DEFENSIVE TASKS

3-10. There are three basic defensive tasks: area defense, mobile, and retrograde. Each contains elements of the others, and usually contains both static and dynamic aspects. Infantry platoons serve as the primary maneuver element, or terrain-controlling units for the Infantry company. They can defend area of operation, positions; serve as a security force or reserve as part of the Infantry company’s coordinated defense. (Refer to FM 3-90-1 for more information.)

3-11. As part of a defense, the Infantry platoon can defend, delay, withdraw, counterattack, and perform security tasks. The Infantry platoon usually defends, as part of the Infantry rifle company’s defense in the main battle area. It conducts the defense to achieve one or more of the following ─

• Gain time.
• Retain essential terrain.
• Support other operations.
• Preoccupy the enemy in one area while friendly forces attack in another.
• Wear down enemy forces at a rapid rate while reinforcing friendly operations.

AREA DEFENSE

3-12. An area defense concentrates on denying enemy forces access to designated terrain for a specific time rather than destroying the enemy outright. The focus is on retaining terrain where the bulk of the defending force positions itself in mutually supporting positions and controls the terrain between positions. The defeat mechanism is fires into engagement area, which reserve units can supplement. The leader uses the reserve force to reinforce fires, add depth, block penetrations, restore positions, counterattack to destroy enemy forces, and seize the initiative.

Organization of Forces

3-13. The leader organizes the defending force to accomplish information collection, reconnaissance operations; security; main battle area; reserve; and sustainment missions. The leader has the option of defending forward or defending in-depth. When the leader defends forward within an area of operation, the force is organized so most of available combat power is committed early in the defensive effort. To accomplish this, the leader may deploy forces forward or plan counterattacks well forward in the main battle area or even beyond the main battle area. If the leader has the option of conducting a defense in-depth, security forces and forward main battle area elements are used to identify, define, and control the depth of the enemy’s main effort while holding off secondary thrusts. This allows the leader to conserve combat power, strengthen the reserve, and better resource the counterattack.

Security

3-14. The leader balances the need to create a strong security force to shape the battle with the resulting diversion of combat power from the main body’s decisive operation. The leader usually allocates security forces to provide early warning and protect those forces, systems, and locations necessary to conduct the decisive operation from unexpected enemy contact.

Main Battle Area

3-15. The leader builds the decisive operation around identified decisive points, such as key terrain or high-payoff targets. The leader positions the echelon main body within the main battle area where the leader wants to conduct the decisive operation. The leader organizes the main body to halt, defeat, and ultimately destroy attacking enemy forces. The majority of the main body deploys into prepared defensive positions within the main battle area.

Reserve

3-16. The reserve is not a committed force. The leader can assign it a wide variety of tasks on its commitment, and it must be prepared to perform other missions. In certain situations, it may become necessary to commit the reserve to restore the integrity of the defense by blocking an enemy penetration or reinforcing fires into an engagement area.

Sustainment

3-17. The sustainment mission in an area defense requires a careful balance between establishing forward supply stocks of petroleum, oil, and lubricants (POL); barrier materiel; and ammunition in adequate amounts to support defending units and having too many supplies located in forward locations that they cannot be rapidly moved in reacting to enemy advances. All suitable POL, barrier materiel, construction equipment, and laborers can be lawfully obtained from the civil infrastructure reducing the defending unit’s transportation requirements. Likewise, maintenance and medical support with their associated repair parts and medical supplies also must be forward deployed.

Forms of Defensive Maneuver

3-18. Two forms of defensive maneuver within an area defense are defense in-depth and forward defense. The Infantry platoon is expected to be able to do both. While the Infantry company commander usually selects the type of area defense to use, the higher commander often defines the general defensive scheme for the Infantry company. The specific mission may impose constraints such as time, security, and retention of certain areas that are significant factors in determining how the Infantry company will defend.

