5-1. The Infantry platoon and squad use the defense to occupy—a tactical mission task in which a unit moves into an area to control it without enemy opposition (FM 3-90)—and prepare positions and mass the effects of fires on likely enemy avenues of approach or mobility corridors. Avenue of approach is a path used by an attacking force leading to its objective or to key terrain. Avenues of approach exist in all domains (ADP 3-90). Mobility corridors are areas that are relatively free of obstacles where a force will be canalized due to terrain restrictions allowing military forces to capitalize on the principles of mass and speed. While the offense is the most decisive type of combat operation, the defense is the stronger type. The inherent strength of the defense is the defender’s ability to occupy positions before an attack and use the available time to improve those defenses.
Characteristics Of The Defense
5-2. Successful defenses share the following characteristics: disruption, flexibility, maneuver, mass and concentration, operations in-depth, preparation, and security. Defenses are aggressive. Defenders use all available means to disrupt attacking enemy forces and isolate them from mutual support to defeat them in detail. Defenders seek to increase their freedom of maneuver while denying it to attackers. Defenders use every opportunity to transition to the offense, even if only temporarily. As attackers’ losses increase, they falter, and the initiative shifts to the defenders. Defenders strike swiftly when the attackers reach their decisive point(s). Surprise and speed enable counterattacking forces to seize the initiative and overwhelm the attackers’ concentration, flexibility, maneuver, and operations in-depth. (See FM 3-96 for additional information.)
Disruption
5-3. Defenders disrupt attackers’ tempo and synchronization with actions designed to prevent them from massing combat power. Disruptive actions attempt to unhinge the enemy’s preparations and, ultimately, enemy’s attack. Methods include defeating or misdirecting enemy reconnaissance forces, breaking up their formations, isolating their units, and attacking (for example, conduct aggressive combat patrols [see chapter 7]) or disrupting their systems.
Flexibility
5-4. The defense requires flexible plans. Planning focuses on preparation in-depth, use of reserves, and ability to shift the main effort. Defenders add flexibility by designating supplementary positions and designing counterattack plans. Planned flexibility only works when leaders recognize—and act on—the emerging conditions that necessitate that planned flexibility. Defenders can have a flexible plan but if they do not act because they are wedded to the base plan, they still lose the opportunity to regain the offensive element of conventional warfare.
Maneuver
5-5. Maneuver allows the defender to take full advantage of AO and to mass and concentrate when desirable. Maneuver, through movement in combination with fire, allows the defender to achieve a position of advantage over the enemy to accomplish the mission. It also encompasses defensive actions such as security force operations in the security area and security patrol activities in the main battle area and rear area.
Mass And Concentration
5-6. Defenders seek to mass the effects of overwhelming combat power where they choose and shift it to support the main effort. To obtain an advantage at decisive points, defenders economize and accept risk in some areas; retain and, when necessary, reconstitute a reserve; and maneuver to gain local superiority at the point of decision. Defenders accept risk in some areas to mass effects elsewhere. Obstacles, security forces, and fires can assist in reducing risk.
Operation In-Depth
5-7. Operations in depth—the simultaneous application of combat power throughout an area of operations (ADP 3-90)—improves the chances for success while minimizing friendly casualties. Quick, violent, and simultaneous action throughout the depth of the defender’s AO can hurt, confuse, and even paralyze an enemy force just as it is most exposed and vulnerable. Such actions weaken the enemy’s will and do not allow all early enemy successes to build the confidence of the enemy’s Soldiers and leaders. In-depth planning prevents the enemy from gaining momentum in the attack. Synchronization of main and supporting efforts facilitate mission success.
Preparation
5-8. The defense has inherent strengths. The defender arrives in the AO before the attacker and uses the available time to prepare. These preparations multiply the defense’s effectiveness. Preparations end only when the defenders retrograde or begin to fight. Until then, preparations are continuous. Preparations in-depth continues, even as the close fight begins.
Security
5-9. Security helps deceive the enemy as to friendly locations, strengths, and weaknesses. It also inhibits or defeat enemy reconnaissance. Security measures (for example, security patrols and counterreconnaissance [see paragraphs 7-183 to 7-184]) provide early warning and disrupt enemy attacks early and continuously.
Note. Counterreconnaissance is a tactical mission task that encompasses all measures taken by a unit to counter enemy reconnaissance and surveillance efforts (FM 3-90). Counterreconnaissance is not a distinct mission, but a component of all security operations and local security measures. It prevents hostile observation of a force or area. It involves both active and passive elements and includes combat action to destroy or repel enemy reconnaissance units and surveillance (both air and ground) assets.
