Figure 3-3a Secure Key Objective
Defense
Defensive operations on urbanized terrain are conducted in accordance with the fundamentals and principles contained in FM 100-5, Operations, and the How-to-Fight series of manuals. The general characteristics of the urban environment described in chapter 1 and appendix A influence the conduct of the defense at each command level.
This chapter supplements other doctrinal manuals by describing how the enemy may attack on urbanized terrain and how the defense is planned, organized, and conducted.
This section supplements the threat offensive doctrine sections of other How-to-Fight manuals by describing how the enemy may attack built-up areas on the urbanized battlefield. It also discusses his organization for combat and use of the combined arms team in this environment.
Threat force structure and offensive tactics incorporate the concepts of mass, maneuver, and speed. Daily offensive rates of advance of 60-100 kilometers are expected during nuclear operations, and 30-60 kilometers under conventional conditions. To achieve these significant rates, to maintain offensive momentum, and to avoid presenting lucrative targets for nuclear weapons, speed and bypass operations are emphasized in overcoming natural and manmade obstacles.
When it is necessary to attack a built-up area, the following basic concepts govern the deployment of forces at division level:
Classification of Built-Up Areas
SIZE ESTIMATED POPULATION CLASSIFICATION PERIMETER
100,000 Large more than or more 25 kms
50,000 to 15 kms to 100,000 Average 25 kms
less than less than 50,000 Small 15 kms
A surprise attack envisions a rapid, bold movement from the line of march by a strong advance detachment to secure an undefended or lightly defended built-up area. It seeks to avoid a costly, protracted street-by-street, house-to-house battle and permit attacking forces to continue beyond the area without reducing offensive momentum. The surprise attack seeks to preserve vital facilities such as bridges, railroads, airfields, key industrial complexes, and utilities.
The following figure illustrates how a motorized rifle division (MRD) might conduct a surprise attack with a reinforced M battalion (MRB) in the role of the advance detachment. The size of an advance detachment is determined by the size of the built-up area and expected resistance.
The advance detachment moves rapidly and attempts to avoid contact with defensive forces on the approaches to the objective. If little or no resistance is encountered, the advance detachment seizes the most important objectives (buildings) and key streets, splitting the area into isolated pockets of resistance, and destroys them piecemeal. Hasty defenses are organized to defeat counterattacks by the defending forces or to destroy defenders attempting to escape through the built-up area.
Airborne or helicopter-landed forces may support the advance detachment by sealing off flanks or the rear of the objective. These forces may also be employed as the advance detachment around or in the built-up area. An advance detachment operating outside the range of forward artillery receives intensified reconnaissance and close air support from high-performance aircraft and helicopter forces.
If the surprise attack fails, the advanced detachment is normally directed to seize a foothold in the outskirts or to seize an adjacent key terrain feature and wait for the main body to arrive.
Figure 3-3a Secure Key Objective
Figure
3-3b Seize A Foothold
A deliberate attack is conducted when the surprise attack has failed or when intelligence indicates a city is well defended. This attack involves larger forces, requires more detailed planning, and has a greater weight of artillery, mortar, and rocket fires than a surprise attack. The deliberate attack is characterized by:
Advanced reconnaissance activities include the study of large-scale maps, aerial photographs, and background intelligence reports. These data are updated by tactical intelligence from long-range reconnaissance patrols, agent reports, and electronic intelligence. Heliborne and airborne units may supplement ground reconnaissance and are normally targeted against specific key points in the urban area.
Reconnaissance functions are also frequently conducted by infiltrators disguised as refugees. Infiltrators or reconnaissance detachments may operate in the objective area for several days before an assault. Active reconnaissance may include the use of local residents to provide current essential information of the defender's activities. Raids by reconnaissance teams may be mounted for the purpose of capturing prisoners and documents. In some cases, raid/reconnaissance teams may be tasked to destroy selected critical facilities and defending forces prior to a deliberate attack.
Reconnaissance tasks include the determination of:
Figure 3-4 MRRs Isolating an Objective
* Command post, reserves, weapon positions, and supply locations.
Isolation
The preceding figure depicts first-echelon regiments of a motorized rifle division (MRD) isolating an objective area in order to deny reinforcement/resupply of defenders and block escape routes. Occasionally, an intentional exit may be permitted to entice defenders into open terrain where they can be attacked. After isolating the area, second-echelon forces may conduct a siege operation while first-echelon forces break contact and continue their advance. If the attacker's timetable permits, siege operations are preferred to avoid a costly direct assault and destruction of facilities needed to support future operations.
