MCS 3-2 TERRAIN APPRECIATION (NAVMC— 3789) N1PM1IIW1/ 1945 Published : — For Instructional Purposes Only. MARINE* CORPS SCHOOLS MARINE BARRACKS, QUANTICO, VIRGINIA MARINE CORPS SCHOOLS MARINE BARRACKS, QUANTICO, VIRGINIA "Terrain Appreciation" is approved and published for instructional purposes in the Marine Corps Schools. W. H. RUPERTUS, Major General, USMC, Commandant. TABLE OF CONTENTS SECTION 1 IMPORTANCE OF TERRAIN APPRECIATION General Paragraph 1 Page 1 Influence of Terrain - ...... - 2 1 SECTION 2 TERRAIN FACTORS General _ - 3 3 Observation - 4 3 Fields of Fire 5 3 Concealment and Cover Obstacles 6 7 3 4 Communications 8 4 SECTION 3 TERRAIN COMPARTMENTS General 9 5 Simplest Form of Terrain Compartments 10 5 Significance of Terrain Compartments 11 5 Corridors and Cross Compartments 12 8 SECTION 4 INFLUENCE OF TERRAIN COMPARTMENTS ON TACTICAL OPERATIONS Influence of Compartments in the Advance Influence of Compartments in the Defense Combination of Corridors and Cross Compartments 13 9 14 9 15 10 SECTION 5 INFLUENCE OF TERRAIN COMPARTMENTS IN THE ASSIGNMENT OF BOUNDARIES Paragraph Page General - 16 13 Boundaries Along Corridors in the Attack 17 13 Boundaries Along Corridors in the Defense 18 16 Boundaries in Villages and Woods 19 20 Influence of Corridors on Boundaries Extending For- ward of the Defensive Position 20 22 Influence of Cross Compartments on Boundaries 21 23 SECTION 6 TACTICAL STUDY OF TERRAIN Purp o s e 2 2 Factors to be Considered 23 Aids to Study 24 Methods of Marking a Map or Aerial Photograph 25 Form for Estimate of the Terrain . 26 25 25 26 27 36 LIST OF ILLUSTRATIONS Figure Page Terrain Compartments 1 6 Terrain Compartments in the Advance 2 7 Terrain Corridors 3 10 Absence of Terrain Corridors 4 11 Combination of Corridors and Cross Compartments 5 12 Boundaries in the Attack - 6 14 Boundaries in the Attack 7 15 Boundaries in the Defense 8 17 Boundaries in the Defense 9 18 Boundaries in the Defense 10 18 Boundaries in the Defense 11 20 Boundaries Through Villages and Woods 12 21 Boundaries Avoiding Villages and Woods 13 21 Extension of Boundaries in the Defense 14 22 Section of Contoured Map 15 27 Drainage Lines Emphasized 16 28 Ridge Lines Emphasized 17 29 Drainage and Ridge Lines Emphasized 18 30 Emphasizing Contour Lines 19 31 Emphasizing Roads 20 32 Emphasizing Railroads 21 33 Unmarked Aerial Photographs 22 34 Marking Aerial Photographs 23 35 ii INTRODUCTION The study and evaluation of terrain with a view to its use for military operations is one of the most important things leaders of all units must know. History is replete with examples of success in battle due to the careful study and use of terrain, and is just as replete with accounts of battles lost because commanders failed to appreciate the terrain. More often than not troop formations, positions to be defended, and locations of weapons are dictated by the ground and these solutions must be read from the ground. It must be remembered that in evaluating terrain, as in everything else dealing with military operations, there are no rules but there are established principles which, when applied intelligently to a given situation, will bring forth a sound solution. Knowledge and application of these principles alone are not sufficient but they must be so thoroughly under- stood that they may be intelligently violated if necessary. SECTION 1 IMPORTANCE OF TERRAIN APPRECIATION 1. General. — a. 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 text is to describe the means of evaluating terrain and to show the effects of ter- rain on tactical dispositions. b. No commander can afford to neglect any of the fac- tors that may lead to the success of his undertaking, and it must be understood that terrain is one of the most important of these factors. Commanders must understand the influence of terrain features upon military operations, for no tactical situation can be properly analyzed without a sound knowledge of terrain. c. The importance of a thorough comprehension and analysis of the terrain over which an operation is to take place is clearly stressed by Captain Ralph Ingersoll in his book "The Battle Is the Payoff." He says: "The study and intimate know- ledge of terrain is the beginning and end of tactics. Every- thing to do with the ground, its shape, its contours, its texture, even its color at different hours of the day affects everything both you and the enemy do and can do. The two adver- saries have the terrain of the battlefield in common. Other things being anywhere near equal, the victory will go to which- ever understands the terrain best." d. The ability to appraise a piece of ground in the light of its tactical importance should be constantly developed by every leader from the highest commander down to the squad leader. It is just as essential for a squad leader to evaluate, or appreciate, the terrain over which his squad will operate as it is for a corps commander to evaluate the terrain over which the corps will operate. 