 2) .__-175aSpecial operations __________140Springs, artesian ____ .____-___'.7c(2)Springs, gravity _-___________ 67c(1)Springs and seeps __________-__67c, 144bSteppes _______ ______…__42c 88dStereopairs …_.___…________._ .18d(2)Stickiness, soil …_______… _____174j, 176aStorms _______-__________.___ 32Stratocumulus clouds _____…_…___29h(3)Stratus clouds -- ___ ___-____.___29h(1)Streams __- _6_______8_______63, 144c

Studies:Climatic ._________ .___App DTerrain __________-___.___App C

Subarctic regions ___________..___44e, 50Subtropical climate ___ .____..___43cSupervised route . ...........___..5c(4)Surf ________ …___________.___ 168eSwamp, tropical .-. __..____ 84bSwamps and marshes -- ___65, 68e

Temperature __ …_________.___835, 1556(2)Terrain …________________.___4, 6, 52,

114, 132,136d

Terrain models ____ …_._.______17Terrain studies ________________148,

App. C

7;

8

-1o

Page paragraph93 Thunderstorms .---------------3 2a

Tides _____-_________________ __168f153 Topography _ . .................51, 72, 122b

81 141c(4),36 171, 173a30 Tornadoes …_--.. .............. _.32b3038 Traction capacity of soils ........174d86 Trafficability . ...............169

141 Trees _…________._.______-___830, 129 Tropical climate _..___________41

88 Tropical cyclones ...--._________ 32cTropical grasslands _______.___._88bTropical rainy climates ________41

14,5 Tropical regions _- -.... _____ 490, 82, Tropical swamp . ...............84b

Tundra --. ....__________.__ 46Tunnels ............- _._.._._ 80c

143, 1408, 81,

1421451451267070

70, 12931, 89

10144, 145

221919

64, 129

161153

33, 403294

14185

66, 72

24, 1344, 45,

105, 120,122

8

Underground installations … _.____80bUnderwater topography _________72Urban areas .--------------_-- 122Utilities ________ ______________ 127

Page22

14144, 75,

112, 127,142, 143

22143142

843022893038853483

8375

112117

Valley approach -._-------------139a 123Valley wind .-------------------27c 16Valleys, kinds __…_.____________58b 61Vectographs . .................. .18d(2) 10Vegetation ..................... 82, 89, 84, 89,

156c 173 136, 143Vehicle categories (table 3) ……________________ 146Vehicle cone index __________174i, 177a 144, 145Velocity, wind (table 1) __. . .._.____._._____ 15Visibility __ _________155b(1) 134Volcanic lava _-____________ 53d 48

Water, sources and supply ______ 142, 143, 1146, 166 1

Water table _____-____________ 67bWater terminals ...- …-_…______ 116Waterways, inland .- ..._...102Weather …..............-24, 170Weather forecasts .--___________33, 34fWeather intelligence …______ … 34Weather requests ___…_________. 34dWells …___ _____________ 145eWind velocity (table 1) __________________.Winds ________-______________. 27, 36,

155b(4)132, World rainfall _ _____ ___30153 World temperature _____________40

27, 128,130, 139

6910798

13, 14222, 24

2324

130- 15

14, 251352128

176


By Order of the Secretary of the Army:

Official:KENNETH G. WICKHAM,Major General, United States Army,The Adjutant General.

HAROLD K. JOHNSON,General, United States Army,Chief of Staff.

Distribution:To be distributed in accordance with DA Form 12-11 requirements for terrain intelligence.

* U.S. GOVERNMENT PRINTING OFFICE: 1967-0 273-544


MOVEMENT MAP6020'15'

51°6'55'7-10`45'

2A -

51o6'55' Sample Movement Color Key

Specific Movement Key

Mountains and steep hills generally woodedTravel restricted to the few e xisting road--s ....Gently sloping and level land:; slopes lesstran 10/,sairdy or grave-1y soil; gOd movemeit in all but wort -ea t her .....

Gently sloping and level land: slopes lessthan l0 loamy or clayey soil; good move

1A

Gently Moping and evel Jand, urban areaTraffic retrite.d to wtreet . __2CWooded areas Densi ty, type and thicknessof trees giavn ocm ap and these factorsdetermine practicability of passage . . . ..

Drained swamps and flood plains: manycanals and ditches Dlsruption of canaldrainage causes flooding Generally untraffic.bl---- -- I-4AMine pits and spoil heaps Untraficablebecause of steep slopes and holes.E..

Swamps Impracticable .. . ........ 5

LEGEND

Woods... ; - -

Raliway. multiple track(with tunneI) ..__ . .....-

Landing strip, light aircraft ... /

Highway. autobahn, routeclass 40 ft X 65 T

Highway. primary, routeclass 20 ft. X 55 T . ...

Highway, state, routeclass 20 ft X 55 T . . ........

Bridge, railroad or highway T. ...- -

Stream .canal, and river .........

Airfield, arge municipal

Escarpment and mining pits

-0-----

50039,30o =6'20'15'

This sample movement map is not to scaleJJ 50*39'30'7'10'45 '

. 9.

2 mils ' . o r -

Ae o men sea S lne , to n 19_I _

ANNUAL MAGNETIC CHANGE'* ' enr W)

Scale I 100O000

O I _ 2 3 5 g M 2s

0ooo 0 000 2000 3000 40o0 50o0 6000 70o0 0OOO Mlarsloon O I00 2000 3000 4O0 5000 6000oo 7000 OOO0 yMrd

Contour Interval 50 FeetPrepared by The Engineer SChool, For Belvoir. 1959Map keyed to Germany 1: 00,000 AMS, SI and RI,1952. to which reference is made for marginal information Comments concerning field usability arerequested by The Department of Training Publications.The Engineer School, Fort Belvoir, irginia Fo illustrative purposes, bidge dolssfication infoematlon hasbeen purposely omitted from this map. Route csasifi -cation infogmation has been added to the legend under

dsFi e . Movement ap of Coloe aFigure 61. Movement Map of Cologne area.

