Infantry Drills

3-118: Countermobility

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3-118. To succeed in the defense, the platoon leader integrates individual obstacles into direct and indirect fire plans, considering the intent for each obstacle group. (Refer to ATTP 3-90.4 for more information on countermobility in the defense.) Obstacles are normally constructed by engineers with help from the platoon. In the defense, the platoon or squad uses obstacles to:

  • Slow the enemy’s advance to give the platoon or squad more time to mass fires on him.
  • Protect defending units.
  • Canalize the enemy into places where he can easily be engaged.
  • Separate the enemy’s tanks from his infantry.
  • Strengthen areas that are lightly defended.

3-119. Obstacle intent includes the target and desired effect (clear task and purpose) and the relative location of the obstacle group. The purpose influences many aspects of the operation, from selecting and designing obstacle sites to conducting the defense. Normally, the company commander designates the purpose of an obstacle group. When employing obstacles, the leader considers the following principles:

  • Support the tactical plan. Obstacles supplement combat power, decrease the mobility of the enemy, and provide security for the platoon. While considering enemy avenues of approach, he also considers his own movement requirements, such as routes for resupply, withdrawal, counterattacks, patrols, and observation posts.
  • Tie in. He ties in his reinforcing obstacles with existing obstacles. He must also tie in the obstacle plan with his plans for fires.
  • Covered by observation and fire. He ensures that all obstacles are covered by observation and fire. This reduces the enemy’s ability to remove or breach the obstacles and increases the possibilities of placing fire on the enemy when he encounters the obstacle.
  • Constructed in-depth. He emplaces obstacles so that each new obstacle encountered by the enemy attrites the enemy force and causes a desired and controlled reaction. Proper use of obstacles in-depth wears the enemy down and significantly increases the overall effect.
  • Employed for surprise. An obvious pattern of obstacles would divulge locations of units and weapons. Friendly forces must avoid readily discernable, repetitive patterns.

Next: 3-120: Tactical Obstacles

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