2. Influence of Terrain. — a. The character of the area or region of military operations often exercises a decisive influ- ence upon the course of operations. The more important fac- tors 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. b. Ground forms such as a succession of ridges and valleys may influence military operations by aiding or hamp- ering the movement of military forces. An advance parallel to the ridge and valleys is mechanically easier than movement across successive ridges. c. The opportunity to use favorable terrain features may be a major influence in a commander's plan in either attack or defense. In the former, terrain may dictate the objec- tive, the formation, and scheme of maneuver ; in the latter, it will affect the choice of positions to be occupied and the dis- positions made upon them. SECTION 2 TERRAIN FACTORS 3. General. — No matter what the type of terrain and no matter what the tactical situation, terrain must always be evaluated in terms of the following five factors : Observation. Fields of fire. Concealment and cover. Obstacles. Communications. 4. Observation. — Observation of the battlefield is essential in order to bring effective fire to bear upon the enemy, to con- trol the maneuver of one's own troops, and to prevent surprise by the enemy. It is obtained from commanding elevations and from the air. Command and fire control are to a great measure limited by ground observation. Commanding elevations, there- fore, are important because they afford extensive observation of the surrounding terrain. Observation is not only important in itself, but it enters largely into the influence of the four other major factors — fields of fire, concealment, obstacles, and communication — by which terrain features may be evaluated. 5. Fields of fire are based on observation since the infantry soldier or artillery observer must be able to see his target in order to bring effective fire to bear upon it. Next to observa- tion a suitable field of fire is the most essential factor in the selection of a defensive position. 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 no 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 caution must be exercised in each instance since obviously constructed fire lanes might disclose the location of positions to an ob- servant enemy. On the offensive, infantry suffers when the defenders have good fields of fire ; consequently, commanders of all units must be constantly on the alert to recognize ter- rain affording long fields of fire so that such terrain may be avoided or other measures taken to minimize its effectiveness. 6. Concealment and cover also emphasize the value of ob- servation. Concealment implies the denial of observation to the enemy both from the ground and from the air and may 3 often be obtained by a proper evaluation and use of the ter- rain alone. At other times artificial means in addition to a sound use of the terrain are necessary in order to provide adequate concealment. Concealment is a complement to cover only as long as the enemy cannot determine that a terrain feature is occupied. Cover includes the protection from fire afforded by accidents of the terrain. 7. 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. a. 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. b. 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. c. Marshes frequently provide more delay to an ad- vance than bodies of water because it is generally more diffi- cult to build causeways than bridges. Mechanized vehicles can be restricted in movement by dense wood, marshes, steep in- clines, gullies, stumps, large rocks, and bodies of water three or more feet in depth. 8. Communications (roads, railroads, waterways, airways, and their facilities) are important to both offense and defense for the movement of troops and supplies. In some situations, especially in the operations of large bodies of troops, the means of communication are of vital importance. In combat the facility with which routes of communi- cation of all kinds can be used depends upon the extent to which the enemy may be denied observation of them. Thus, a study of terrain necessitates an evaluation of the effect of terrain on observation, fields of fire, concealment and cover, obstacles, and routes of communication, with obser- vation being the key to all. SECTION 3 TERRAIN COMPARTMENTS 9. General. — a. All of the five factors which have been considered in relation to terrain are derived from one great quality of terrain — "relief." Relief is the division of the earth's surface into alternate areas of elevation and depression. It is the third dimension of the ground and divides the terrain into features such as hills, valleys, plains, ridges, and other ground forms. b. These features, or ground forms, appear in an infinite number of combinations and divide all terrain into separate areas of varying sizes and shapes. When an area is enclosed on at least two sides by terrain features that prevent observation and direct fire into the area from a point outside, the area is called a "terrain compartment/' Its location, size, and shape determine its suitability for tactical use by the par- ticular unit concerned. 