Defense In-Depth

3-19. Defense in-depth reduces the risk of the attacking enemy quickly penetrating the defense. The enemy is unable to exploit a penetration because of additional defensive positions employed in-depth. (See figure 3-1.) The in-depth defense provides more space and time to defeat the enemy attack.

3-20. The Infantry platoon uses a defense in-depth when ─

• The mission allows the Infantry platoon to fight throughout the depth of the areas of operations.
• The terrain does not favor a defense well forward, and better defensible terrain is available deeper in the areas of operations.
• Sufficient depth is available in the areas operations.
• Cover and concealment forward in the areas of operations is limited.
• Weapons of mass destruction may be used.

Forward Defense

3-21. The intent of a forward defense is to prevent enemy penetration of the defense. (See figure 3-2.) Due to lack of depth, a forward defense is least preferred. The Infantry platoon deploys the majority of its combat power into forward defensive positions near the forward edge of the battle area. While the Infantry company may lack depth, the platoon and squads must build depth into the defense at their levels. The leader fights to retain the forward position, and may conduct counterattacks against enemy penetrations, or to destroy enemy forces in forward engagement area. Often, counterattacks are planned forward of the forward edge of the battle area to defeat the enemy.

3-22. The Infantry platoon uses a forward defense when ─

• Terrain forward in the areas of operations favors the defense.
• Strong existing natural or man-made obstacles, such as river or a rail lines, are located forward in areas of operations.
• The assigned area of operations lacks depth due to location of the area or facility to be protected.
• Cover and concealment in rear portions of the areas of operations is limited.
• Directed by higher headquarters to retain or initially control forward terrain.

MOBILE DEFENSE

3-23. Mobile defense is a defensive task that concentrates on destruction or defeat of the enemy through a decisive attack by a striking force. Mobile defenses focus on defeating or destroying the enemy by allowing enemy forces to advance to a point where they are exposed to a decisive counterattack by the striking force. The leader uses the fixing force to hold attacking enemy in position, to help channel attacking enemy forces into ambush areas, to retain areas from which to launch the striking force. Mobile defenses require an area of operation of considerable depth. The leader must able to shape the battlefield, causing an enemy to overextend its lines of communication, expose its flanks, and dissipate its combat power. Likewise, the leader must be able to move friendly forces around and behind the enemy force targeted to cut off and destroyed. Divisions or larger formations normally execute mobile defenses. However, the platoon may participate as part of the fixing force or the striking force.

Note. Units smaller than a division usually do not conduct a mobile defense because of inability to fight multiple engagements throughout the width, depth, and height of their area of operation, while simultaneously resourcing the striking, fixing, and reserve forces. Typically, the striking force in a mobile defense consists of one-half to two-thirds of the defender’s combat power.

3-24. Infantry platoons’ missions in a mobile defense are similar to missions in area defense and offensive missions. They are either a part of the fixing force or part of the striking force, not both. As part of the fixing force, platoons defend within their assigned area of operation, although the area of operation might be larger than usual. As part of the striking force, Infantry platoons plan, rehearse, and execute offensive tasks.

3-25. Platoons use the term “striking force” rather than the term “reserve” because “reserve” indicates an uncommitted force. The striking force is a committed force that has the resources to conduct a decisive counterattack as part of the mobile defense. The striking force decisively engages the enemy as it becomes exposed in attempts to overcome the fixing force. The striking force normally attacks a moving enemy force, normally armor heavy.

RETROGRADE

3-26. Retrograde is a defensive task involving organized movement away from the enemy. The enemy may force a retrograde or the leader may execute it voluntarily. In either case, the higher commander of the force executing the operation must approve retrograding.

3-27. Retrogrades are conducted to improve a tactical situation or preventing a worse situation from developing. Platoons usually conduct retrogrades as part of a larger force but may conduct independent retrogrades (withdrawal) as required. Retrograde operations can accomplish the following ─

• Resist, exhaust, and defeat enemy forces.
• Draw the enemy into an unfavorable situation.
• Avoid contact in undesirable conditions.
• Gain time.
• Disengage a force from battle for use elsewhere for other missions.
• Reposition forces, shorten lines of communication, or conform to movements of other friendly units.
• Secure favorable terrain.

