Infantry Drills

3-146: Defense of the Linear Obstacle

Previous: Section III: Forms of the Defense

3-146. A platoon leader may conduct either an area or mobile defense along or behind a linear obstacle. The Infantry leader normally prefers an area defense because it accepts less risk by not allowing the enemy to cross the obstacle. Linear obstacles such as mountain ranges or river lines generally favor a forward defense. It is extremely difficult to deploy in strength along the entire length of a linear obstacle. The defending leader must conduct economy of force measures in some areas.

3-147. Within an area defense, the leader’s use of a defense in-depth accepts the possibility the enemy may force a crossing at a given point. The depth of the defense should prevent the enemy from rapidly exploiting its success. It also defuses the enemy‘s combat power by forcing the enemy to contain bypassed friendly defensive positions in addition to continuing to attack positions in greater depth.

3-148. This form of defense may be used when defensible terrain is available in the forward portion of the platoon’s area of operation, or to take advantage of a major linear natural obstacle. It also is used when the enemy is mainly Infantry; the platoon conducts a security mission such as counter infiltration, or as directed by company. This technique allows interlocking and overlapping observation and fields of fire across the platoon’s front. (See figure 3-12.) The bulk of the platoon’s combat power is well forward. Sufficient resources must be available to provide adequate combat power to detect and stop an attack. The platoon relies on fighting from well-prepared mutually supporting positions. It uses a high volume of direct and indirect fires to stop the attacks. The main concern when fighting this form of defense is the lack of flexibility and the difficulty of both seizing the initiative and seeking out enemy weaknesses. Obstacles, indirect fires, and contingency plans are vital to this maneuver. The platoon depends upon surprise, well-prepared positions, and deadly accurate fires to defeat the enemy. The reserve is usually small, perhaps a squad.

Figure 3-12. Platoon defense of a linear obstacle

3-149. Minefields and other obstacles are positioned and covered by fire to slow the enemy and inflict casualties. Engaging the enemy at long range by supporting fires (CAS, attack helicopters, and field artillery) disrupts the momentum of his the attack. Use fires from mortars, machine guns, and small arms as he comes into range. If the defense is penetrated, block the advance with the reserve and shift fire from the forward squads onto the enemy flanks. Then, counterattack with the platoon reserve or the least committed squad with intense fires. The purpose is to destroy isolated or weakened enemy forces and
regain key terrain.

3-150. The counterreconnaissance effort is critical when fighting to deny the enemy the locations of the platoon’s forward positions. If the enemy locates the forward positions, he will concentrate combat power where he desires while fixing the rest of the platoon to prevent their maneuver to disrupt his attack. This effort might be enhanced by initially occupying and fighting from alternate positions forward of the primary positions. This tactic enhances the security mission and deceives the enemy reconnaissance that may get through the security force.

Next: 3-151: Perimeter Defense

Go Back To: U.S. Army FM 3-21.8: The Infantry Rifle Platoon and Squad