Bombardment
The deliberate attack is normally preceded by howitzer, mortar, rocket, and air bombardment. The intensity of the preparation is determined by the strength of defensive forces, the type building construction, and the density of fires required to suppress observation and fires.
First priority of fires is allocated to the main attack to destroy AT weapon positions and strongpoints on the area's edge. Artillery attached to assaulting units normally does not participate in the bombardment, but is reserved for direct fire employment against strongpoints on the outskirts and for support within the built-up area.
Other goals of the bombardment are to destroy or disrupt:
Smoke will normally be employed during artillery preparations to suppress the defenders while threat forces negotiate obstacles on the approaches and within the built-up area.
Assault
Habitually, simultaneous attacks are made on the flanks and rear to capture specific objectives and to splinter defenses. Frontal assaults are avoided and will be conducted only when an objective cannot be isolated or flanked.
During or immediately after preparatory fires, engineers move forward under the cover of smoke and high explosives to neutralize barriers and breach minefields on routes into the city. First-echelon assault groups attack to secure a foothold 2-3 blocks in depth. After securing the initial foothold and rupturing the outer defenses, the first echelon may continue to attack, or the second echelon is passed through the foothold and attacks along designated routes from one objective to another.
The attack within the built-up area is characterized by bold, rapid movements to secure assigned objectives. Buildings along the route are not routinely searched or secured unless resistance is strong. Bypassed defenders are left for elimination by following echelons or the reserve. If the leading echelon is stopped or slowed, the following echelons or reserve may be committed around engaged forces and continue to the objective.
Figure 3-6 MRB Attack in Built-up Area
Figure 3-7 2d Echelon Committed Around Engaged 1st Echelon
Detected weaknesses in the defense are exploited by aggressive mounted attacks. Infantry mounted on tanks, in BMPs, or trucks fire while moving rapidly along streets to assigned objectives. Tactical doctrine stresses the use of underground routes in the attack. Such routes that cannot be used are blocked or mined to prevent infiltration into the attacking force's rear.
In the assault of an objective, Threat forces isolate the position by fire or by securing adjacent buildings. Isolation is stressed to prevent defenders from escaping to a rearward position and to deny reinforcement. Attached artillery and tanks are habitually used to suppress defensive fires and to breach walls to provide entrances for assaulting infantry. Assaulting infantry avoid advancing along streets where they would be exposed to effective defensive fire. They seek surprise by attacking the objective from the flank or rear. Routes to the objective may consist of available underground passages such as subways, tunnels, and sewers, or passages blasted through intervening building walls. Once the assault of an objective begins, supporting fires shift to upper stories and to adjacent buildings. Assaulting infantry aggressively clear, in sequence, ground floor, basement, stairways, and each ascending floor. Once secured, the position is immediately prepared to repel counterattacks.
Round-the-clock operations are stressed to maintain uninterrupted momentum of the attack and to reduce casualties. Night operations against built-up areas are conducted to:
When surprise cannot be achieved, night assaults may be preceded by direct artillery/tank fires against strongly defended buildings. Direct support artillery and mortars seal off the objective area to prevent defenders from withdrawing or being reinforced. Illumination is fired to guide forces, illuminate objectives, and to dazzle the defender's night vision devices.
After securing assigned objectives and eliminating significant defensive opposition, assault groups normally establish defensive positions beyond the built-up area and prepare to continue the attack. Detailed clearance operations are normally passed to following units or to security formations.
The size and composition of the force allocated to seize a built-up area is determined by the area's size, shape, type of buildings, street patterns, and strength of defending forces. Attacking forces are not evenly distributed around the built-up area, but are employed over the most favorable avenues of approach. Generalized attack zones for motorized rifle units are:
Division 4 to 6 kilometers Regiment 2 to 3 kilometers Battalion 400 to 600 meters Company 200 to 300 meters
The figure below depicts the second-echelon motorized rifle regiments of a motorized rifle division conducting a deliberate attack. The 1st MRR, designated as the main attack force, is moving with three motorized rifle battalions (MRBs) in column. This formation is normally employed when defenses are organized in depth or when the city is configured in an elongated pattern.