3-28. The three forms of retrograde are ─

• Delay.
• Withdrawal.
• Retirement.

Delay

3-29. Delays allow units to trade space for time, avoiding decisive engagement and safeguard its forces. Ability of a force to trade space for time requires depth within the area of operation assigned to the delaying force. The amount of depth required depends on several factors, including the ─

• Amount of time to be gained.
• Relative combat power of friendly and enemy forces.
• Relative mobility of forces.
• Nature of terrain.
• Ability to shape areas of operations with obstacles and fires.
• Degree of acceptable risk.

3-30. Delays succeed by forcing the enemy to concentrate forces to fight through a series of defensive positions. Delays must offer a continued threat of serious opposition, forcing the enemy to repeatedly deploy and maneuver. Delaying forces displace to subsequent positions before the enemy is able to concentrate sufficient resources to decisively engage and defeat delaying forces in current positions. The length of time a force can remain in position without facing danger of becoming decisively engaged is primarily a function of relative combat power, METT-TC and weather. Delays gain time to ─

• Allow friendly forces to establish a defense.
• Cover withdrawing forces.
• Protect friendly force’s flanks.
• Allow friendly forces to counterattack.

Parameters of the Delay

3-31. Parameters of the delay are specified in the order for a delay mission. First, leaders direct one of two alternatives: delay within the area of operation or delay forward of a specified line or terrain feature for a specified time. The second parameter in the order must specify acceptable risk. Acceptable risk ranges from accepting decisive engagement in an attempt to hold terrain for a given time maintaining integrity of the delaying force. The order must specify whether the delaying force may use the entire area of operation or must delay from specific battle positions. A delay using the entire area of operation is preferable, but a delay from specific positions may be required to coordinate two or more units.

Alternate or Successive Positions

3-32. Leaders normally assign subordinate units contiguous area of operation that are deeper than they are wide. Leaders use obstacles, fires, and movement throughout the depth of assigned area of operation. If the leader plans the delay to only last a short time or the area of operation’s depth is limited, delaying units may be forced to fight from a single set of positions. If the leader expects the delay to last for longer periods, or sufficient depth is available, delaying units may delay from either alternate or successive positions.

3-33. In both techniques, delaying forces normally reconnoiter subsequent positions before occupying them if possible, and post guides on one or two subsequent positions. Additionally, in executing both techniques, it is critical the delaying force maintains contact with the enemy between delay positions. Advantages and disadvantages of the two techniques are summarized in table 3-1.

3-34. The alternate position technique normally is preferred when adequate forces are available and areas of operation have sufficient depth. Delays from alternate positions, two or more units in a single area of operation occupy delaying positions in-depth. (See figure 3-3.) As the first unit engages the enemy, the second occupies the next position in-depth and prepares to assume responsibility for the operation. The first force disengages and passes around or through the second force. It then moves to the next position and prepares to re-engage the enemy while the second force takes up the fight.

Watch the following video to learn more about Delays from alternate positions.

3-35. Delays from subsequent positions are used when assigned area of operation are so wide available forces cannot occupy more than a single tier of positions. (See figure 3-4.) Delays from subsequent positions must ensure all delaying units are committed to each of the series of battle positions or across the area of operation on the same phase line. Most of the delaying force is located well forward. Mission dictates the delay from one battle position or phase line to the next. Delaying unit movement is staggered so not all forces are moving at the same time.

Watch the following video to learn more about Delays from subsequent positions.

Withdrawal

3-36. Withdrawal is a planned retrograde operation, which a force in contact disengages from an enemy force, and moves in a direction away from the enemy. Although the leader avoids withdrawing from action under enemy pressure, it is not always possible. Withdrawal is used to preserve the force or release it for a new mission.

