FM 5-71-100 Chptr 4 Defensive Operations

CHAPTER 4 DEFENSIVE OPERATIONS

The main purpose of the defense is to defeat an enemy attack. While military operations focus on maintaining the initiative through offensive action, the defense is an inherent part of any offensive operation. The defense is only a temporary state to facilitate offensive action. The division uses the defense to gain time for force buildup or to economize forces in one sector while massing forces for an attack in another. Likewise, a division may use defensive operations immediately following a successful attack to secure its objectives, develop the situation further, rebuild combat power, or deal the enemy a final, decisive blow. In any case, the defense is a critical means to successful division offensive operations. Therefore, it is imperative that engineers understand the art of the defense.

Division and corps engineer forces play a vital role in giving the division a decisive edge while conducting the defense. Engineers must understand the characterstics of defensive operations and how they apply to engineer operations. They must also appreciate how both engineer forces and missions integrate into the division's defensive framework. The engineer estimate process remains as the base planning tool for integrating into division defensive plans. While the process remains the same, each step is tailored to the needs of defensive planning. These fundamentals of engineer integration into division defensive operations are equally applicable to armored or light divisions.

The unique nature of engineer support to armored or light divisions differences in their respective tactics, engineer organizations and capability, and METT-T. Later sections in this chapter are dedicated to engineer support of armored, light, and mixed division defensive operations. These sections use the defensive framework to establish a force-tailored foundation for engineers support to the security force; the MBA; and the reserve, deep, and rear operations.

CHARACTERISTICS OF DEFENSIVE OPERATIONS

To effectively support a defense, engineers must understand the four distinct characteristics of the defense and their relationship to engineer operations. Characteristics of division defensive operations are--

Preparation.

Disruption.

Concentration.

Flexibility.

Preparation

Defensive operations have a distinct preparation phase which is vital to the division's success. The defender arrives on the battlefield first and is afforded the opportunity to choose his ground and set the conditions for the battle. Engineer functions and forces are a critical component in setting the conditions for combat and giving the division the edge against an attacker.

The success of engineers in the preparation phase depends largely on the ability of the division engineer to conduct integrated planning with the division staff and parallel planning with subordinate unit staff engineers. The division engineer uses engineer channels to disseminate the information and intent needed to foster early planning at all levels.

At the division level, engineer planning and preparation must provide centralized focus for the defense, while allowing decentralized integration and execution. The division engineer uses the scheme of engineer operations, obstacle capability and control, and survivability guidance to focus the division's subordinate unit's engineer efforts. The division engineer resources subordinates through task organization and the allocation of Class IV/V (obstacle) supplies. This allows subordinates to anticipate limitations on their capabilities and prioritize and rapidly identify shortfalls in resources.

Engineer participation in division preparations is not limited to the close operation in the MBA. The division engineer considers the full range of engineer requirements of the total defensive framework: deep, security, MBA, reserve, and rear operations. Each element of the defensive framework is considered during engineer mission analysis and accounted for in the division scheme of engineer operations.

Disruption

The division defense includes a focused attempt to disrupt the enemy effort through deep, security, and deception operations. The division engineer works closely with the division staff to ensure that engineer functions are integrated into deep operations. For example, the division engineer may nominate deep targets that directly attack the enemy's engineer capability. Likewise, the division engineer ensures that engineer aspects of deep and MBA operations are mutually supportive. Engineers provide the security force with the countermobility needed to disrupt the enemy's attack early and the mobility it needs to fight a fluid battle. Deception can play a major role in disrupting the enemy's attack by targeting the enemy's decision cycle. Deception operations can employ a combination of forces and obstacles that cause the enemy to commit combat power prematurely or against a strength perceived as a weakness.

Concentration

In the defense, the division concentrates forces to exploit or create an enemy weakness. Engineers support the concentration of combat power by employing obstacles, constructing fortifications, and providing mobility to counterattack or reserve forces. The principal role of engineers is normally in the employment of tactical obstacles. Engineers employ tactical obstacles to support the scheme of maneuver and directly attack the enemy's maneuver. Tactical obstacles are integrated with the defender's fires to disrupt, turn, fix, or block enemy maneuver, concentrating combat power to create and exploit a weakness. Engineers also construct fortifications and protective obstacles to give the force an edge over enemy fires and to break an enemy assault. Defending from survivable positions is vital to maintaining concentration until the attacker is destroyed. Finally, engineers provide mobility to counterattack forces and reserves to allow the division to take offensive action and exploit a broken enemy attack.

Flexibility

Flexibility is a critical characteristic of division defensive operations. The division must retain the flexibility to employ counterattack and reserve forces and operate within the enemy's decision cycle. Engineers assist the division in maintaining flexibility through situational obstacles in the MBA, task organizing for rapid transition to the offense, and improving or maintaining the routes needed to shift forces. Engineers plan the use of situational obstacles in the MBA as be prepared missions that allow the commander to react to the enemy's attack. Situational obstacles can be employed by themselves or to reinforce the existing effort. The division engineer must recognize the mobility requirements inherent in maintaining the flexibility of division reserve and counterattack forces. He plans for mobility by task organizing engineers with these forces, controlling the division obstacle effort (obstacle control measures), and anticipating rapid transitions to the offense.

DEFENSIVE PATTERNS

Division defensive operations generally take one of two traditional patterns: mobile and area defenses. The fundamental difference between these patterns is their focus-and-defeat mechanism. The scheme of engineer operations to support division defensive operations is tailored to the type of defense. The focus of engineer effort, unit missions, and task organization are all inseparably linked to the focus-and-defeat mechanism of each type of defense. Therefore, the division engineer must understand the area and mobile defense and their implications on engineer functions and unit operations.

Mobile Defense

The focus of mobile defense is the destruction of the enemy attacker. The mobile defense is organized to permit the enemy to advance into a position which exposes him to counterattack and envelopment by a mobile reserve. Therefore, the mobile defense trades space and time for achieving a decisive advantage against the enemy. The defeat mechanism is a large, mobile reserve which must have combat power and mobility equal to or greater than the targeted force.

