- Terrain appreciation is the evaluation of the area of probable military operations to determine the effect of the terrain on the lines of action open to opposing forces in the area. The purpose of this appendix is to describe the means of evaluating terrain and to show the effects of terrain on tactical dispositions.
- The character of the area or region of military operations often exercises a decisive influence upon the course of operations. The more important factors to be considered in evaluating terrain include not only natural features such as ridges, streams, bodies of water, woods, and open spaces but also man-made features such as roads, railways, and towns.
- Ground forms such as a succession of ridges and valleys may influence military operations by aiding or hampering the movement of military forces. An advance parallel to the ridges and valleys is mechanically easier than movement across successive ridges.
- The opportunity to utilize favorable terrain features may determine the salient features of the commander's plan of action.
- Terrain Factors.--No matter what the type of terrain and no matter what the tactical situation, terrain can always be evaluated in terms of the following five factors:
Fields of fire.
Concealment and cover.
- Observation of the ground on which a fight is taking place is essential in order to bring effective fire to bear upon the enemy. Observation also aids in increasing the effectiveness of fire directed on an enemy stopped by obstacles.
The value of cover and concealment is based on denial of observation to the enemy. Observation also affords information as to what the enemy and the commander's own troops are doing and makes it possible for the commander to control the operations of his own troops.
- Fields of fire are essential to the defense. An ideal field of fire for infantry is an open stretch of ground in which the enemy can be seen and in which he has to protection from fire as far as the limits of effective range of the infantry weapons. This is rarely realizable, and how nearly it can be approached depends primarily on the terrain. Fields of fire can be improved by cutting or burning weeds, grass, and crops; by clearing brush and trees; by demolishing buildings, and by cutting lanes through woods; but concealment must be considered in each instance. the time and labor available for such improvement should be considered in evaluating the terrain. On the offensive, infantry suffers when the defenders have good fields of fire and therefore finds such fields of fire disadvantageous.
- Concealment and cover.--Concealment from view both from the air and form the ground may afford cover only while the enemy does not know that the natural or artificial feature is occupied. Cover includes protection from fire, provided by accident of the terrain, or that provided by other natural or artificial means.
- Obstacles are obstructions to the movement of military forces. Some of the common natural obstacles of military value are mountains, rivers, streams, bodies of water, marshes, gullies, steep inclines, and heavily wooded terrain.
- Mountains which are parallel to the direction of advance of a force limit or prohibit lateral movement and protect the flanks; when perpendicular to the advance they are an obstacle to the attacker and an aid to the defender.
- Rivers are similar to mountains in their effect on forces moving parallel and perpendicular to them; in addition, rivers flowing parallel to the advance may be used as routes of supply.
- Marshes frequently provide more delay to an advance than bodies of water, because it is generally more difficult to build causeways than bridges. Mechanized vehicles can be
restricted in movement by dense woods, marshes, steep inclines, gullies, stumps, large rocks, and bodies of water 3 or more feet in depth.
- Communications (that is, roads, railroads, waterways, airways, and their facilities) are important to both offense and defense for the movements of troops and supplies. In some situations, especially in the operations of large bodies of troops, the means of communication are of vital importance.
- Objectives.--Terrain objectives, normally, are clearly defined features, the capture of which will insure the defeat of a hostile force, or form which the operations can be continued, or the success exploited. Terrain objectives, in the attack by ground forces, usually are located in or in rear of the hostile artillery area. One may be a terrain feature affording commanding observation, another a critical point in the hostile command system or an essential supply route, and another an obstacle to armored forces. In some situations, the objective is clearly indicated by the mission; in others it is deduced form the situation.
- Maps and Reconnaissance.--Maps are the basis for terrain studies but should be checked by air reconnaissance, air photographs, and ground reconnaissance. Works of man, especially routes of communications, are changing constantly, and even natural ground forms may change.
- Classification of Terrain Terms.--
- Features such as ridges, streams, woods, roads and towns divide practically all terrain into more or less separate areas. Such an area frequently consists of a valley lying between two ridges or an open space between two wooded areas. When the terrain features inclosing the area prevent direct fire and ground observation in to the area from positions outside, the area is called a "compartment." The location, size, and shape of a terrain compartment determine its suitability for tactical use by a unit of a given size.
- Terrain compartments are classified in accordance with the direction of the longer dimension in relation to the unit utilizing the terrain. Thus, a compartment whose longer axis extends in the direction of movement of a force or
leads toward or into a position is called a "corridor"; while compartments extending across or oblique to the direction of movement of the force or its front are designated as cross or later, or oblique compartments (corridors).
