text: Defense
  7-11. Concealment and deception must mask the concentrating forces since concentration increases the risk
  level of large losses from enemy fires. The strategy is to concentrate the effects of the forces,not to physically
  concentrate the forces themselves. Defending units use engagement areas (EAs) to concentrate combat power
  from mutually supporting positions. Reconnaissance, surveillance, and security operations, organic and
  nonorganic to the BCT, are vital to gaining the information and time needed to concentrate the forces and
  fires of the BCT.
  OPERATIONS IN DEPTH
  7-12. Operations in deptharethe simultaneous application ofcombat power throughout an area of operations
  (ADP 3-90). Integration of all combat power throughout the area of operations,as well as the BCT’s area of
  influence and area of interest,improves the chances for success while minimizing friendly casualties. Quick,
  violent,and simultaneous action throughout the depth of the BCT’s area of operations can hurt,confuse,and
  even paralyze an enemy force when most exposed and vulnerable. Such actions weaken the enemy’s morale
  and do not allow any early successesto build their confidence. Operations indepth prevent the enemy from
  gaining momentum in the attack. Synchronization of actions within the division’s operational framework
  facilitates mission success.
  7-13. Alternate and supplementary positions, combat outposts,observation posts, and mutually supporting
  strong points extend the depth of the defense. The commander plans fires throughout the defensive area up
  to the maximum range of available weapons. Fire support units and observers move and reposition to
  maintain contact with enemy forces and observe TAIsin-depth as the battle develops. The commander plans
  for the emplacement of obstacles around critical locations to disrupt the enemy’s most dangerous and most
  likely COAs.
  PREPARATION
  7-14. The commander must be familiar with the enemy’s abilities and limitations to prepare the defense
  properly. The enemy’s abilities and limitations include their organization, offensive doctrine (tactics,
  techniques, and procedures), weapons systems, and equipment. Collection means (reconnaissance,
  surveillance, security operations, and intelligence operations) inform the commander and staff to enable
  understanding and multiply the effectiveness of the defense.
  7-15. The commander analyzes the terrain in detail from all perspectives and then verifies on the ground to
  select EAsand positions that allow for the massing of fires and the concentration of forces on likely enemy
  avenues of approach. Emphasis is on preparing and concealing positions,routes,obstacles,logistical support,
  and command and control facilities and networks. The commander plans,coordinates,and prepares military
  deceptions and uses rehearsals to ensure staffs and subordinates understand the concept of operations and
  commander’s intent.
  7-16. During preparation,aerial (manned and unmanned) reconnaissance and surveillance collection efforts
  (internal and external to the BCT) complement ground efforts by increasing speed and depth with which
  reconnaissance can be conducted over an area. Ground reconnaissance and security forces employ, and
  supplies are pre-positioned. Counterattack plans to support the defense and to place the BCT on the offense
  are key to retaining the initiative. Counterattack routes must be reconnoitered, improved, secured, and
  rehearsed. Defensive preparations within the main battle area (MBA) continue in-depth even as close
  engagement begins.
  SECURITY
  7-17. The BCT commander establishes security areas forward of the MBA, on the flanks, and within the
  BCT’s support area to protect the force while in the defense. Security operations forward of the MBA
  normally include screen, guard, and cover. The presence of a security force forward of the MBA does not
  relieve the MBA units from their own security responsibilities (area security and local security tasks). All
  units must maintain security,for example civil reconnaissance and security patrolling,within assigned areas
  and contribute to counterreconnaissance.