10. Simplest Form of Terrain Compartments. — a. A ter- rain compartment in its simplest form usually consists of an area of low relief, such as a valley or ravine, enclosed on two or more sides by ridges or high ground, or other terrain features, natural or artificial, which deny observation and direct fire into the compartment from any position outside the limiting terrain features. A terrain compartment consisting of a single area of low relief enclosed on two or more sides by limiting terrain features is known as a simple terrain com- partment. A terrain compartment, the interior of which is subdivided into smaller compartments, is known as a complex compartment. b. In figure 1 two simple terrain compartments are to be found. One is formed by the ridges GHI and DEF enclosing the ravine LM. These two ridges would prevent observation into the ravine LM from any point outside of the area GIFD. Similar in nature and characteristics to the compartment GIFD is the compartment DFCA formed by ridges DEF and ABC, which would prohibit direct fire and observation into the ravine JK from a point outside the compartment thus formed. 11. Significance of Terrain Compartments. — a. While the division of the terrain into compartments is based upon obser- vation, the real significance of the compartments is that from points outside of their boundaries, direct or observed fire can- not be brought to bear upon forces within the compartments. b. For example, the machine gun located at N in figure 1 would not be able to interfere with a force moving up through the ravine KJ since its fire is masked by the ridge Figure 2. — Terrain Compartments in the Advance. 7 DEF. Similarly an artillery observer at would not be able to bring observed fire to bear on a force moving up through the ravine ML since his observation is masked by the ridge DEF. 12. Corridors and Cross Compartments. — a. General. — Terrain compartments are classified in accordance with the direction of the longer dimension in relation to the unit utiliz- ing the terrain. Thus, a compartment whose longer axis ex- tends 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 lateral, or oblique compartments (corridors). b. Cross compartments. — In figure 2, assume that a force is marching from A toward B. The road crosses the three ridges CD, EF, and GH, which form the terrain compartments CDFE and EFHG. These are cross compartments since the direction of movement of the force is perpendicular to the long axis of the terrain compartment. c. Corridors. — If, however, the force is marching from R to S, it passes between the ridges EF and GH which form the sides of the compartment EFHG ; hence, in this case it is a corridor, inasmuch as the long axis of the terrain compart- ment extends in the direction of movement. SECTION 4 INFLUENCE OF TERRAIN COMPARTMENTS ON TACTICAL OPERATIONS 13. Influence of Compartments in the Advance. — a. In general, a corridor favors the attack because it limits the lat- eral organization of the defender's fire. Troops attacking within a corridor are afforded some defilade from hostile small arms located outside it. The features bounding it limit ground ob- servation. 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 from the enemy's troops that are located on either side of the ridge, a unit advancing or attacking in a corridor is sub- ject to direct observation and fire only from that corridor. The attacker need concentrate his attention and fire power only on the neutralization of hostile fire power and observa- tion within the corridor. b. It may be concluded that a corridor leading toward or penetrating the enemy's position usually implies a combina- tion of terrain factors favorable to the attack in that it affords an avenue of approach and facilitates infiltration and penetra- tion. The attacker, therefore, seeks to utilize corridors wher- ever they exist. 14. Influence of Compartments in the Defense. — a. To show the influence of terrain compartments in the defense, two illustrations are presented as the basis for study and compari- son. Figure 3 shows two well-defined terrain corridors, ABDC and CDFE. Figure 4, in marked contrast, represents a uniform slope from the line ACE toward the line BDF. b. Comparing the effectiveness of defensive fires in the two cases, it can be seen that in figure 3 only those weapons located within the corridor ABDC can fire on troops advancing up that corridor. Relatively, a similar situation applies to cor- ridor CDFE. Within each corridor, the defensive fire may be organized for mutual support in case of need, but the defense in either corridor cannot support the defense in the other cor- ridor by shifting its fires since the ridge CD prohibits the exchange of direct fires. c. In figure 4, where there are no corridors, all the defensive fires within the area ABFE can be organized for mutual support; these fires can be concentrated if necessary against a major threat anywhere within the area without the necessity of shifting observation posts. d. The backbone of a defense is the organized fire of automatic weapons, supplemented by observed artillery fires. As will appear from a comparison of figures 3 and 4, the de- fender can get more effective fires on terrain similar to that shown in figure 4. Since the terrain in figure 4 really forms one side of a cross compartment, the general statement may be made that the cross compartment is a terrain feature that favors the defense and handicaps the attack. This does not mean, however, that a cross compartment gives the defender a superiority over the attacker. It merely means that it gives the defender an