The division engineer must understand the implications of a force-oriented defense on both engineer functions and operations (Figure 4-1). Engineer support to the mobile defense concentrates on using obstacles to attack enemy maneuver and preserving the mobility of the friendly force. Obstacle planning is more closely linked to the enemy's most probable maneuver course of action than to terrain. It must support attacking the enemy's maneuver in a way that supports his destruction by counterattack. Consequently, obstacle planning is more restrictive than permissive and reduces the flexibility of the brigades. This serves to mass brigade obstacle effort at critical areas and preserves the mobility of the counterattack force in the MBA.

Survivability effort is also tailored to a force-oriented defense that trades space and time for creating an enemy weakness to exploit by counterattack. To create the conditions for counterattack, the brigades must fight the depth of their sectors from multiple primary and subsequent battle positions. Fortification efforts support fighting quick engagements from multiple positions by providing primary and alternate hull-defilade fighting positions in both primary and subsequent battle positions. The nature of the fight reduces the overall need for protective obstacles throughout the defense. Protective obstacle effort is concentrated in final subsequent positions where the penetration must be blunted to allow counterattack.

The defeat mechanism of the mobile defense is the counterattack by a large, mobile reserve with combat power and mobility superior to the targeted enemy force. The division engineer supports the mobility of the mobile reserve in two ways. First, he uses obstacle control measures to ensure that brigade obstacle efforts do not limit the mobile reserve's freedom to maneuver. Second, he ensures the mobile reserve has the necessary dedicated engineer support to maintain its mobility during the counterattack. It must be able to counter the enemy's offensive use of obstacles or reduce friendly obstacles as required by changes in the situation. Above all, the counterattack cannot be stalled by a lack of mobility. The division engineer must weigh the trade-offs between dedicating engineer forces to the counterattack and the obstacle and survivability requirements of the MBA.

Area Defense

The focus of the area defense is on the retention of terrain. The area defense is organized to absorb the enemy into an interlocked series of positions from which he can be destroyed. In this pattern, the defeat mechanism is the interlocking nature of defensive positions and small mobile reserves within subordinate defenses to defeat local penetrations. The area defense does not promise outright destruction of the attacker and may require other simultaneous or subsequent operations to achieve a decisive defeat of the enemy.

The division engineer must understand the implication of the area defense on M/S requirements and engineer operations (Figure 4-2). Likewise, the scheme of engineer operations orients on the retention of terrain and on enabling the division to concentrate fires from fixed positions. The location of key and decisive terrain plays a major role in organizing the area defense and becomes the focus of obstacle and survivability effort.

Division obstacle planning uses obstacle control measures to give maximum flexibility to the brigades while still focusing tactical obstacle effort around the retention of terrain.

Survivability effort must enable brigades to concentrate fire power from fixed positions. The division engineer must be sensitive to the increased fortification needs of the brigades in a division area defense. To fight from more fixed positions, the brigades may require primary, alternate, and supplementary turret-defilade positions. This is particularly true of brigades defending decisive terrain. The increased requirement for survivability also entails heavier employment of protective obstacles to break the attacker's assault.

Interlocking defensive positions and small, decentralized, mobile reserves are two key components of the defeat mechanism which the division engineer must consider during planning and preparation. He must ensure that the tactical obstacle effort of adjacent brigades is coordinated and mutually supporting and achieves an interlocking defense. Additionally, he ensures that the engineer task organization provides the brigades with dedicated mobility support of their respective mobile reserves.

ENGINEER PLANNING FOR DEFENSIVE OPERATIONS

The engineer estimate provides the planning framework for the division engineer in supporting a division defensive operation. However, the engineer estimate steps focus on different considerations that are peculiar to a defensive mission. See Figure 4-3 for typical examples. This tailored application of the engineer estimate ensures the proper integration of engineer functions into the division's tactical planning process.

The role of the division engineer involves identifying missions, allocating resources, and synchronizing and controlling engineer functions. By the nature of the defense, countermobility and survivability are the primary missions that drive engineer force, resource allocation, and synchronization. Therefore, planning for countermobility and survivability consumes the majority of the division engineer's time. The engineer estimate process incorporates the obstacle planning process. The obstacle planning process does not preempt the use of the engineer estimate. The engineer estimate provides the total integration of engineer functions (mobility, countermobility, survivability, topographic, and sustainment engineering) into the division planning process.

The challenge of a defending force is to strip away the enemy's initiative and create exploitable vulnerabilities. The answer to this challenge is obstacle integration. The synchronization of indirect and direct fires and tactical obstacle effects is crucial to being successful. Obstacle control, intent, and resourcing are top-down driven, while obstacle integration with fires is generally bottom-up. The obstacle planning process provides the foundation for this integration. The obstacle planning process steps are listed below:

1. Situation analysis.

2. Organization of the operation.

3. Mobility and future operations requirements.

4. Obstacle resourcing.

5. Scheme-of-obstacle overlay.

Figure 4-4 shows the interrelationship of the obstacle planning process and the engineer estimate. Before the obstacle planning process can be discussed, the echelons of obstacle planning and obstacle control principles must be understood.

Echelons of Obstacle Planning

Specific obstacle synchronization techniques and control measures are relative to maneuver planning levels--division, brigade, and task force or battalion. Divisions, brigades, and task forces plan obstacle zones, belts, and groups, respectively. In some cases, corps may designate obstacle zones to division. Normally, obstacle zone planning is initiated by division. These obstacle control measures permit tactical obstacle placement and focus subordinate units in their tactical obstacle effort. The obstacle control measures not only focus obstacle effort for subordinate maneuver commanders on specific areas of the battlefield but can provide guidance on the specific obstacle effects (disrupt, turn, fix, and block) on the attacking enemy. This additional guidance is provided by obstacle intent. Refer to Figures 4-5 and 4-6, for a summary of the echelons of planning and a sample graphic portrayal. Before discussing the functions of obstacle zones, belts, groups, and individual obstacles, obstacle intent must be defined.