The 2d MRR is organized with two MRBs in the first echelon, one MRB (-) in the second echelon, and a MR company as the reserve. Thi formation is normally employed when defenses are organized on the city's edge or when attacking a shallow built-up area.
Figure 3-9 Motorized Rifle Regiments Conducting the Deliberate Attack
Figure 3-10 Attack of Built-up Area by Reinforced Motorized Rifl Battalion (Main
Attack)
The basic unit in built-up area warfare is the reinforced MRB. The above figure illustrates a type first-echelon MRB (assault detachment) designated as the main attack force. The battalion is reinforced by attaching a tank company, a battery of SP artillery for direct fire, one company of engineers, and one NBC reconnaissance section. An additional artillery battalion is normally placed in direct support for indirect fire missions in the battalion's zone. Missions normally assigned to a MRB making the main attack in the first echelon include:
Missions normally assigned a second-echelon MRB include:
Reserve MRBs are prepared to:
Attachments to the MR company are further attached to platoons, providing each platoon with at least one tank or artillery weapon and a share of engineers. These attachments allow decentralized/independent operations by platoons in seizing specific objectives. Frequently, these attachments may be made down to squad level.
Figure 3-11 Motorized Rifle Platoon Assaulting Strongpoint.
Tanks
Tanks supporting MR companies may be employed as a platoon, in sections, or singly with an MR squad. Generally, a rifle squad provides close-in security for each tank, relying on the tank for protection and fire support. Tanks also support the attack by firing on suspected positions, smashing barricades, and engaging opposing armor.
Artillery
The difficulty of centralized fire control and the decreased effectiveness of indirect fires within built-up areas is recognized. For these reasons, over 50 percent of the available artillery may be attached and employed in a direct fire role to create breaches in buildings, walls, and barricades. Within the built-up area, SP artillery weapons are frequently attached to infantry platoons/squads. The artillery commander normally collocates with the MRB commander.
Mortars
Mortars cover avenues of enemy troop movements, such as street intersections and alleys. Mortar firing positions are placed behind walls or inside buildings close to their targets.
Engineers
Engineers are attached to MR platoons and squads with the following missions:
Massed fire from heavy batteries of the division and regimental artillery groups is used against large buildings, strong enemy fortified positions, and in a counterfire role. Other missions for these groups include interdiction and destruction of enemy supply installations, headquarters, and communication centers.
Threat doctrine stresses the following offensive fundamentals which should be considered when planning the defense of a built-up area.
Built-up areas not essential to overall success of offensive operations will be bypassed and isolated if possible. When an attack is required, Threat forces will attempt to secure key built-up areas by a surprise attack from the march before defenses have been established.
The deliberate attack is characterized by isolating the objective area, conducting an intense pre-assault air and artillery bombardment, and by multiple assaults on the flanks and rear of the area to be secured. Combined arms assault groups orient on securing objectives and will bypass and isolate centers of resistance. Detailed clearance of each building is normally assigned to follow-on units.
MR companies are reinforced with tanks, artillery, antitank guns, and engineers. MR companies are expected to operate independently. The majority of organic artillery is attached to assaulting units and employed in a direct fire role.
Underground systems are considered to be key avenues of approach. Tall structures that are likely observation posts are high-priority artillery targets.
The enemy will accept isolation of attacking units and heavy losses to secure assigned objectives and to maintain attack momentum.
This section describes US defensive doctrine for operations on urbanized terrain and provides detailed considerations to be applied by commanders during planning. Readers must be familiar with defensive planning as outlined in organizational How-to-Fight manuals and understand how the enemy attacks.
Commanders at each level must decide how best to integrate manmade features into their overall scheme. In some cases, commanders may be directed to defend a built-up area, a line of communications, or an industrial complex whose retention provides significant advantage within the framework of the defensive plan of a higher level commander. The decision to defend such an area may also be made because of specific tactical advantages accruing to the defender assigned responsibility for an area. In all cases, the elements of urban sprawl must be analyzed in conjunction with natural terrain in order to determine how to enhance weapons effectiveness to slow, block, canalize, and destroy the enemy.
Built-up areas, like forests, hills, or other terrain features, may be incorporated in the plan for the defense of an urban area in order to:
The fundamentals of the defense do not change on the urban battlefield. To apply them, commanders must understand the characteristics and components of urban sprawl, the advantages and disadvantages they offer, and how they impact on the capabilities of units and weapons during the conduct of the defense.