advantage that he would not have if there were no cross compartment present. e. To an attacker, figure 3 would present the most fav- orable terrain since his advance in one corridor would not be interrupted by fires from another corridor, whereas in attack- ing a cross compartment as in figure 4, the attacker must neu- tralize a relatively wide front which normally has no definite limits on its flanks. The attacker must depend on other units for assistance in this case. This comparison leads to the gen- eral statement that the terrain corridor favors the attack. The attacker would therefore seek to use corridors if they existed since they facilitate the approach, infiltration, and penetration, while the defender would avoid them since they tend to weaken his defense by decreasing the flexibility of his fires. 15. Combination of Corridors and Cross Compartments. — a. Seldom will one side enjoy all the advantages afforded by the terrain. The defender seeks but seldom finds an ideal Figure 3. — Terrain Corridors. 10 condition such as illustrated in figure 4. The attacker studies the terrain for existing corridors but seldom finds a series of them such as shown in figure 3. b. More characteristic of the terrain usually encount- ered in the field is that represented in figure 5 where both corridors and cross compartments form a part of the general area pictured. A main ridge, the top of which is along the line AB, is cut by the gullies IJ, KL, and MN, bounded by spurs CD, EF, and GH. These spurs, since they parallel the direction of attack, form the boundaries of two terrain corridors, CDFE and EFHG. These corridors end at about the line CM. Above that line, the defender can organize his fires for mutual sup- port across the entire area ACMB, which is a cross compart- ment; below the line CM he is limited in the lateral organiza- tion of his fires by reason of the existence of the terrain corridors CDFE and EFHG. Figure 4. — Absence of Terrain Corridors. 11 Figure 5. — Combination of Corridors and Cross Compartments. 12 SECTION 5 INFLUENCE OF TERRAIN COMPARTMENTS IN THE ASSIGNMENT OF BOUNDARIES 16. General. — a. Probably one of the most important con- siderations in a commander's plan of action is the assignment of boundaries which define the limits of responsibility and authority of subordinate commanders. (1) Boundaries between units are considered sources of weakness in military operations since they always result in a division of responsibility. This results from the fact that small units engaged along boundaries do not have a common immediate superior whereas interior units do. (2) Since boundaries are sources of weakness, an attempt is made to place them so that the terrain will compen- sate to some extent for this division of responsibility. b. The discussion to follow deals with the considera- tions to be given by a commander in the assignment of boun- daries as influenced by terrain features. It must be borne in mind that other factors in addition to terrain almost always exert some influence in placing boundaries. 17. Boundaries Along Corridors in the Attack. — a. It has been shown that the existence of terrain corridors gives an attacker an advantage that he would not have in their absence. These corridors also affect the location of boundaries between units in the attack. b. Figures 6 and 7 represent identical terrain — the two corridors HKH and ILMJ, each of which, for purposes of this text, shall be considered suitable in width for a regiment in attack. Two methods of locating the boundaries between regi- ments are shown. In figure 7 the boundaries are placed at the edges of the terrain corridors while in figure 6 they are placed within the corridors (along the center). The boundaries could be drawn anywhere between these two extremes but these locations will serve as general examples since, as will appear later, the choice is really between that shown in figure 7 and any other location. (1) Start with figure 6 and consider x the center regiment, the 6th Marines. This regiment has found it possible to overcome the defensive fires within its own zone of action and has made better progress than its neighbors. The attack has reached the position shown by the dotted line near the center of the figure. As the attack spearhead near D appears to be the major threat, machine guns on the slope BC and along the edge of the woods between F and J begin firing on the flanks of the 6th Marines ; an artillery observer on the slope to the right of H places fire on the left flank of the 6th 13 Marines. Thus the attacking troops are receiving fire not only from enemy units within their zone of advance but are also being hit by flanking fires from units outside of their zone. The attacker is at a decided disadvantage since he cannot mass his fires on any given spot due to the ridge IL which splits his zone of action. Likewise, he cannot place fires outside his zone without the necessity of coordination with adjacent units. If he does fire outside his zone, he thereby diminishes the amount of fire he has available to overcome resistance within his zone of advance. (a) The adjacent units will try to aid the advance of the 6th Marines in every way possible, but if one of them succeeds in pushing forward, the enemy can shift its fires to meet the new threat. Cooperation between adjacent units is essential, but one unit should not be dependent on adjacent units for the success of its advance. In this case the boundaries are so placed that the advantage ordinarily given to the attacker by the presence of terrain corridors is thrown away. (2) A study of figure 7 will indicate the potential progress of the 6th Marines when the boundaries of its zone of action are located at the edges of the terrain corridor HKLI. The 6th Marines has again been able to overcome the defen- sive fires in its own zone and its advance has become a serious mm ■r>r\r,' Figure 6. — Boundaries in the Attack. 