- Terrain compartments may be of any size or shape. They may be simple or complex, with the interior subdivided into smaller compartments. The limiting features at the edges may be high or low, continuous or discontinuous; a compartment may be inclosed on only two sides or on all sides.
- Influence of Corridors on Attack.--
- In general, a corridor factors the attack because it limits the lateral organization of the defender's fire. Troops attacking within a corridor are afforded some defilade form hostile small arms located outside it. The features bounding it limit ground observation. This is of special importance since it reduces the effectiveness of hostile artillery fire. While a unit advancing or attacking along a ridge is subject to direct observation and fire form the enemy's troops that are located on either side of the ridge, a unit advancing or attacking in a corridor is subject to direct observation and fire only from that corridor. The attacker can concentrate his attention and fire power upon the neutralization of this hostile direct fire and ground observation.
- It may be concluded that a corridor leading toward or penetrating the enemy's position usually implies a combination of terrain factors favorable to the attack, in that it affords and avenue of approach and facilitates infiltration and penetration. The attacker, therefore, seeks to utilize corridors wherever they exist.
- Where terrain is the decisive factor, boundaries between tactical units in the attack should coincide with the boundaries of corridors. The reasons for this fundamental are as follows:
- When a subordinate commander is given a mission, he receives a responsibility which includes the full authority to control a given area. This area is designated by boundaries which should be located on the ground so that there is no misunderstanding as to the division of authority.
- In the attack, the ridges on each side of a valley corridor afford essential observation. Accordingly, the boundaries of areas of responsibility naturally fall along the crest of the ridges on the sides of the corridor. (See fig. 1.) If woods form one of the limiting features, the zones of action should include that portion of the margin of the woods from which the enemy can observe and fire directly into the corridor.
Figure 1.--Boundaries in attack.
- Influence of Corridors on Defense.--
- In the defense, boundaries are usually located within corridors.
- The defense is built around a series of tactical localities the retention of which will insure the integrity of the position. These localities generally include the high ground which affords observation and command of the attacker's approach. One subordinate commander should be responsible for each front line locality. Since these localities usually include the high ground for observation, the boundaries are located between the higher places, i.e., within corridors. A
boundary is usually placed along the slope of one of the ridges inclosing a valley. (See fig. 2.). Similarly, it is preferable to avoid placing a boundary within a woods or village.
Figure 2.--Boundaries in defense.
- At longer ranges to the front, however, boundaries are intended primarily to coordinate artillery fire, and will be influenced by the location of possible hostile assembly areas and routes of approach. Due to these factors and others at the longer ranges, boundaries which indicate sectors in front of the defensive position frequently are placed along the crest of a ridge. (See fig. 3.).
- The extension of the boundaries to the rear either in attack or defense is influenced largely by the location of roads which are needed for the movement of supplies.
- Influence of Cross Compartments (Cross Corridors) on Attack and Defense.--
- General.--Observation and fields of fire are practically continuous across the front throughout the length of most cross compartments. This is a distinct advantage to the defender for it permits him to concentrate artillery and small arms fires upon various parts of the front without changing observation posts. It also favors
the development of a system of crossed flanking fires. In attacking a defensive position which has utilized a cross compartment, the attacker must neutralize a relatively wide front which usually has no definite limits on the flanks. Thus an attacking unit usually cannot neutralize all of the fires bearing upon it but must depend upon adjacent units for assistance. Responsibility becomes less clear-cut, and more dependence must be placed upon cooperation between adjacent units.
Figure 3.--Boundary in defense; adjustment to terrain at longer small arms ranges.
NOTE.--Broken line indicates normal locations of a regimental boundary; corresponding solid line indicates adjusted boundary.
- Observation and field of fire.--The forward limit of a cross compartment is also the limit of the defender's observation and fields of fire. the attacker's observation and fields of fire are limited by the terrain feature which closes the cross compartment on the defender's side. Therefore, as far as the effect of the attacker's weapons is concerned, his attack is well-supported until it reaches that terrain feature, but the support thereafter suffers a material reduction
in effectiveness until such time as the artillery observation and infantry supporting weapons can be moved forward to command the next succeeding terrain feature. Successive cross compartments in rear of the initial position afford the defender observation and fields of fire for successive defensive positions.
