Infantry Drills

FM 3-21.8 – Chapter 8 – Section III – Planning Considerations

Section III – Planning Considerations

8-34.     The Army warfighting functions incorporate a list of critical tactical activities that provide a structure for leaders to prepare and execute the defense. Synchronization and coordination among the warfighting functions are critical for success.

Movement And MANEUVER

8-35.     Effective weapons positioning enables the platoon to mass fires at critical points on the battlefield to effectively engage the enemy in the engagement area. (See Section IV for more information on engagement area development.) The platoon leader must maximize the strengths of the platoon’s weapons systems while minimizing its exposure to enemy observation and fires.

8-36.     Mobility focuses on the ability to reposition friendly forces, including unit displacement and the commitment of reserve forces. The company commander’s priorities may specify that some routes be improved to support such operations. Countermobility channels the enemy into the engagement area as it limits the maneuver of enemy forces and enhances the effectiveness of the defender’s direct and indirect fires.

Depth and Dispersion

8-37.     Dispersing positions laterally and in depth helps protect the force from enemy observation and fires. Platoon positions are established to allow sufficient maneuver space within each position for in-depth placement of crew-served weapons systems and Infantry squads. Infantry fighting positions are positioned to allow massing of direct fires at critical points on the battlefield, as well as to provide overlapping fire in front of other fighting positions. Although the factors of METT-TC ultimately determine the placement of weapons systems and unit positions, the following also apply:

– Infantry squads can conduct antiarmor fires in depth with CCMS, which have a maximum range of 2,000 meters.

– Infantry squads can retain or deny key terrain if employed in strongpoints or protected positions.

– Infantry squads can protect obstacles or flank positions that are tied into severely restrictive terrain.

Flank Positions

8-38.     Flank positions enable a defending friendly force to bring direct fires to bear on an attacking force. An effective flank position provides the friendly defender with a larger, more vulnerable enemy target while leaving the attacker unsure of the location of the defender. Major considerations for successful employment of a flank position are the friendly defender’s ability to secure the flank, and his ability to achieve surprise by remaining undetected. Effective direct fire control (see Chapter 2, Employing Fires) and fratricide avoidance measures (see Chapter 5, Command, Control, and Troop-Leading Procedures) are critical considerations when employing flank positions.


8-39.     During defensive preparations, mobility focuses initially on the ability to resupply, CASEVAC, reposition, and the rearward and forward passage of forces, supplies, and equipment. Once defensive preparations are complete, the mobility focus shifts to routes to alternate, supplementary, or subsequent positions. The company commander will establish the priority of mobility effort within the company.


8-40.     To be successful in the defense, the platoon leader must integrate obstacles into both the direct and indirect fire plans. (Refer to FM 90-7, Combined Arms Obstacle Integration, for additional information on obstacle planning, siting, and turnover.) A tactical obstacle is designed or employed to disrupt, fix, turn, or block the movement of the enemy. Platoons construct tactical obstacles when directed by the company commander.

Disrupting Effects

8-41.     Disrupting effects focus a combination of fires and obstacles to impede the enemy’s attack in several ways, including breaking up his formations, interrupting his tempo, and causing early commitment of breaching assets. These effects are often the product of situational obstacles such as scatterable mines, and are normally used forward within engagement areas or in support of forward positions within a defensive sector. Normally, only indirect fires and long-range direct fires are planned in support of disrupting obstacles (Figure 8-1).

Figure 8-1. Disrupt obstacle effect.

Fixing Effects

8-42.     Fixing effects use a combination of fires and obstacles to slow or temporarily stop an attacker within a specified area, normally an engagement area (Figure 8-2). The defending unit can then focus on defeating the enemy by using indirect fires to fix him in the engagement area while direct fires inflict maximum casualties and damage. If necessary, the defender can reposition his forces using the additional time gained as a result of fixing the enemy. To fully achieve the fixing effect, direct and or indirect fires must be integrated with the obstacles. The company commander must specify the size of the enemy unit to be fixed.

Figure 8-2. Fix obstacle effect.

Turning Effects

8-43.     Turning effects (Figure 8-3) use the combination of direct and indirect fires and obstacles to support the company commander’s scheme of maneuver in several ways, including the following:

– Diverting the enemy into an engagement area and exposing his flanks when he makes the turn.

– Diverting an enemy formation from one avenue of approach to another.

– Denying the enemy the ability to mass his forces on a flank of the friendly force.

Figure 8-3. Turn obstacle effect.

Blocking Effects

8-44.     Blocking effects use the combination of direct and indirect fires and obstacles to stop an attacker along a specific avenue of approach (Figure 8-4). Fires employed to achieve blocking effects are primarily oriented on preventing the enemy from maneuvering. Because they require the most extensive engineer effort of any type of obstacle, blocking effects are employed only at critical choke points on the battlefield. Blocking obstacles must be anchored on both sides by existing obstacles (severely restrictive terrain). Direct and or indirect fires must cover the obstacles to achieve the full blocking effect. The company commander must clearly specify the size of enemy force that he intends to block.