14 threat to the enemy. However, the situation now differs mater- ially from that shown in figure 6. Because of the fact that the boundaries of the zone of action of the 6th Marines coincide with the boundaries of the terrain corridor HKLI, the defense cannot use any direct or observed fire from outside the corri- dor against the 6th Marines. As long as the 6th Marines can continue to overcome the defensive fires within its own zone of action, that is, within its own terrain corridor, it can con- tinue to advance. It can also materially aid the advance of its neighbors by flanking attacks to right and left from positions on the ridges bounding its zone of action. c. It is apparent that the attacker will have a better chance of success with boundaries located as in figure 7 than he would have with boundaries located as in figure 6. In figure 7 the influence of the terrain is appreciated and its advantage utilized; in figure 6 much of the advantage that might be gained by proper use of the terrain is thrown away by the improper location of boundaries. d. Where terrain is the decisive factor, boundaries between tactical units in the attack should coincide with the boundaries of terrain corridors. The fact that in some situa- tions this principle might have to be compromised by factors other than terrain does not affect the general truth of this statement. Figure 7. — Boundaries in the Attack. 15 e. Such a compromise might be necessary in the assignment of boundaries to a unit commander extending his zone of responsibility beyond the edges of a terrain corridor to avoid splitting a tactical locality or key terrain feature between two commanders. 18. Boundaries Along Corridors in the Defense. — a. Gen- era] principles governing organization for defense. — Terrain is only one of the factors that are considered in making plans for the organization of the ground. Where terrain corridors exist, however, terrain is a very important factor in determining the location of the boundaries between units and the strength with which different parts of the defensive position will be held. (1) The defense consists of a series of organized tactical localities, each prepared for all-around defense and the retention of which will insure the integrity of the position. The lateral intervals should be short enough to permit these localities to be mutually supporting. The primary terrain fac- tors — observation and fields of fire — often make it desirable that high points within the defense area be strongly organized for all-around defense ; the intervals between the high points are defended by flanking fire from the organized localities on the high ground and by the organization of other tactical localities echeloned to the rear. (2) The question of the establishment of bound- aries between units is an important one since these boundaries serve to allocate responsibility among the unit commanders concerned. The influence of terrain upon the assignment of these boundaries in the defense will be discussed in connec- tion with figures 8, 9, 10, and 11, which show identical terrain with three different methods of assigning boundaries. b. Boundaries along edges of terrain corridors. — (1) In figure 8 these boundaries pass through the high points A and B which will be well organized. Unity of effort requires that each such locality be placed under a single commander. Two commanders, each defending half of the ridge OB, can- not act as effectively as one commander who directs the defense of the whole ridge. The same applies to the ridges at A and C. Boundaries should, therefore, not be drawn as they are in figure 8. (2) It is true that the valley between A and B, which is a probable avenue of approach for the attacker, is entirely under the control of the commander of the 1st Bat- talion. His main reliance for defense, however, is not upon the head-on opposition that he can offer to the attacker's approaches up the valley, but in the continued possession of the organized localities at A and B. But the commander of the 1st Battalion controls only half of A and half of B ; there- fore, he has portions of two key points to defend rather than a single key locality. In the event the enemy succeeds in pene- trating up the valley the commander is faced with the problem 16 Figure 8. — Boundaries in the Defense. of trying to control the defense of two important localities separated by a hostile force. In order to hold his half of each of these tactical localities he must depend on the cooperation and support of adjacent commanders. The boundaries in this case are placed so as to weaken the