Understand the Enemy
The first part of this chapter supplements Threat data provided in other source documents by describing how the enemy may attack on urbanized terrain. When planning an urban defense, commanders at each level must place themselves in the enemy's position, view the battlefield from his perspective, and fit his concepts, formations, and weapons to the terrain. This estimate enables the defender to narrow the list of tactical options available to the attacker and identify his most probable courses of action. See the Battlefield.
Once the commander has organized the defense to counter the variety of attack options available to the enemy, he must aggressively seek to learn where the enemy is, how he is organized, which way he is going, and in what strength.
Although the characteristics of urbanized terrain may complicate the intelligence collection effort, the advantage lies initially with the defender. Commanders at all levels must know the terrain over which they will conduct the defense. Reconnaissance, surveillance, and target-acquisition resources must be applied as far forward as possible along likely avenues of approach to provide data to higher commanders.
Security forces operating from covered and concealed positions in depth complement electronic warfare support measures and tactical imagery activities by limiting the enemy's ground reconnaissance and infiltration capabilities.
On the urban battlefield, the attacker must forfeit, at least in part, the advantages of cover and concealment in order to move and mass; his routes of advance are limited and more clearly defined, enhancing the defender's target-surveillance capability; and he must use increased communications to coordinate the concentration of his forces, which reduces his ability to achieve surprise.
The defender must use his knowledge of the terrain and enemy to see the battlefield more accurately than the enemy, to prevent surprise, and to maximize reaction time for maneuver forces.
Concentrate at the Critical Times and Places
The ability of the defender to concentrate rapidly throughout the battle area may be limited by restrictive terrain. In order to maintain a favorable mobility differential over the attacker, the commander must use his knowledge of the terrain. Routes must be selected, reconnoitered, and prepared for the forward and lateral movement of forces to be concentrated. The obstacle value of the urban terrain complex must be reinforced to slow the attacker.
Detailed movement data and explicit traffic control plans are essential. Lines of communication which are dependent on bridges, overpasses, or tunnels should not be used unless suitable bypasses are available. Weather or land usage patterns, as well as other manmade features, may limit the mobility of armored and mechanized forces. Greater reliance must be placed on an initial positioning of forces which accepts risk zones along the least probable avenues of approach. These zones may be covered primarily by air or ground screening forces and fires. On urbanized terrain, it is more difficult to recover from an erroneous decision which concentrates maneuver elements too early or at the wrong place. In this maneuver-restrictive envirOnment, increased emphasis on the use of artillery and attack helicopters as the first increments of concentration is required. As the battle progresses, the commander's intimate knowledge of the terrain is used to maintain the mobility advantage.
Fight as a Combined Arms Team
A detailed analysis of the urban-terrain complex provides the basis for allocating and organizing available forces to accomplish the defensive mission. Cross-reinforcement of maneuver elements will normally be required in order to match unit capabilities to the terrain mix. In the more open portions of the urban environment, armored and mechanized forces may play the dominant role. As the density of manmade features increases, the employment of mechanized or dismounted infantry, supported by armor and engineers, becomes increasingly important. If it is necessary to fight within a built-up area, the role of infantry supported by other arms becomes dominant. Field and air defense artillery, air cavalry, and attack helicopters are employed throughout the battle area to maximize the combined arms team's effectiveness, multiply its combat power, and enhance its survivability.
Exploit the Advantages of the Defender
The already significant advantages of the defender become more pronounced on the urbanized battlefield. A common threat running through the discussion of the application of these fundamentals is the defender's familiarity with the terrain. Every action by the attacker is made more difficult because he must feel his way through this complex of manmade and natural terrain features. The defender can prepare the ground in advance, build and reinforce obstacles, and select firing positions and observation posts, many of which require improvement only. He can reconnoiter and improve routes between battle positions to shift forces and to supply them. Mutually supporting positions are often readily available. This pattern of favorable positions should enable the commander to strike the enemy repeatedly, slowing and disrupting him, inflicting losses, and making him vulnerable to multiple, violent, local counterattacks. In many areas, terrain restrictions may enable attacks by fire alone.