Obstacle Intent. Designating the obstacle effect--disrupt, turn, fix, or block--is not enough to synchronize fires and obstacle effort or to complement the scheme of maneuver. In order to focus the entire force, the maneuver commander and his supporting engineer designate an obstacle intent. Obstacle intent describes how, in terms of obstacle effects, the commander will use tactical obstacles to effect the enemy's maneuver to the advantage of his fire plan (direct and indirect). The obstacle intent establishes a direct link with the obstacle and fire plans. To accomplish this integration and synchronization, obstacle intent contains three components: an obstacle effect, a target, and a relative location on the battlefield.

The obstacle effect is conveyed through the use of precise graphics. Figure 4-7, depicts the obstacle-effects graphics. The maneuver commander and staff engineer must understand the flexibility of these graphics. Each symbol represents exactly how the enemy's maneuver should be altered. For example, a turn symbol points to the desired direction for the enemy formation to follow. Refer to Figure 4-8, for examples of how obstacle belts alter the enemy's formation through the use of obstacle groups.

A target refers to the enemy whose ability to maneuver is the target of the obstacle and fire plans. The target is relative to the subordinate unit's force allocation ratio. An armored maneuver brigade conducting a prepared defense will normally fight an enemy division. Maneuver battalions and companies in a prepared defense will fight an enemy's brigades or regiments and battalions, respectively.

The relative location of the battlefield refers to the use of obstacle control measures. Figure 4-6, depicts the relative locations for each planning echelon. Obstacle zones and belts use an enclosed, unspecified obstacle symbol. Obstacle groups use the obstacle-effect symbol alone on the exact terrain where direct and indirect fires will be integrated and synchronized with individual obstacles.

The obstacle intent's components enable the force to focus, integrate, and synchronize combat power with obstacles. A fully developed obstacle intent brings together--

The situation template, by defining the target.

The scheme of maneuver, by giving relative location, force allocation with a defined target, and fire planning with maneuver subunit responsibilities.

The engineer plan, by giving obstacle effects on a defined target and relative location to focus obstacle effort.

Resource allocation, by giving obstacle effects and relative location, enabling the engineer to use obstacle resource planning factors.

Obstacle Control Measures. In order to effectively plan and focus the division's obstacle effort, the division engineer must understand the total realm of functions and principles for obstacle zones, belts, groups, and individual obstacles. His plan influences the obstacle planning process down to the obstacle-emplacing unit.

Obstacle zones. An obstacle zone is a graphic obstacle control measure used by divisions to designate an area in which subordinate brigades are authorized to emplace tactical obstacles. The division commander uses obstacle zones to control and focus the obstacle effort for subordinate units. The division's scheme of maneuver drives the shape and location of the obstacle zone. Obstacle zones are given to subordinate maneuver brigades and separate maneuver forces (for example, the division CAV squadron) and do not cross their boundaries. Responsibility for obstacles on a boundary is covered under flank coordination. By not crossing the subordinate boundaries, obstacle zones enhance C2, assign specific responsibilities, and facilitate future operations. Obstacle intents are not normally assigned to obstacle zones. The intent will be given only when the division commander deems it a division-essential task having a specific effect on an attacking enemy division. Obstacle zones drive the initial flow of obstacle material to the committed forces. Obstacle zone development will be discussed in detail later in this chapter.

Obstacle belts. An obstacle belt is a graphic obstacle control measure used by brigades to designate an area within an approved obstacle zone in which subordinate units are authorized to emplace tactical obstacles. Obstacle belts must be inside obstacle zones or approved by division. Brigade commanders use obstacle belts to focus countermobility effort and fire planning. The obstacle-belt intent specifies to task force commanders what effect the scheme of maneuver and obstacle must have on the enemy's ability to maneuver.

The maneuver brigade commander designates obstacle belts to his subordinate maneuver battalions based on the division's obstacle zones and the brigade's scheme of maneuver. Obstacle belts focus and synchronize the brigade's obstacle effort. They generally straddle the enemy avenue of approach that the maneuver battalions are allocated against. Tactical obstacles are only permitted within the confines of the obstacle-belt graphic.

This is the first echelon of obstacle planning where an obstacle intent must be given for each obstacle belt. A sample obstacle-belt intent would be, "The intent of obstacle belt A2 is to turn a motorized rifle regiment (MRR) on Avenue of Approach 2 and place the MRR in engagement area (EA) SKULL." The belt graphic and intent facilitate throughput of Class IV/V (obstacle) supplies to the maneuver battalions. The brigade engineer resources obstacle belts based on the belt intent, the standard planning factors, and the sum of the mobility corridors that the belt straddles. This provides an approximation of the linear obstacle effort needed to achieve the belt intent. Obstacle belts do not cross maneuver battalion boundaries for the same reasons that obstacle zones do not cross brigade boundaries.

Obstacle groups. An obstacle group is an array of individual tactical obstacles within an obstacle belt whose combined effect accomplishes a single obstacle intent (turn, block, disrupt, or fix). Obstacle groups must be inside an obstacle belt or approved by brigade. Battalion task force commanders designate obstacle groups to integrate individual obstacle effort and indirect and direct fires. Obstacle groups directly target the threat formation that the maneuver company and teams are allocated against. Groups combine individual obstacles to accomplish a single effect. Obstacle group effects have specific integration techniques with the direct- and indirect-fire organization of the EA.

The task force commander allocates groups (based on the obstacle-belt intent) and graphics along with the task force scheme of maneuver. The summation of the obstacle groups that the battalion directs must accomplish the obstacle-belt intent. In other words, if the battalion is given the responsibility for a turning obstacle belt, the task force commander is not limited to turning groups only. For example, the battalion commander could target a first-echelon enemy battalion with a disrupting obstacle group, followed by a blocking obstacle group that denies a specific mobility corridor, and ending with a turning obstacle group against other enemy battalions. The total effects of the obstacle groups are turning an attacking enemy regiment. See Figure 4-8, for examples.