- Concealment and cover.--The limiting terrain feature on the defender's side of a cross compartment affords cover for his troops. He is able to maneuver his reserves and to maintain his rear installations with relative safety from ground operations until the attacker passes beyond this terrain feature. The attacker also is afforded cover for his initial dispositions by the limiting feature on his side of the cross compartment, but as the attacker crosses the crest of the ridge and emerges from the forward limits of the cover afforded by this feature, his forces become exposed to hostile observation and fire.
- Obstacles.--In the valley cross compartment, the main stream is located across the direction of advance of the attacker. Its influence as an obstacle constitutes one of the advantages of the cross compartment to the defense, particularly where the obstacle can be covered by observed fires.
- Aids to Study of Terrain.--
- Drainage lines and ridge lines form the natural basis for the study of terrain with respect to the shape of the ground. When such study of ground forms is made on a map or aerial photograph, it can be aided materially by--
- Emphasizing the drainage lines by marking them heavily.
- Drawing in heavy lines along the crests of ridges, called "ridge lining."
- On contoured maps, emphasizing certain contours with heavy lines or coloring the map areas between selected contours with a separate tint or color for each range or elevation in order to make the ground forms and commanding elevations more apparent.
- Drainage lines always form a connected system or systems of branching lines. ridge lines form similar systems of branching lines, since spurs and the smaller ridges branch off from large main ridges just as small streams and gullies
branch off from the main stream. Drainage lines and ridge lines thus form two interlocking branching systems which, either singly or together, indicate clearly the general shape of the ground. When both systems are emphasized on a map or photo, different colors should be used; preferably blue for drainage lines and brown for ridge lines to conform to the usual map colors. The more important ridge or drainage lines can be given special emphasis by drawing them in with heavier lines.
- It will frequently occur that ridge lines and drainage systems are not the only terrain features of outstanding importance in a tactical situation. There may be forests, towns, railroads, etc., to which particular attention must be paid. In such cases, these features can be emphasized in much the same ways as described above for ridge lines and drainage systems.
- Tactical Study of the Terrain.--
- Purpose.--An appreciation of the terrain is an important element in every tactical operation. Its tactical study may be mental, oral, or written, depending upon circumstances. It may be made by the commander himself, or by any subordinate designated by him. Form 4, page 94, is designed as an aid to the systematic study of terrain.
- Limiting considerations.--The study of the terrain should comprise all of the area involved in the contemplated operation. The details of the study are affected by other considerations. A commander making a tactical study of the terrain is limited by his mission and his own and the enemy capabilities. G-3 in preparing details of a tactical study of the terrain is limited yb the capabilities of his own force and by the commander's decision or directive for the operation; G-2 is usually limited by the enemy capabilities. The specialist, such as the tank commander, the artillery commander, the chemical officer, or the engineer, will find his study limited by the powers and limitations of his arm or service.
- General topography.--Any deductions made as to the tactical effects of the terrain must be based upon a knowledge of the topographical features of the area under consideration. The following should usually be considered:
- Drainage system.--Streams and valleys are of particular importance because, together with the intervening ridges, they constitute the general framework of the terrain.
- Ridge system--This is the complement of the drainage system discussed above and should be approached in the same manner.
- Routes of communication.--The road net available for tactical maneuver or for supply; the presence or absence of rail facilities, navigable waters, and airplane landing facilities all come under this subhead.
- General nature of the terrain.--All the foregoing information is briefly summarized in a final paragraph.
- Military aspects of the terrain.--Having stated the facts upon which further conclusions are based, the study now proceeds to the evaluation and interpretation of these from the military point of view. Here the study may assume the aspect of an intelligence study, of an operations study, or of both. As a means of systematization, the area is divided for purposes of discussion into natural subareas; or if there are no distinctive natural boundaries into subareas delimited with regard to the tactical situation. Within each subarea, terrain elements which affect the military situation are considered; where applicable, each element is considered both from the enemy's viewpoint and from our own.
- Critical terrain features.--As a result of the above study it frequently happens that a certain terrain feature, for example a dominant hill or ridge, or an obstacle to mechanized attack, becomes critical in the contemplated operation, so that its possession by either the enemy or boy our own forces will have a marked influence upon the operations of either side. If there is such a terrain feature it should be briefly discussed at this point. If there is not, a statement to that effect should be made.
- Tactical effect of the terrain.--This portion of the study should summarize the effect of the terrain on the immediate tactical or administrative situation. Using the systematic method of approach, it will in many cases be desirable to discuss each ene y capability separately, from the viewpoint of the effect of the terrain upon it, and then to discuss in a similar manner each line of action contemplated by our own troops.
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