Defensive Operations
5-10. A defensive operation is an operation to defeat an enemy attack, gain time, economize forces, and develop conditions favorable for offensive or stability operations (ADP 3-0). The three types of defensive operations are area defense (see section III), mobile defense (see note on page 5-59), and retrograde (see section IV). Each contains elements of the others and usually contains both static and dynamic aspects.
5-11. These three operations have significantly different concepts and pose significantly different problems. Each defensive operation is dealt with differently when planning and executing the defense. As with offensive operations, defensive operations can result in non-physical effects, such as those generated in the information environment—the aggregate of social, cultural, linguistic, psychological, technical, and physical factors that affect how humans and automated systems derive meaning from, act upon, and are impacted by information, including the individuals, organizations, and systems that collect, process, disseminate, or use information (JP 3-04).
5-12. For example, the use of deception in support of operations security can be highly effective at gaining time and tactical deception can support the economization of forces. Infantry forces use the three types of defensive operations to deny enemy forces advantages, each has its own focus—
- Area defense focuses on terrain.
- Mobile defense focuses on the movement of enemy forces.
- Retrograde focuses on the movement of friendly forces.
5-13. Infantry rifle platoons serve as the primary maneuver element or terrain-controlling units for the Infantry rifle company. They can defend within an AO or battle position or serve as a security force or a reserve as part of the Infantry rifle company’s or Infantry battalion’s coordinated defense. (See ATP 3-21.10 and ATP 3-21.20 for additional information.)
5-14. As part of a defense, the platoon can (although not all-inclusive) defend, delay, withdraw, counterattack, block, fix, turn, or perform security operations. 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.
Common Defensive Control Measures
5-15. The defending leader controls defensive operations by using control measures to provide the flexibility needed to respond to changes in the situation and allow the defender to concentrate combat power at the decisive point(s). Defensive control measures within the organization of forces of an AO includes designating the security area, the main battle area, within the close area, with its associated forward edge of the battle area, and rear area with its echeloned support areas. The defender can use battle positions and additional direct fire control and fire support coordination measures in addition to those control measures to synchronize the employment of combat power. The defender designates a disengagement line(s)—a phase line located on identifiable terrain that, when crossed by the enemy, signals to defending elements that it is time to displace to their next position (ADP 3-90)—to trigger the displacement of subordinate forces. (See FM 3-96 for additional information.)
Security Area
5-16. A security area is that area occupied by a unit’s security elements and includes the areas of influence of those security elements (ADP 3-90). It may be located as necessary to the front, flanks, or rear of a protected unit, facility, or location. Forces in a security area furnish information on an enemy force; delay, deceive, and disrupt that enemy force; and conduct counterreconnaissance.
Main Battle Area
5-17. The main battle area is the area where the commander intends to deploy the bulk of their unit to defeat an attacking enemy (FM 3-90). The defender’s major advantage is the ability to select the ground on which the battle takes place. The defender positions subordinate forces in mutually supporting positions in-depth to absorb enemy penetrations or canalize—a tactical mission task in which a unit restricts enemy movement to a narrow zone (FM 3-90)—them into prepared engagement area(s), defeating the enemy’s attack by concentrating the effects of overwhelming combat power. The natural defensive strength of positions determines the distribution of forces in relation to both frontage and depth. In addition, defending units typically employ field fortifications and obstacles to improve the terrain’s natural defensive strength.
Battle Handover Line
5-18. The battle handover line is a designated phase line where responsibility transitions from the stationary force to the moving force and vice versa (ADP 3-90). The common higher commander of the two forces establishes the battle handover line (BHL) after consulting with both forces. The stationary defender determines the exact location of the line. The BHL is forward of the forward edge of the battle area in the defense or the forward line of own troops (FLOT) in the offense and utilized during a passage of lines (forward or rearward).
Battle Positions
5-19. A battle position is a defensive location oriented on a likely enemy avenue of approach (ADP 3-90). Units as large as battalion task forces and as small as squads or sections use battle positions. They may occupy the topographical crest of a hill, a forward slope, a reverse slope, or a combination of all areas. The platoon leader selects positions based on terrain, enemy capabilities, and friendly capabilities. The leader can assign all or some subordinates battle positions within the AO.