Individual obstacles. There are four general categories of individual tactical obstacles. The individual obstacles are those in obstacle groups, directed obstacles, reserve obstacles, and situational obstacles.

Individual obstacles in obstacle groups. Individual obstacles are tailored to the obstacle group effect and the threat. For example, minefield densities, composition, pattern, depth, and frontage have specific norms for achieving the disrupt, turn, fix, and block obstacle effect. These norms facilitate platoon drills and obstacle resourcing. Refer to FM 20-32 for more information. When employed, tank ditches are used to complement turning and blocking obstacle groups. Leaders ensure individual obstacle siting is consistent with the obstacle group's in tent and overmatching weapons systems.

If the mobility corridor is restricted, then point obstacles can also achieve a specific effect. One point obstacle in a platoon or smaller mobility corridor could achieve a disrupt effect, while several point obstacles in depth along the same mobility corridor can achieve a fix effect. This is extremely useful in restrictive terrain and for armored ambushes. Predominantly, light forces use this technique in restrictive terrain against an armored threat. However, to achieve a block or turn, individual obstacle norms must be used.

Directed and reserve obstacles. A directed obstacle is an obstacle directed by a higher commander as a specified task to a subordinate unit. A reserve obstacle is an obstacle for which the commander restricts the execution authority. The commander usually specifies the unit responsible for obstacle emplacement, handover, and execution. The commander must clearly identify the conditions under which the obstacle is to be executed. Only the division commander can authorize directed or reserve obstacles outside of an obstacle zone. In turn, only the brigade commander can authorize directed or reserve obstacles outside of an obstacle belt. Brigade directed and reserve obstacles must be within an obstacle zone. The maneuver battalion commander can authorize obstacles anywhere in his directed obstacle belt. This control procedure ensures control of the entire tactical obstacle effort.

Situational obstacles. A situational obstacle is a tactical, obstacle-emplacement capability held in reserve. Execution is triggered by friendly actions, enemy actions, or a combination of the two. Reserve obstacles and situational obstacles are different. A situational obstacle can be shifted to different locations, whereas a reserve obstacle is located at a specific key location. A situational obstacle must be within the executing maneuver unit's obstacle control measure.

Situational obstacles contain the three components of obstacle intent (obstacle effect, a target, and relative location) and require integration into the decision support template to be executed effectively. The plan must identify the trigger action and execution criteria at a specific decision point and the necessary subunit instructions to emplace and cover the obstacle. The division engineer has three possibilities for employing situational obstacles. The first is to plan and execute the obstacle at division level. The second is to identify the obstacle intent and allocate the resources to a subordinate unit to execute. The third is to allocate the resources for a subordinate unit to plan and execute.

Guidelines for Planning Obstacle Control Measures. Planning guidelines can be established between obstacle control measures and the size of the enemy avenue of approach (Figure 4-9). In general, the commander assigns an obstacle control measure on the same size enemy avenue of approach he uses as a basis for arraying subordinate forces. For example, an armored or light division assigns obstacle zones to its brigades which are arrayed on division avenues of approach. However, a light division defending against a mechanized division arrays its brigades to defeat enemy mechanized regiments and brigades. The light division would designate obstacle zones on the mechanized regiment or brigade avenues of approach. As shown in Figure 4-9, the same logic applies to every echelon and obstacle control measures. The commander may use different guidelines based on the estimate of the situation, enemy, time, terrain, and troops available.

Obstacle Control Principles

Planning obstacle zones is an art. However, certain norms and principles and the planning process provide the structure to tailor obstacle zones to support the division commander's intent and scheme of maneuver. Understanding division and brigade doctrine provides the foundation for defensive norms and principles. Examples that the division engineer uses to provide this foundation are shown as follows:

FM 100-5, Chapters 8 & 9.

FM 5-100, Chapter 7.

FM 71-100, Chapter 5.

FM 71-3, Chapter 4.

FM 7-30, Chapter 4.

Echelons of obstacle planning and obstacle intent.

Engineer estimate.

Understanding brigade operations is critical for the division engineer in order to anticipate the needs of the maneuver brigade commander.

In general, obstacle zone planning is guided by three obstacle control principles for supporting division defense operations. These principles help shape the engineer countermobility effort for the division:

1. Supports the division's scheme of maneuver and the commander's intent.

2. Balances maximum flexibility versus focusing obstacle effort.

3. Facilitates future operations.

Supports the Division's Scheme of Maneuver and the Commander's Intent. The division engineer must understand the division's defeat mechanism, the division commander's vision of the operation, the division's main effort and when it changes, and the division's synchronization requirements across the battlefield framework (close, deep, and rear). These are the elements which ensure that obstacle zones support the division's scheme of maneuver and the commander's intent.

The defeat mechanism guides the division engineer in determining general areas that require obstacle effort and areas that must be free of obstacles or have restrictions (such as the division counterattack force's axis and objective). The defeat mechanism also drives the type and amount of engineer support to the subordinate units. The division commander's vision of the operation describes how the division will achieve the desired end state relative to friendly forces, the terrain, and enemy forces. This vision, along with the defeat mechanism, provides a general framework that brings together the elements of obstacle intent, target, effect, and relative location. The division engineer uses this framework to generally envision how subordinate maneuver commanders will fight. This is critical in anticipating the needs and pushing resources to the maneuver brigades.

The division's main effort and when it changes gives the division engineer a guide in determining obstacle zone priorities and weighting the main effort with engineer resources (manpower and materials). Certain synchronization requirements impact obstacle-zone planning across the defensive framework. The division engineer considers division control and synchronization measures as he develops the obstacle zone design (see the next principle).

Balances Maximum Flexibility Versus Focusing Obstacle Effort. Designing obstacle zones is a balancing act between providing maximum flexibility and focusing tactical obstacle employment for the subordinate maneuver commander. Maneuver brigades are normally given sectors to defeat the attacking enemy but may be given a battle position or strongpoint. The battle position and strongpoint are more restrictive control measures. Defending in sectors gives the brigade commanders the freedom to maneuver and also decentralizes fire planning; whereas, the battle position dictates where the majority of the brigade's combat power will be positioned. Even with a more restrictive control measure as the battle position, brigades still require flexibility in tactical obstacle employment. The strongpoint is the most restrictive, and obstacle zone flexibility is greatly reduced and focused.

