text: Defense
  positions. The commander assigned subordinate maneuver units an area of operations,based on the mission
  variables of METT-TC, to maximize decentralized execution empowering subordinate commanders to
  position battle positions within their assigned area of operations. At the same time, each subordinate
  commander addressed security requirements for the flanks of assigned area of operations by assigning
  responsibility to a subordinate element or organizing a security force or observation post(s) to accomplish
  that mission. The commander and subordinate commanders retained reserves to contain enemy penetrations
  between units and positions,to reinforce fires into an EA,or to help a portion of the security force or main
  body disengage from the enemy if required.
  7-146. Step 5. Plan and integrate obstacles. During the conduct of the area defense, countermobility (see
  ATP 3-90.8) planning is the primary concern of the assistant brigade engineer (known as ABE) under the
  supervision of the brigade engineer battalion commander and battalion and squadron engineer staff
  noncommissioned officers, in coordination with the BCT and battalion and squadron S-3, S-2, and fire
  support officers. (External to the BCT,engineer planners [division and corps] coordinate with the BCT ABE
  and brigade engineer battalion).The plan addresses how security area and MBAforces reinforce the natural
  defensive characteristics of the terrain with the employment of obstacles to block, disrupt, fix, and turn
  attacking enemy forces into planned EAs. Countermobility planning also includes the positioning of
  protective obstacles to prevent the enemy from closing with defensive battle positons within subordinate unit
  area defenses.
  7-147. Within the scenario, the IBCT commander’s concept for the employment of obstacles within the
  area defense (Infantry Battalion 2) forces the enemy to enter established EAs positioned where the
  commander intends to kill the enemy. To succeed,the battalion through the employment of obstacles and the
  static positioning of company and platoon battle positions control,stop,or canalize attacking enemy forces
  to counteract the enemy’s initiative. The commander,through dynamic actions of the battalion reserve,covers
  gaps between positions and takes advantage of available offensive opportunities such as a local attack or
  counterattack that do not risk the integrity of the defense (see figure 7-14on page 7-42).