Figure 8-4. Block obstacle effect.

Displacement and Disengagement Planning

8-45.     Displacement and disengagement are key control measures that allow the platoon to retain its operational flexibility and tactical agility. The ultimate goals of displacement and disengagement are to enable the platoon to maintain standoff range of the CCMS and to avoid being fixed or decisively engaged by the enemy.


8-46.     While displacement and disengagement are valuable tactical tools, they can be extremely difficult to execute in the face of a rapidly advancing enemy force. In fact, displacement in contact poses great problems. The platoon leader must therefore plan for it thoroughly before the operation and rehearse moving to alternate and supplementary positions if time permits. Even then, he must carefully evaluate the situation whenever displacement in contact becomes necessary to ensure it is feasible, and that it will not result in unacceptable personnel or equipment losses. The platoon leader must consider several important factors in displacement planning:

– The enemy situation (for example, an enemy attack with battalion-sized element may prevent the platoon from disengaging).

– Higher headquarters’ disengagement criteria.

– Availability of friendly direct fire to facilitate disengagement by suppressing or disrupting the enemy.

– Availability of cover and concealment, indirect fires, and smoke to assist disengagement.

– Obstacle integration, including situational obstacles.

– Positioning of forces on terrain (such as reverse slopes or natural obstacles) that provides an advantage to the disengaging elements.

– Identification of displacement routes and times that disengagement and or displacement will take place.

– The size of the friendly force available to engage the enemy in support of the displacing unit.

Disengagement Criteria

8-47.     Disengagement criteria dictate to subordinate elements the circumstances under which they will displace to alternate, supplementary, or subsequent defensive positions. The criteria are tied to an enemy action (such as one motorized rifle platoon advancing past Phase Line Delta) and are linked to the friendly situation. For example, they may depend on whether a friendly overwatch element or artillery unit can engage the enemy. Disengagement criteria are developed during the planning process based on the unique conditions of a specific situation. They should not be part of the unit’s SOP.

Direct Fire Suppression

8-48.     The attacking enemy force must not be allowed to bring effective fires to bear on a disengaging force. Direct fires from the base-of-fire element, employed to suppress or disrupt the enemy, are the most effective way to facilitate disengagement. The platoon may also receive base-of-fire support from another element in the company, but in most cases the platoon will establish its own base of fire. Employing an internal base of fire requires the platoon leader to carefully sequence the displacement of his elements.

Cover and Concealment

8-49.     Ideally, the platoon and subordinate elements should use covered and concealed routes when moving to alternate, supplementary, or subsequent defensive positions. Regardless of the degree of protection the route itself affords, the platoon should rehearse the movement. By rehearsing, the platoon can increase the speed at which it moves and provide an added measure of security. The platoon leader must make a concerted effort whenever time is available to rehearse movement in limited visibility and degraded conditions.

Indirect Fires and Smoke

8-50.     Artillery or mortar fires can be employed to assist the platoon during disengagement. Suppressive fires, placed on an enemy force as it is closing inside the defender’s standoff range, will disrupt his formations, slow his progress, and if the enemy is a mechanized force, cause him to button up. The defending force engages the enemy with long-range direct fires, then disengages and moves to new positions. Smoke may be employed to obscure the enemy’s vision, slow his progress, or screen the defender’s movement out of the defensive positions or along his displacement route.

Obstacle Integration

8-51.     Obstacles should be integrated with direct and indirect fires to assist disengagement. By slowing and disrupting enemy movement, obstacles provide the defender the time necessary for displacement. Obstacles also allow friendly forces to employ direct and indirect fires against the enemy. The modular pack mine system (MOPMS) can be employed in support of the disengagement to either block a key displacement route once the displacing unit has passed through it, or to close a lane through a tactical obstacle. The location of obstacle emplacement depends in large measure on METT-TC factors. An obstacle should be positioned far enough away from the defender so enemy elements can be effectively engaged on the far side of the obstacle while the defender remains out of range of the enemy’s massed direct fires.


8-52.     For the indirect fire plan to be effective in the defense, the unit must plan and execute indirect fires in a manner that achieves the intended task and purpose of each target. Indirect fires serve a variety of purposes in the defense, including:

– Slowing and disrupting enemy movement.

– Preventing the enemy from executing breaching operations at turning or blocking obstacles.

– Destroying or delaying enemy forces at obstacles using massed indirect fires or precision munitions (such as Copperhead rounds).

– Defeating attacks along dismounted avenues of approach using FPF.

– Disrupting the enemy to allow friendly elements to disengage or conduct counterattacks.

– Obscuring enemy observation or screening friendly movement during disengagement and counterattacks.

– Based on the appropriate level of approval, delivering scatterable mines to close lanes and gaps in obstacles, disrupting or preventing enemy breaching operations, disrupting enemy movement at choke points, or separating or isolating enemy echelons.