The division engineer provides the required flexibility with obstacle zone graphics through two dimensions: width and depth. The obstacle zone permits the brigade commander to employ tactical obstacles to complement his decentralized fire planning and his allocation of maneuver battalions, whether in sector or battle position. The maneuver brigade is assigned a sector or battle position based on the attacking enemy's combat power along a specific avenue of approach. At bare minimum, the width of the obstacle zone encompasses the avenues of approach. The maximum flexibility for an obstacle zone width is the entire subordinate's sector. The commander must understand that a zone covering an entire sector may restrict his ability to seize the initiative with a counterattack. Ideally, this risk should be considered during war gaming. Two exceptions for not providing this flexibility are facilitating future operations (discussed in the next principle) and obvious no-go terrain (against an enemy armored force), which prevents the enemy's ability to maneuver.

The depth of the obstacle zone is tailored to the division's scheme of maneuver and the commander's intent. Specific phase lines normally aid in tailoring the depth of the obstacle zone. For example, one brigade might be given the mission to defend well forward in the sector. The obstacle zone would facilitate this intent by allowing less depth. Typical graphics that aid in focusing the depth of an obstacle zone are on-order boundary changes, battle handover lines (BHLs), rear boundaries, forward edges of the battle area (FEBAs), lines of departure (LDs), lines of contact (LCs), fire-control lines (fire-support coordination lines (FSCLs), no-fire areas (NFAs), coordinated fire lines (CFLs)), passage lanes and corridors, and phase lines controlling friendly force positioning.

Facilitates Future Operations. To facilitate future operations, the division engineer uses obstacle zones as a restriction of tactical obstacle employment. Directed and reserve obstacles are the only exceptions for obstacles outside an obstacle control measure. The division's need for future mobility drives the need to restrict tactical obstacles. The division's counterattack force's axis and objective are standard examples for the division's future mobility needs. Another example is for the division to reposition forward as a subcomponent of the corps plan. The restrictions fall into two categories: decreasing flexibility and obstacle restrictions. Decreasing flexibility involves reducing the depth and width of individual obstacle zones. Shaping obstacle zones so that they do not overlap the counterattack axis and objective ensures the freedom of the counterattack force. Obstacle restrictions place limits on the method, type, and location of obstacles authorized to be emplaced within an obstacle zone or belt. Typical examples are allowing surface-laid mines only, restricting the use of antihandling devices, and specifying a no-later-than self-destruct time for scatterable mines. These obstacle restrictions facilitate future occupation and clearing of the obstacles by friendly forces.

Obstacle Planning Process

The echelons of obstacle planning and obstacle control principles provide the foundation for the obstacle planning process. At division level, the staff and engineer plan zones to control and focus obstacle effort for subordinate units. There are two techniques for developing obstacle zones and resourcing the zones with obstacle capability. One technique is to develop tentative belts, group the belts into zones, and resource the zones with obstacle capability based on the tentative belts. That is the technique used for these scenarios.

Another technique develops zones and task organization based on the scheme of maneuver and resources the zones with obstacle capability based on the division main effort, priorities, and task organization. This technique is normally used when time is a critical factor in the planning process. This technique involves some risk. Zones are developed based on division-level graphics.

Like the engineer estimate, obstacle planning steps are conducted concurrently as the scheme of maneuver is developed.

Situation Analysis. The goal of situation analysis is twofold for the division engineer. They must know the templates (doctrinal, situation, and event) that the division staff develops and the EBA. The key questions the division engineer concentrates on are--

How will the enemy allocate his combat power?

Where will the enemy array (two levels down) his forces and his formation norms?

When will the enemy attack?

How will the enemy weight his main effort?

What are the enemy's objectives and tactical options or alternatives?

How will the enemy use his engineer and mobility assets? (Focusing on mobility for his forward forces and countermobility for his flanks.)

The answers to these questions provide the division engineer the foundation for understanding and participating in the development of scheme of maneuver and engineer operations. This specifically shows how, where, and when the enemy will attack and where he is going (his objectives). The event template could also identify vulnerabilities or windows of opportunity which effect tactical obstacle employment.

Organization of the Operation. The division staff and G3 develop courses of action using the steps outlined below:

1. Analyze relative force ratios.

2. Array initial forces.

3. Develop scheme of maneuver.

4. Determine C2 means and maneuver control measures.

5. Prepare course of action statements and sketches.

The division engineer must know how the G3 develops the course of action. With the information gained from the situation analysis, the G3's array of friendly forces is based on the situation template and relative force ratios. For example, a ratio of 1:3 and 1:16 are the norms for a prepared defense and delay. The G3 takes his array of forces and develops a scheme of maneuver and determines C2 measures and requirements. The engineer sketches tentative obstacle belts to support the array of forces and the scheme of maneuver. This provides the initial start in tailoring obstacle zones to support the scheme of maneuver for that particular course of action.

The array of friendly forces, scheme of maneuver, and C2 measures and requirements aid the division engineer in envisioning the subordinate maneuver commanders' fight. Basically, the division engineer considers the two obstacle-zone dimensions. The obstacle zones for the division must complement the defeat mechanism. General guidelines can be used in relation to the defensive patterns, as mentioned earlier. The division engineer uses the array and allocation of friendly forces on specific avenues of approach and maneuver control measures to sketch proposed obstacle zone boundaries.

Mobility and Future Operations Requirements. The division engineer alters the proposed obstacle zones based on the division's mobility requirements and future operations. The second and third obstacle control principles (supports the division's scheme of maneuver and the commander's intent and facilitates future operations) are directly applicable for this step. The division engineer identifies areas which must be free of tactical obstacles and where obstacle restrictions are required to facilitate future operations. These areas cause the proposed obstacle zone's boundaries to be adjusted and specific restrictions (if applicable) assigned to certain zones. Other mobility operations, such as a passage of lines on lanes, may require division reserve obstacles. The obstacle zones are finalized and tied to maneuver graphics and terrain.

