text: Defense
  commander and staff must look closely for key and decisive terrain,EAs,choke points,intervisibility lines,
  and reverse slope opportunities to take full advantage of the BCT’s capabilities to mass firepower to support
  defensive maneuvers.
  7-31. The BCT commander must determine any potential gaps between units once maneuver units are
  assigned area of operations. The BCT should plan to cover any gaps with reconnaissance and security forces
  and surveillance assets. The BCT must plan local counterattacks to isolate and destroy any enemy that
  penetrates a gap in the area of operations. The commander should alsoplan to reposition units not in contact
  to mass the effects of combat power against an attacking enemy.
  7-32. The BCT commander identifies EAs(see paragraph 7-130) to contain or destroy the enemy force with
  the massed effect of all available weapons and supporting systems with the assignment of area of operations.
  The commander determines the size and shape of the EA by the visibility of the weapons systems in their
  firing positions and the maximum range of those weapons. The commander designates EAs to cover each
  enemy avenue of approach into the area of operations. Elements,deliberately left behind or inserted through
  infiltration or helicopter,can report and call in fires on an approaching enemy.
  7-33. The BCT combines fires,defensive positions,countermobility obstacles,and counterattacks to disrupt
  the enemy’s attack and break the enemy’s will. The BCT must disrupt the synchronization of the enemy’s
  operation to counter the enemy’s initiative,prevent the enemy’s concentrating combat power against a part
  ofthe defense,and force the enemy where the commander wants the enemy to go. The commander causes
  disruption defeating or misleading the enemy’s reconnaissance forces, impeding maneuver, disrupting
  reserve,neutralizing fire support,and interrupting command and control.
  7-34. Defensive techniques vary with circumstances,but all defensive concepts of operation aim to spoil the
  attacker’s synchronization. Strong security forces to defeat enemy reconnaissance,phony initial positions or
  dummy positions, and obstacles are some of the measures used to increase security in the defense.
  Repositioning forces, aggressive local protection measures, and employment of roadblocks and ambushes
  combine to disrupt the threat of an attack. Counterattack,counterbattery fires,obstacles,and retention of key
  or decisive terrain prevent the enemy from concentrating overwhelming strength against portions of the
  defense.
  7-35. The information environment supports the commander’s mission and desired end state using
  information-related capabilities, techniques, or activities. These capabilities include, but are not limited to,
  public affairs operations, psychological operations (PSYOP), combat camera, Soldier and leader
  engagement,civil affairs operations,civil and cultural considerations,operations security,military deception,
  and CEMA. CEMA (see chapter 4) at the BCT level include cyberspace operations, EW, and spectrum
  management operations. (SeeFM 3-13 and FM 3-12 for additional information.)
  7-36. The BCT commander considers mutual support when task organizing forces, assigning areas of
  operations, and positioning units. Mutual support is that support which units render each other against an
  enemy, because of their assigned tasks, their position relative to each other and to the enemy, and their
  inherent capabilities. Mutual support has two aspects—supporting range and supporting distance.
  7-37. Supporting range is the distance one unit may be geographically separated from a second unit yet
  remain within the maximum range of the second unit’s weapons systems. Mutual support exists when
  positions and units are in supporting range by direct or indirect fires, thus preventing the enemy from
  attacking one position without subjecting themselves to fire from one or more adjacent positions. Supporting
  distance is the distance between two units that can be traveled in time for one to come to the aid of the other
  and prevent its defeat by an enemy or ensure it retainscontrol of a civil situation. When friendly forces are
  static,supporting range equals supporting distance.
  7-38. Mutual support increases the strength of all defensive positions, prevents defeat in detail, and helps
  prevent infiltration between positions. Tactical positions achieve the maximum degree of mutual support
  between them when they are located to observe or monitor the ground between them or conduct patrols to
  prevent any enemy infiltration. At night or during periods of limited visibility,the commander may position
  small tactical units closer together to retain the advantages of mutual support. Unit leaders must coordinate
  the nature and extent of their mutual support.