8-53.     Platoons are responsible for coordinating and employing their own protective obstacles to protect their defensive positions. To be most effective, these obstacles should be tied into existing obstacles and FPFs. The platoon may use mines and wire from its basic load or pick up additional assets (including MOPMS, if available) from the engineer Class IV or V supply point. (See Appendix F for details on MOPMS and mines.) The platoon, through the company, also may be responsible for any other required coordination (such as that needed in a relief in place) for recovery of the obstacle or for its destruction (as in the case of MOPMS).  A detail discussion of Protection can be found in Chapter 4.

8-54.     In planning for protective obstacles, the platoon leader must evaluate the potential threat to the platoon position and employ the appropriate asset. For example, MOPMS is predominately an antitank system best used on mounted avenues of approach, but it does have some antipersonnel applications. Wire obstacles may be most effective when employed on dismounted avenues of approach. FM 90-7 provides detailed planning guidance for the emplacement of protective obstacles.

8-55.     Protective obstacles are usually located beyond hand grenade range (40 to 100 meters) from a Soldier’s fighting position. They may extend out 300 to 500 meters to tie into tactical obstacles and existing restrictive or severely restrictive terrain. The platoon leader should therefore plan protective obstacles in depth and attempt to maximize the effective range of his weapons.

8-56.     When planning protective obstacles, the platoon leader should consider the amount of time required to prepare them, the resources available after constructing necessary tactical obstacles, and the priorities of work for the Soldiers in the platoon.

Wire Obstacles

8-57.     There are three types of wire obstacles: protective wire; tactical wire; and supplementary wire (Figure 8-5).

Protective Wire

8-58.     Protective wire may be a complex obstacle providing all-round protection of a platoon perimeter, or it may be a simple wire obstacle on the likely dismounted avenue of approach toward a squad position (Figure 8-6). Command-detonated M18 Claymore mines may be integrated into the protective wire or used separately.

Tactical Wire

8-59.     Tactical wire is positioned to increase the effectiveness of the platoon’s direct fires. It is usually positioned along the friendly side of a machine gun FPL. Tactical minefields may also be integrated into these wire obstacles or be employed separately.

Supplementary Wire

8-60.     Supplementary wire obstacles are employed to break up the line of tactical wire to prevent the enemy from locating platoon weapons (particularly CCMS and machine guns) by following the tactical wire.


Figure 8-5. Three types of protective wire obstacles.

Figure 8-6. Protective wire groups.

Obstacle Lanes

8-61.     The platoon may be responsible for actions related to lanes through obstacles. These duties may include overwatching lanes in the obstacle, marking lanes in an obstacle, reporting the locations of the entry and exit points of each lane, manning contact points, providing guides for elements passing through the obstacle, and closing lanes when directed.


8-62.     Survivability focuses on protecting friendly forces from the effect of enemy weapons systems. Survivability positions are prepared in defensive positions or strongpoints to protect weapons systems and rifle squads. Positions can be dug in and reinforced with overhead cover to provide rifle squads and crew-served weapons with protection against shrapnel from air bursts. The company may dig in ammunition prestocks at platoon alternate, supplementary, or subsequent defensive positions. The platoon leader may have time only to dig in positions that have the least amount of natural cover and concealment. Soil composition should also be a consideration in the selection of defensive positions. Sites to be avoided include those where the soil is overly soft, hard, wet, or rocky.

Air and Missile Defense

8-63.     The focus of an air and missile defense plan is on likely air avenues of approach for enemy fixed-wing, helicopters, and unmanned aircraft systems that may not correspond with the enemy’s ground avenues of approach. A platoon leader is not likely to emplace air defense assets, but he must be aware that higher headquarters may employ air defense assets near his defensive position. For a detailed discussion of air defense, see Section II, Chapter 4.


8-64.     In addition to the sustainment function required for all operations, the platoon leader should consider prestocking (also known as pre-positioning or caches). The platoon leader’s mission analysis (or guidance from the company commander) may reveal that the platoon’s ammunition needs during an operation may exceed its basic load. This requires the platoon to establish ammunition caches. The caches, which may be positioned at an alternate or subsequent position, should be dug in. Security should be provided by active or passive means (guarded or observed) to indicate when and if the cache is tampered with.

8-65.     The platoon must have a plan to recover their assets when quickly transitioning to the offense or counterattack or when disengaging.


8-66.     The intelligence warfighting function consists of the related tasks and systems that facilitate understanding of the enemy, terrain, weather, and civil considerations.  It includes tasks associated with ISR.  It is a flexible, adjustable architecture of procedures, personnel, organizations, and equipment.  These provide relevant information and products relating to the threat, civil populace, and environment to commanders.  Intelligence warfighting function focuses on four primary tasks:

(1)     Support to situational understanding.

(2)     Support to strategic responsiveness.

(3)     Conduct ISR.

(4)     Provide intelligence support to targeting.

Command And control

8-67.     The command and control warfighting function consists of the related tasks and systems that support commanders in exercising authority and direction.  It includes those tasks associated with acquiring friendly information, managing all relevant information, and directing and leading subordinates.


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