Obstacle Resourcing. There are two basic ways to resource obstacle zones. One technique is to allocate resources based on task organization. For example, if the division has 15 engineer companies, the resource allocation for each company is 1/15 of the resources available after the main effort has received their initial resource allocation.

Another technique is to resource the obstacle zones based on the division commander's intent; scheme of maneuver; and subordinate maneuver units' subunit instructions, which have been captured with tentative obstacle belts. The division engineer patterns obstacle intents based on assumptions of how the subordinate maneuver commander will fight. Complete understanding of the situation analysis step facilitates this process. The width of the avenue of approach that the assumed obstacle belt straddles is multiplied by the obstacle intent resource factor (indicated below).

Obstacle effect	Resource planning factor
Disrupt	0.5
Turn	1.2
Fix	1.0
Block	2.4

This provides the amount of linear obstacle effort required in the obstacle belt. The division engineer can sum the total linear effort required for all the planning belts and translate this sum into manpower, material, and time required using standard planning factors and obstacle packages.

The division engineer must also anticipate the subordinate maneuver brigades' survivability requirements. The EBA analysis of friendly capabilities of organic and corps engineer forces provides an approximation of the survivability capabilities within the division engineer battalions supporting the maneuver brigades (HHC for division light engineer battalions). The subordinate brigades' missions drive the allocation. As a norm, a brigade conducting an area defense requires a more intense blade effort than a mobile defense. Based on standard survivability planning factors, the division engineer can task organize corps engineer assets based on the anticipated needs of the committed brigades.

At the end of this step, the division engineer overlays the necessary engineer C2 requirements over their allocation of resources. This is inputted into the division's task organization. The obstacle-zone graphics, obstacle restrictions, responsibilities, and special considerations are finalized.

Scheme-of-Obstacle Overlay. The scheme-of-obstacle overlay is normally an appendix to the engineer annex at division level. The scheme-of-obstacle overlay contains the following elements:

Engineer task organization.

Obstacle-zone graphic.

Obstacle-zone table depicting responsibility and priority.

Obstacle intent (three components), if applicable.

Passage lanes that require reserve obstacles, if applicable.

Obstacle restrictions by obstacle zone, if applicable.

This overlay provides the subordinate maneuver commanders and their engineer staff the necessary tools to initiate the planning process.

ENGINEER SUPPORT TO AN ARMORED DEFENSE

In the defense, armored divisions seek to maximize their firepower, mobility, and shock effect. They may defend by initially delaying the enemy to determine his intentions and then by launching strong counterattacks against his flanks and rear in prepared areas. FM 71-100 further describes how armored divisions conduct defensive operations. Engineer planning focuses on each area of the defensive framework--deep, security, MBA, reserve, and rear operations. The division engineer uses the engineer estimate to identify engineer missions; synchronize mobility, countermobility, and survivability; and allocate resources. The obstacle planning process previously discussed is the tool for integrating obstacles into the division scheme of maneuver.

The following is a division scenario illustrating the integration of engineer operations into the division defensive framework.

Division Scenario

The division's mission is to conduct a defensive operation to defeat an attacking corps consisting of three mechanized divisions forward of phase line (PL) LAKE. The graphic portrayal of the division's scheme of maneuver and engineer organizations available are depicted in Figure 4-10. Corps will conduct deep operations forward of PL SEA, targeting the enemy's advance guard. The division's scheme of maneuver is a four-phase operation:

Phase 1 - Preparation/counterreconnaissance.

Phase 2 - Defense forward of PL STREAM.

Phase 3 - Counterattack.

The following is a list of the key subunit instructions:

1st Brigade
1. Defeat first-echelon division forward of PL STREAM.
2. Delay back to PL LAKE, creating a perceived salient for Phase 3.

2nd Brigade
Defend forward of PL STREAM, allowing no penetration larger than platoon (+) size.

3rd Brigade
Counterattack (Phase 3) into objective (OBJ) VIPER to defeat the second-echelon division.

Aviation Brigade
Counterattack (Phase 3) into OBJ COBRA, targeting C2 and CSS elements of the second-echelon division and corps.

Calvary Squadron
1. Screen between PL RIVER and PL OCEAN.
2. Conduct battle handover with 1st and 2nd brigades.

Deep Operations

The division engineer, as noted in Chapter 1, focuses on supplementing the IPB, HVT nominations, and the use of situational obstacles. The corps' covering-force operation could limit the division's deep operation for targeting HVTs and situational obstacles. However, during the division's counterattack (Phase 3), the employment of situational obstacles (area denial artillery munitions (ADAMs)/remote antiarmor mine system (RAAMS) (limited range) or Gator) helps to isolate regiments in the second-echelon division. Coordination between the division and corps is required. If authorized, the division engineer establishes an obstacle zone to support this employment of situational obstacles. Since the brigades have limited capability in "seeing deep", this coordination must be planned and executed at division level. The division engineer, along with the G2, G3, and other staff officers, as required, identify the obstacle intent, locations, and timing in relation to the execution criteria and decision points.

Security Operations

The CAV squadron is the division's covering force. Their mission is to screen between PL RIVER and PL OCEAN. The division engineer must understand the impact of the screen mission versus a guard or cover security mission. A screen provides early warning; whereas, a covering force that is given a guard or cover mission protects the MBA force and conducts screens, attacks, defends, and delays, as required. The obstacle effort required increases from the screen or guard missions to the cover mission. See Figure 4-11 for a sketch of the CAV squadron.