1

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Railway, single track

COLOGNE AREA


RHINE PLAIN

The RHINE PLAIN consists of three related areas; (1) flood plains of the lowerROER, ERFT, and RHINE RIVERS; (2) the terraces along these rivers; (3) theprairie lands between the rivers.

Flood Plains

The flood plains of the ROER and ERFT RIVERS are quite flat and are dissec-ted by many ditches and drainage channels. They have complex soils of silts andvery fine sands; a high water table makes them difficult to traverse during wetperiods. Portions of the flood plains are drained swamps with considerable organic

material in the soil. Traffic is restricted to the road system by these factors,but foot troops will encounter only minor difficulty. The flood plain of the RHINERIVER is quite narrow, as the river terraces closely approach the river on thewest bank between BONN and COLOGNE. The RHINE RIVER here is 900-1400

feet wide, has a 2-4 ft/sec. velocity and is 20-40 feet in depth.

River Terraces

HOHE VENN HIGHLAND

The HOHE VENN HIGHLAND shown on the map is the northern tip of a muchlarger forested plateau to the southwest. It has two principal landforms . . . adissected upland and the upper ROER RIVER valley system.

River terraces are poorly developed along the ROER and ERFT RIVERS, butreach a grand scale along the RHINE RIVER where four or five terraces can befound. They are composed of sandy or occasionally loamy soil, and are up tofour miles wide along the west bank. Cross-country movement is good to excel-lent in most weather. Slopes between terraces are usually less than 10 percent,while the terraces themselves are practically level. One boggy spot (5) is shownbetween COLOGNE and BONN, but others, all of very small size, may be presenton the southwestern outskirts of COLOGNE. Terrace slopes along the BOER and

RHINE RIVERS are good sources for gravel aggregate.

Upland

This upland is made up of flattened sandstone hills 300-500 feet high withsteep wooded slopes usually above 25 percent. Bluffs are common. Some of theflattened hilltops are open and are used for farming and pasturage. Principal soiltype is loam. Cross-country movement is good in the open areas, but steep sand-stone-shouldered ravines are frequent barriers. Trails and roads provide occasionalpassage from the open hilltops through defiles to the lowland valleys. In thisarea, sandstone may be quarried. Towns are small and scattered, and constructionsites for facilities are limited. Road and rail communication is poor as comparedto the lowland plains.

Upper ROER RIVER Valley

Prairie Lands

These are extensive areas of very gently rolling topography mostly taken up withfarmland. The land between the ROER and ERFT RIVERS, and that north of theJULICH-COLOGNE highway are examples of prairie lands. Soils are sand loamto clay loam, rather thick, and are the weathered product of loess deposits. Sandyareas are found, and are due partly to glacial outwash, and partly to the lith-ology of the underlying rock. Cross-country movement over prairie land is goodin fair weather, but hampered by mud to a degree dependent upon the sand con-tent of the soil. Scattered wooded areas which usually possess soils of the sameloamy nature are delineated on the map. Prairie lands are well suited for mosttypes of military surface construction.

This valley system is rather narrow with steep wooded sides and occasionalescarpments. The valley floor does not exceed one-half mile in width but ismade up of sandy gravel; cross-country movement is good under most conditions.The ROER RIVER is approximately 80 feet wide in this vicinity, with a streamvelocity of 4-8 ft/sec. Two large dams several miles upstream control its flowand much of the valley floor may be flooded by release of the impounded water.Traffic into and out of the valley is restricted to roads, but a railroad followsthe river route into the city of DUREN.

VILLE RIDGE

GENERAL WEATHER-MOVEMENT RELATIONS

Although February and March are months low in total precipitation, weather con-ditions cause soil to retain a high moisture content. Alternate freezing at nightand thawing during the day prevents normal drainage. Freezing is seldom intenseenough or of such a duration to facilitate movement. The snow cover normallydoes not exceed six or seven inches at any one time, which will not hinder trackedvehicles but may necessitate the use of chains on wheeled vehicles. Good cross-country movement may be counted on for no more than eight or nine days permonth in the prairie lands during this period of the year.

The VILLE RIDGE is a long (25 miles), narrow (3-5 miles), southward risingpromontory with summits 100 to 250 feet above the surrounding countryside. Sur-face soil type is clay loam with sand loam along the flanks of the ridge, butthe overburden is rarely in sight due to extensive surface coal mining. The minepits, dumps, and spoil heaps, and the great number of industrial buildings effec-tively limit vehicular movement to roads. Scattered mixed and broadleaf forestsare found throughout the ridge and are indicated on the map. Crushed rock isavailable in the mine dumps. Several coal-driven power generating stations arelocated here. The ridge area is unfit for airfield sites because of mines, indus-trial towers, buildings, woods, and so on.


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Figure 71. Natural terrain features.


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Figure 7,1.--Continued


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Figure 71.-Continued


FM 30-10 ( Terrain Intelligence ) 1967 - Survival ebooks manuals/1967 US Army Vietnam War...CHAPTER...

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Transcript of FM 30-10 ( Terrain Intelligence ) 1967 - Survival ebooks manuals/1967 US Army Vietnam War...CHAPTER...