Defensive planning on the urbanized battlefield follows the process described in organizational How-to-Fight manuals. The basic roles of the covering force, main battle, and rear areas remain unchanged. The following specific considerations assume added importance.
Organization of the Battlefield.
On the urbanized battlefield, the defender fits his forces to the ground by utilizing the terrain to take maximum advantage of its natural and manmade features. Urban sprawl adds strength to the active defense by providing covered and concealed positions and restricting the attacker's mobility and observation.
Dismounted infantry can contribute to this defense by occupying battle positions or strongpoints around which the mobile battle is fought. In restrictive urban terrain, dismounted forces may be required in order to find the enemy, deny him the ability to close without being detected, and then fight the close-in battle.
If the retention of a built-up area is required, the defense may assume the characteristics of a position defense organized in depth and supported by strong mobile forces.
Covering Force Area (CFA). The urban area defense begins with mobile combined arms covering forces deployed well forward of the main battle area (MBA).. Company team and task force battle positions are organize in depth to control approaches to the main battle area, with emphasis placed on using natural and manmade features which offer cover and concealment or restrict opposing force maneuver. Small villages and strip areas may be incorporated in the defensive scheme in the same manner as other terrain features.
Increased engineer support is required to reinforce the obstacle nature of the terrain and maintain withdrawal and attack routes. Mixed caliber artillery contributes to deception in this environment where it is difficult for the enemy to see the battlefield and assists the CFA commander in maintaining the continuity of the defense from successive positions. The air defense artillery umbrella must extend over the CFA to deny the enemy the use of aerial observation and attack assets. Air cavalry and attack helicopters should be employed throughout the CFA, taking advantage of the terrain which limits detection by ground surveillance and screens aerial maneuver.
The transfer of the enemy by the covering force must not result in an easing of pressure or allow the enemy to gain momentum. Once detailed coordination has been accomplished, the restrictive nature of the urban terrain complex, its obstacles, and readily available defensive positions may facilitate the actual hand off.
Main Battle Area (MBA). The defending commander must be aware of the impact that urbanization of the terrain within the MBA will have on his ability to defend. Consideration should be given to the restrictive or compartmentalized areas caused by the urbanization process and to the advantages or disadvantages which the areas may offer the defender. It is possible that some of these areas may fall within risk areas which provide the enemy with covered and/or concealed infiltration routes into the MBA. In such cases, responsibility for risk areas must be clearly delineated between adjacent units. If the urban terrain includes villages, small towns, and strip areas, it might be advantageous to incorporate these features within company/team or task force battle positions. Such features can provide excellent cover and concealment to defending forces and are frequently mutually supportable.
As previously noted, it may become necessary to designate a built-up complex within the MBA as critical to the defense of the urban area. When this situation arises, it is imperative to initiate the defense of the urban area as far forward as possible to facilitate the defense of the built-up area and to avoid a protracted combat-in-cities battle.
The figure below portrays typical defensive sectors for company/team organizations assigned a defend mission in various types of built-up areas. With less restrictive missions, these typical widths may be extended. Final sector dimensions are defined based on a detailed analysis as described in appendix A.
Figure 3-17. Typical Company Team Defensive Sectors by Type Built-up Area
A 300-500 Meters
B 400-600 Meters
C 500-800 Meters
D 500-900 Meters
E 700-1100 Meters
Commanders should consider the potential value of urban features as obstacles to attacking forces. Frequently urban areas sit astride, or otherwise dominate, high-speed avenues of approach into and through the MBA. If urban areas cannot be bypassed easily, they may reduce the momentum of the enemy's attack and his ability to maneuver. In these instances, the defending commander must be prepared to capitalize on the situation. Conversely, the defending commander must also appreciate the limitations which urban areas can place on his own ability to maneuver, particularly during active defense operations.
A primary concern to commanders defending a built-up area is to avoid becoming isolated by enemy forces. In planning the defense, the commander can normally make two assumptions concerning this matter. The first assumption is that although the built-up area may not occupy terrain which is dominant, it normally has dominant terrain adjacent to it on at least one side. The second assumption is that, doctrinally, the enemy will attempt to bypass and isolate a built-up area by securing the adjacent dominant terrain before the built-up area itself is directly attacked. Therefore, the defending commander must integrate surrounding dominant terrain into his defensive scheme in order to preclude being bypassed and isolated.