The screen is a very decentralized fight. The division engineer anticipates that the CAV could employ three disrupting obstacle belts. These tentative belts were grouped into obstacle zone ALPHA. This means the obstacle zone must facilitate maximum flexibility to employ tactical obstacles. PLs RIVER (BHL) and SEA (division forward boundary) impact on the obstacle zone's design. The obstacle zone's forward limit can be directly tied to PL SEA. PL RIVER is the BHL. The BHL needs to be controlled by the MBA forces in order to have a successful acceptance of the fight. The division engineer adjusts the rear boundary of the obstacle zone forward of PL RIVER, allowing MBA forces to employ tactical obstacles to support the battle handover. See Figure 4-12 for an illustration of obstacle zone ALPHA. The division engineer considers scatterable mines to aid the CAV's disengagement. The CAV can be reinforced with modular pack mine systems (MOPMs), air or ground Volcano, and ADAMs' and RAAMS's allocations (requires coordination with the FSCOORD).

Mobility and hasty survivability are critical to the CAV. The EBA analysis reveals the CAV's need for assault bridging. Marking lanes through obstacles and identifying fords and combat trails for egress routes are other mobility tasks in support of the CAV. The CAV requires numerous hull-defilade positions in depth versus fully developed and concentrated turret-defilade positions. As Figure 4-12 indicates, an engineer company is attached to the CAV squadron.

MBA and Reserve Operations

The division defeats the enemy corps in the MBA. Therefore, the priority for the division engineer's planning is supporting MBA operations. The division engineer includes support to the division's reserve when considering MBA requirements. In this division scenario, the brigade missions and engineer considerations are different. Refer to Figure 4-13 for MBA operations analysis.

1st Brigade. 1st brigade has two fights--forward of PL STREAM and forward of PL LAKE. The division engineer considers the mobility and countermobility requirements for the brigade's mission forward of PL STREAM and its mission to delay back to PL LAKE. Based on these considerations and in order to keep the division's counterattack axis free of obstacles, the division engineer plans two obstacle zones for 1st brigade (Figure 4-14).

The obstacle zone for the brigade's mission forward of PL STREAM must encompass the BHL (PL RIVER). The brigade sector has two regimental avenues of approach. The division engineer anticipates that 1st brigade could employ one blocking and two fixing obstacle belts. These tentative belts were grouped into obstacle zone BRAVO. To give the brigade commander maximum flexibility, the width of this obstacle zone must cover the two regimental avenues of approach. To facilitate the division's counterattack, the division engineer restricts the depth of the obstacle zone. These requirements dictate the shape of obstacle zone BRAVO. The division engineer anticipates that 1st brigade will require resources for two fixing belts in obstacle zone BRAVO.

The division engineer must recognize the brigade's need for tactical obstacles for their defense forward of PL LAKE. The division engineer anticipates that 1st brigade could employ two blocking obstacle belts. These tentative belts are grouped into obstacle zone CHARLIE to support this 1st brigade mission. The division engineer allocates resources for two blocking belts.

The division engineer plans for passage of the CAV. He recommends to the G3 that lane BLUE be restricted from any obstacle emplacement. Any request to emplace an obstacle on the route during the preparation and counterreconnaissance phases must be forwarded to division for consideration as a division reserve obstacle.

2nd Brigade. The division engineer uses the same approach taken with 1st brigade. The shape of obstacle zone DELTA follows the same logic of zone BRAVO. However, in order to support the commander's intent and show a strong defense forward, the rear boundary is pushed forward of PL STREAM. This should cause a concentration of countermobility effort along the FEBA to PL RIVER. Lane RED would have the same obstacle restriction as lane BLUE.

3rd Brigade. The initial focus is the mobility of the division's counterattack force. See Figure 4-15 for counterattack analysis. The obstacle zones shapes facilitate the future operation. The situational analysis and EBA aid in identifying 3rd brigade's mobility needs. Specifically, the division engineer's analysis of the enemy's scatterable mine and flank obstacle-employment capability will determine if 3rd brigade needs to breach enemy minefield. At the end of the attack, 3rd brigade conducts a hasty defense orienting in obstacle zone BRAVO. Close coordination between 1st and 3rd brigades is required. Specific coordination instructions will be identified for both brigade staffs and supporting engineer battalions.

Aviation Brigade. The aviation brigade is conducting a supporting attack into the second-echelon division's rear (OBJ COBRA). Tactical obstacles would aid the attack helicopters in their fight. The division engineer tailors obstacle zone ECHO to support only the fight in OBJ COBRA. The allocation of scatterable mines and the priority of employment will shift to the aviation brigade during the counterattack phase. The division engineer contemplates which scatterable assets to allocate to the aviation brigade. Ground-emplaced assets are ruled out immediately due to the lack of ground security. Air Volcano is an option. The division staff must consider the status of SEAD missions and the ability of the enemy to engage the Blackhawk delivering the mines. This rules out the air Volcano as the choice asset. Gator could be used if allocated, and SEAD/Joint SEAD (JSEAD) missions target local threats. ADAMs and RAAMS are available. ADAMs and RAAMS's allocations are coordinated with the FSCOORD to support the aviation brigade. Due to this allocation, an engineer staff planner must be sent to the aviation brigade to assist in ADAMs and RAAMS employment planning.

Rear Operations

Rear operations outlined in Chapter 1 are applicable. The DIVEN headquarters relies heavily on corps support. They concentrate on the division's needs to sustain the force. The DIVEN headquarters assigns missions to the CSE company to maintain the LOCs and to construct facilities for the main support battalion and corps support command (COSCOM) units in the division rear area. See Figure 4-16 for a sketch of the rear area. The routes for the division's counterattack force through the division rear area must be created or maintained (Figure 4-17).

The DIVEN headquarters must plan to maintain the mobility along the LOCs from the DSA to the brigade support areas (BSAs). They must anticipate contingencies to react to the enemy's use of scatterable mines. The corps engineer battalion is assigned this contingency. Unexploded ordinance (UXO) is an explosive ordnance disposal (EOD) mission. Requests for EOD support go to the division REAR CP for action. If EOD support is not available or the saturation of UXOs is too great for the EOD unit, engineers could assist in this mission. The DIVEN REAR CP keeps tabs on EOD missions if the UXO area effects the division's mission.