key points of the defense — the points which must be held if the defense is to accomplish its mission. c. Boundaries along the lines of probable enemy pene- tration. — A more satisfactory method of boundary line assignment appears in figure 9. Here the key localities, namely, the ridges at A and B, are placed under the control of a single commander by establishing boundaries in the stream beds, that is, along the lines that the attacker will probably seek to penetrate. In this manner one source of weakness has been eliminated — namely, the division of responsibility for maintaining possession of the high ground. But in so doing another source of weakness has been introduced. The valley is the probable route of approach of the attacker; he will seek to penetrate the valley and then reduce the high ground by flanking attacks. By putting the boundaries in the valleys, responsibility for stopping the enemy advance up the valleys has been divided between adjacent commanders. 17 Figure 9. — Boundaries in the Defense. Figure 10. — Boundaries in the Defense. 18 d. Boundaries following neither the edges of the ter- rain corridors nor the lines of probable penetration by the attack. — (1) It now appears that neither in figure 8 nor figure 9 has the terrain been used to the best advantage. In both figure 8 and figure 9 the terrain offered the defense a real advantage, namely, high ground at A, B, and C. In figure 8 this advantage was neglected by dividing responsibility for retaining possession of these important terrain features be- tween two commanders. In figure 9 this mistake was avoided, but another was made in that the responsibility for stopping a hostile advance up the corridor XY is split between two com- manders. (2) There is a way of avoiding both of these mis- takes. In figure 10 the boundaries are drawn neither along the ridges nor along the stream beds but somewhere between the two. The commander of the 1st Battalion in this case has full control of the forces that will hold the ridge at B and oppose the advance of the enemy up the valley between A and B. Cooperation will still be necessary. He will expect to receive assistance from the battalions on his right and left. But the boundaries along which this cooperation must be arranged do not in this case pass through either of the two important ter- rain features which are the ridge and the valley adjoining it. A boundary line is always a line of weakness ; but by drawing the boundaries as they are shown in figure 10, this weakness is much less serious to the defense than it is if the boundaries are drawn as shown in figures 8 and 9. (a) As a general principle it can be said that from the standpoint of the most advantageous use of the ter- rain, boundaries in defense should neither follow the edges of terrain corridors nor the lines of probable enemy approach, but should be situated somewhere between the two so as to insure unity of command in holding key points and covering likely avenues of approach. (3) In studying the terrain represented in figure 11, an alternative arrangement of boundaries appears that seems at first glance to be as satisfactory as that shown in figure 10. Establishing the boundaries as in figure 11 conforms to the general principle just discussed since the boundaries shown divide neither the ridges nor the valleys between two commanders. The wooded valley between A and B, however, is more of a threat to the 2d Battalion in figure 11 than it is to the 1st Battalion. It offers an opportunity for the attacker to advance up the valley by using the woods for cover, capture the woods on the top of the ridge near 0, and capture the entire ridge from to B by attacking downhill from the rear. The commander of the 2d Battalion, therefore, has a greater interest in the defense of this approach and its defense should 19 Figure 11. — Boundaries in the Defense. consequently be assigned to him by drawing the boundary between battalions on the left of the wooded valley as shown by the broken line. It must be borne in mind that this discussion of placing boundaries in the defense is based upon terrain and that ter- rain is only one of the factors to be considered by the defender in assigning boundaries. Under the conditions shown in figure 10, the terrain factor has great influence since the terrain cor- ridors are well defined. If the terrain were flatter and the terrain corridors not so well defined, the terrain factor would not have so much influence; other factors in the situation might outweigh it to such an extent that the commander's decision as to boundaries might not conform to that shown in figure 10. 19. Boundaries in Villages and Woods. — The same principles apply when the boundaries of the terrain compartments are formed by villages or woods instead of by ridges. In figures 12 and 13 the village and woods usually are important features of the terrain. Responsibility for their defense should, therefore, not be divided as is shown by heavy lines in figure 12, but should be placed under a single commander as shown in figure 13. This is in direct contrast with the attack. An attacker would probably locate his boundaries as shown by the dotted 20 $mmm$$M* / "WKf Figure 12. — Boundaries Through Villages and Woods. ' / 111 o O < J JKfi- c o o