Should the defense of an urban area develop to the point that operations within the built-up area itself are required, the defending commander must consider the nature of the built-up area and the characteristics which are unique to fighting there. The nature of the built-up area includes such aspects as the size of the area, the type of construction used for buildings, the density of the buildings, and the street pattern or layout of the built-up area. These aspects may vary considerably from one part of the built-up area to another, but each will impact in some way on the manner in which the defense of the area is conducted.
Built-up areas generally degrade command and control by reducing the capability of direct observation of subordinate units and by interfering with radio communication. Zones of responsibility are compressed into relatively small areas with shorter unit frontages.
Maneuver room is restricted, placing a greater reliance on infantry-heavy forces. Fields of fire and observation are also reduced, leading to violent, independent small-unit actions at close quarters. The battle within a built-up area can be expected to be multidimensional. It may be fought simultaneously above the ground, on roof tops, in buildings, at street level, and below the ground in sewers and subway systems.
Rear Area. The functions and organization of the division rear area are not significantly changed in an urban environment. Within larger urban areas, mobility may be restricted by damage to and along lines of communication from air or artillery attacks. Detailed traffic control may be required to maintain the forward and rearward flow of combat service support elements. Additionally, the everpresent threat of attack by small elements infiltrating through the MBA or from air assault forces increases. Internal security and self-defense responsibilities expand because of the limited availability of and reduced mobility of reserves.
When the MBA defense is organized around brigade battle areas, security during logistical movements and for combat support units located outside these battle areas becomes increasingly critical. If brigade support areas are located behind battle areas, additional coordination may be required to establish priority for security and movement between the various brigade, division, and corps support elements.
Limited Visibility Operations
The defender on the urban battlefield must be prepared to counter enemy attacks launched at night or under other conditions of limited visibility. Within built-up areas, the attacker may use such conditions to attempt to extend his reconnaissance, infiltrate friendly positions, cross open areas, or secure limited objectives. To help defend against such operations, the following basic measures may be employed:
Urban warfare places a heavy strain on the command and control apparatus. Command of subordinate units and the control of fires is complicated by restrictive terrain, the proximity of opposing forces, reduced communications capabilities, and the numerous small, isolated battles that may be fought simultaneously throughout the urban complex.
The primary control measures used are battle areas, battle positions, and sectors. Phase lines, checkpoints, and restrictive fire control measures may also be used to simplify reporting and control.
Timely and accurate situation reports are more critical to the commander in this environment. Distances between forces on the urban battlefield are reduced; an unreported breakthrough may splinter defensive cohesion and seriously jeopardize the entire defense. Commanders must constantly be informed of critical actions to enable rapid assessment and reaction. Commanders should be located well forward and within FM (secure) ranges of committed forces.
An in-depth, well-thought-out concept of defense provides the latitude for repositioning uncommitted units and quickly integrating them into the defense.
Achievement of an integrated, flexible, and responsible command and control system will require:
This section provides examples of how units from corps through battalion task force may defend on an urbanized battlefield. The urbanized terrain offers certain benefits and problems for the defender to consider in developing his defensive plan. A keen awareness of the urban environment and how it can affect the battle is stressed for all levels of command. In order to reduce the amount of repetitive general information, each special situation flows from the preceding material. Therefore, they should be read in sequence. General planning considerations and procedures described in detail in organizational How-to-Fight manuals are not repeated here.
Strategic intelligence sources indicate that enemy units are preparing to initiate offensive operations. All available information points to the fact that an attack crossing the international boundary on a wide front is imminent. The commander, 10th (US) Corps, along with other allied commanders has bee directed to implement standing defense plans immediately.
The mission of the lOth (US) Corps is to establish covering forces along the international boundary and defend in sector.
This Corps is a forward-deployed organization consisting of the following major combat units:
It is estimated that the enemy will attempt to penetrate the corps defenses on a narrow front once beyond the border region in order to pass second-echelon forces into the corps rear area. Although the enemy may be required to secure selected urban areas for use as logistical bases to support the offensive drive, it can be expected that first-echelon forces will attempt to bypass urban areas and leave the attack of those built-up areas to second-echelon forces.
During the development of the corps defense plan, specific consideration was given to land use patterns, major lines of communication, and physical terrain forms. Each of these elements impacts upon defensive operations, and, when properly utilized, may offer significant advantages by adding to the combat power of the defender.