The survivability of sustainment operations in the rear area is essential to maintaining combat operations. Engineer survivability is supported through fortifications and protective obstacles. The DIVEN headquarters, along with the REAR CP, plan for survivability of all units in the rear area. The support is tailored to the base cluster defense plan. See Figure 4-18 for an example. The DIVEN headquarters recommends to the REAR CP the priorities of support. The priorities are based on four factors:

1. Vulnerability of the base cluster.

2. Ability of the units in the base cluster to defend themselves.

3. Criticality of the unit to the success of the division mission.

4. Recuperability of the unit and its assets in the base cluster.

Establishing priorities is only the first step. The threat must be understood and the base cluster defense designed to counter the threat. The following protective obstacle recommendations are based on the likelihood of the threat (threat levels) and whether the threat is ground-mounted, air-inserted, or terrorist:

Ground threat - Protective obstacles are antitank (AT) heavy.

Air-inserted threat - Protective obstacles are antipersonnel (AP) heavy, using AP mines and wire.

Terrorist - Force-protection techniques are employed.

The division staff must assess the enemy's ability to deliver fires onto the division rear and its effect on sustainment operations. The DIVEN headquarters, along with the REAR CP, determines and prioritizes fortification efforts and requirements based on this assessment. The DIVEN headquarters resources Class IV supplies, blade equipment, and engineers based on these priorities and amount of effort.

The fortification and protective obstacle effort for engineers in the rear area fall into two categories: advisory and missions. The engineers in the rear area advise base cluster defenses on fortification techniques and quality control measures. The fortification missions for engineer forces focus on protecting key C2 nodes, equipment, and vital materials. The cluster priorities guide the DIVEN headquarters in allocating assets to the units in the rear area.

The DIVEN headquarters plays a major role in coordinating, tracking, and troubleshooting the division's push of Class IV/V (obstacle) supplies forward to the brigades. See Chapter 6 for a detailed CSS discussion. Their goal is to get corps assets to throughput the material to the task force sector and coordinate haul support dedicated to hauling obstacle material. The assault float bridge (AFB) company could also be used as a hauling asset, if their principal employment is not required. The DIVEN headquarters plans for other rear area missions as listed below:

Rear area damage control.

Host-nation support.

Support to the tactical combat force.

The engineer support and planning for rear operations require dedicated engineer representation at the REAR CP. Even though the MBA consumes the majority of the DIVEN headquarters's planning effort and engineer forces, support to the rear operations is essential to the success of the division's close operation.

Scenario Conclusion

The defensive framework is a tool that provides a structured analysis of the engineer requirements across the battlefield. Figure 4-19 shows the general overlay that would be an appendix to the engineer annex. The DIVEN headquarters will use the scheme of engineer operations, the subunit instructions, and the engineer annex of the division OPORD to put the plan into action. The obstacle zones and reserve obstacles are part of the maneuver brigades' subunit missions. The engineer brigade's OPORD will cover the division engineer battalion's task organization to 1st, 2nd, and 3rd brigades and detailed instructions on the internal engineer brigade operations and engineer units under engineer brigade control.

ENGINEER SUPPORT TO A LIGHT DEFENSE

The light division is primarily organized, equipped, and trained to defeat light enemy forces. The light division is capable of defending against a mechanized enemy force in the right terrain and with the right mission when appropriately augmented with additional forces and support. Light forces capitalize on their ability to operate in restrictive terrain where mounted forces lose the tactical mobility advantage. The light division normally defends by assigning a sector to each brigade, allowing maximum freedom of maneuver for decentralized operations.

Light brigades fight by positioning forces in depth from reverse slope positions along restrictive mobility corridors on carefully selected and prepared terrain. Light forces engage the enemy at choke points and obstacles with direct and indirect fires and then maneuver through the restricted terrain to alternate positions. In short, they use the entire sector to progressively slow and weaken the enemy. Positioning techniques and the careful use of terrain will deny the enemy the advantage of being able to bring total combat power to bear on the light force.

The DIVEN headquarters must understand the tactics employed by the light division in order to effectively integrate M/S operations into the division defense. Engineer planning focuses on each area of the defensive framework--deep, security, MBA, reserve, and rear operations. The DIVEN headquarters uses the engineer estimate to integrate all engineer functions (mobility, countermobility, survivability, topographic, and sustainment engineering) into the division planning process. The obstacle planning process is the tool for integrating obstacles into the division scheme of maneuver.

The following is a division scenario which illustrates the integration of engineer operations into the division defensive framework.

Division Scenario

The light division is attached to a joint task force (JTF) for this operation. The JTF is defending with a division in the north, the light division in the center, and a host-nation division in the south. The JTF commander has positioned the light division in an economy-of-force role in restrictive terrain. The division's mission is to conduct a defense in sector, deny the enemy use of a key mobility corridor, slow the enemy's momentum, and create opportunities for subsequent JTF attacks. The enemy is a mixed force consisting of both mechanized and light forces, with a mission to attack and destroy the JTF lodgment. Figure 4-20 shows the division's scheme of maneuver and the engineer organizations available.

The division will conduct the operation in three phases:

Phase 1 - Preparation/Counterreconnaissance.

Phase 2 - Covering force area (CFA) battle.

Phase 3 - MBA battle.

The following is a list of the key subunit instructions:

1st Brigade
1. Defend in the sector initially forward of PL BLUE.
2. Conduct the battle hand-off with the CAV squadron at PL GREEN.
3. Block dismounted avenue into 2nd brigade's sector.
4. Allow no penetration of PL RED by platoon-sized or larger elements.

2nd Brigade
Defend in the sector forward of PL BLUE, destroying first-echelon regiments.

3rd Brigade
1. Defend in the sector forward of PL RED, destroying remaining enemy elements.
2. Allow no penetration of PL RED by platoon-sized or larger elements.

Aviation Brigade
1. (Phase 1) Provide security for the division.
2. (Phase 2) Conduct security force operations between PL GREEN and PL BLACK.
3. (Phase 2) Conduct battle hand-over with 1st and 2nd brigades.
4. (Phase 3) Act as division reserve. On-order attack to destroy second-echelon regiments of the first-echelon division in EAs BEAR and LION.