5-20. There are five types of battle positions: primary, alternate, supplementary, subsequent, and strong point. When assigning battle positions within a company defense, the commander always designates the primary battle positions. Platoon leaders will generally define exactly where primary battle positions are location and designate alternate, supplementary, and subsequent positions as time and other resources permit, and if the terrain or situation requires them. (See figure 5-1 on page 5-6.) Before assigning a strong point, the commander ensures that the strong point force has sufficient time and resources to construct the position.
Figure 5-1. Primary, alternate, supplementary, and subsequent battle positions
5-21. A primary position is the position that covers the enemy’s most likely avenue of approach into the assigned area (FM 3-90). It is the best position from which to accomplish the defensive mission, such as the overwatch of an engagement area to prevent enemy penetration.
5-22. An alternate position is a defensive position that the commander assigns to a unit or weapon system for occupation when the primary position becomes untenable or unsuitable for carrying out the assigned task (FM 3-90). When established the alternate position covers the same area as the primary position. The correct positioning of an alternate position improves survivability by providing good cover and concealment for movement to the alternate position and back to the primary position. The position is located slightly to the front, flank, or rear of the primary battle position. The position may be positioned forward of the primary battle position during limited visibility operations. An alternate position is employed to supplement or support positions with weapons of limited range.
Note. Supplementary and subsequent positions are a way to achieve both flexibility and depth within the defense; however, they use must be planned for with displacement criteria and then rehearsed. All leaders should know when and why squads and/or the platoon will move to one of those positions.
5-23. A supplementary position is a defensive position located within a unit’s assigned area that provides the best sectors of fire and defensive terrain along an avenue of approach that is not the primary avenue where the enemy is expected to attack (FM 3-90). It is assigned when more than one avenue of approach runs into a unit’s AO. For example, an avenue of approach into a platoon’s AO from one of its flanks could require the company to direct its platoons to establish supplementary positions to allow the platoons to engage enemy forces traveling along an avenue. The platoon leader assigns supplementary positions when the platoon must cover more than one avenue of approach.
5-24. A subsequent position is a position that a unit expects to move to during the course of battle (FM 3-90). Subsequent positions can have primary, alternate, and supplementary positions associated with them.
5-25. A strong point is a heavily fortified battle position tied to a natural or reinforcing obstacle to create an anchor for the defense or to deny the enemy decisive or key terrain (ADP 3-90). A strong point implies retention of terrain to control key terrain and blocking, fixing, or canalizing enemy forces. Defending units require permission from the higher headquarters to withdraw from a strong point. All combat, maneuver enhancement, and sustainment assets within the strong point require fortified positions. In addition, extensive protective and tactical obstacles are required to provide an all-around defense. Primary positions cover the enemy’s most likely avenue of approach into the area. (See figure 5-2.)
Figure 5-2. Platoon strong point battle position
Note. A minimally effective strong point typically requires a 1-day effort from an engineer unit the same size as the unit defending the strong point. (See ATP 3-21.10 for additional information.)
Forward Edge Of The Battle Area
5-26. The forward edge of the battle area is the foremost limits of a series of areas in which ground combat units are deployed to coordinate fire support, the positioning of forces, or the maneuver of units, excluding areas in which covering or screening forces are operating (JP 3-09.3). When the defender defends forward in an area defense the unit employs the majority of its combat forces near the forward edge of the battle area.
Forward Line Of Own Troops
5-27. The forward line of own troops is a line which indicates the most forward positions of friendly forces in any kind of military operation at a specific time (FM 3-90). The FLOT normally identifies the forward location of covering or screening forces. In the defense, it may be beyond, at, or short of the forward edge of the battle area. It does not apply to small, long-range reconnaissance assets and similar stay-behind forces. Friendly forces forward of the FLOT may have a restrictive fire support coordination measure, such as a restrictive fire area, placed around them to prevent fratricide incidents.
Tactical Framework Of The Defense
5-28. Usually as part of a larger force, the Infantry rifle platoon conducts the defense performing several integrated and overlapping activities. As in the offense, defensive operations are typically executed in a four-step tactical framework. The framework is for discussion purposes only and is not the only way of executing defensive operations. Normally the first two steps are supporting efforts, while the finish step is the main effort. Follow through is usually a sequel or branch to the plan based upon the situation. These steps may not occur sequentially; they may occur simultaneously. These steps are—
- Find the enemy. Intel drives fires and maneuver.
- Fix the enemy. Prevent repositioning or reinforcement making them easier to destroy.
- Finish the enemy. Mass available combat power to accomplish the mission.
- Follow through. Defeat in detail, consolidate, reorganize, and transition.
Next Page : Section 2 – Common Defensive Planning Considerations