3-37. Withdrawals are inherently dangerous. They involve moving units to the rear and away from what is usually a stronger enemy force. The heavier the previous fighting and closer the contact with the enemy, the more difficult the withdrawal. Units usually confine rearward movement to times and conditions when the advancing enemy force cannot observe the activity or easily detect the operation. OPSEC is extremely important, especially crucial during the initial stages of a delay when most of the functional and sustainment forces displace.

Planning a Withdrawal

3-38. The leader plans and coordinates a withdrawal in the same manner as a delay. METT-TC applies differently because of differences between a delay and withdrawal. A withdrawal always begins under the threat of enemy interference. Because the force is most vulnerable when the enemy attacks, the leader plans for a withdrawal under pressure. The leader then develops contingencies for a withdrawal without pressure. In both cases, the leaders main considerations are to ─

• Plan a deliberate break from the enemy.
• Displace the main body rapidly, free of enemy interference.
• Safeguard withdrawal routes.
• Retain sufficient maneuver, functional/multifunctional support and sustainment capabilities throughout the operation supporting forces in contact with the enemy.

Assisted or Unassisted

3-39. Withdrawals may be assisted or unassisted. They may or may not take place under enemy pressure. These two factors combined produce four variations. (See figure 3-5.) The figure below depicts the mission graphic for a withdrawal and withdrawal under enemy pressure. The withdrawal plan considers which variation the force currently faces.

3-40. Leaders prefer to conduct a withdrawal while not under enemy pressure and without assistance. Actions by the enemy, as well as additional coordination needed because of presence of an assisting unit, complicate the operation.

3-41. During an assisted withdrawal, the assisting force occupies positions to the rear of the withdrawing unit and prepares to accept control of the situation. Both forces closely coordinate the withdrawal. A withdrawing force can receive assistance from another force in the form of ─

• Additional security for the area through which the withdrawing force will pass.
• Information concerning withdrawal routes (reconnaissance and maintenance).
• Forces to secure choke points or key terrain along withdrawal routes.
• Elements to assist in movement control, such as traffic control points.
• Required maneuver, direct fire support and sustainment, which can involve conducting a counterattack to assist the withdrawing unit in disengaging from the enemy.

3-42. During an unassisted withdrawal, the withdrawing unit establishes routes and develops plans for the withdrawal. It establishes the security force as a rear guard while the main body withdraws. Sustainment and protection forces usually withdraw first, followed by combat forces. As the unit withdraws, the detachment left in contact (DLIC) disengages from the enemy and follows the main body to its final destination.

3-43. In an unassisted platoon withdrawal, the platoon leader may designate one squad to execute the DLIC mission for the platoon, or constitute the DLIC using elements from the remaining rifle squads with the platoon sergeant as the DLIC leader. Figure 3-6 shows an example of an unassisted withdrawal.

3-44. In a withdrawal under enemy pressure, all units withdraw simultaneously when available routes allow, using delaying tactics to fight their way to the rear. When simultaneous withdrawal of all forces is not practical, the leader decides the order of withdrawal. Several factors influence this decisio─

• Subsequent missions.
• Availability of transportation assets and routes.
• Disposition of friendly and enemy forces.
• Level and nature of enemy pressure.
• Degree of urgency associated with the withdrawal.

Retirement

3-45. Retirement is a task employing to move a force not in contact to the rear. Retirement is a form of retrograde, which a force not in contact with the enemy moves away from the enemy. A retiring unit organizes for combat but does not anticipate interference by enemy ground forces. Typically, another unit’s security force covers the movement of one formation as the unit conducts a retirement. However, mobile enemy forces, unconventional forces, air strikes, air assaults, or long-range fires may attempt to interdict the retiring unit. The leader plans for enemy actions and organizes the unit to fight in self-defense. The leader usually conducts retirement to reposition his forces for future operations or to accommodate the current concept of the operation. Units conduct retirements such as tactical road marches where security and speed are the most important considerations. (Refer to chapter 5 of this publication for more information.)