text: Area Defense
  other location. Units may employ fire support assets and local counterattacks by forces already defending to
  destroy, disrupt, or attrit enemy penetrations, thus avoiding the need to commit reserves. Units launch their
  counterattacks when enemy forces present their flanks, overextend, or the enemy forces’ momentum
  dissipates. Units can target counterattacks to isolate and destroy selected enemy forces within the MBA once
  they can identify the flanks of the enemy force’s main effort.
  9-98. Sometimes commanders may determine that their reserves are unable to conduct successful
  counterattacks. Units use their available resources to block, contain, or delay enemy forces in this situation.
  This gains time for the employment of higher echelon reserves. Commanders and staffs adjust their existing
  defensive plans to integrate these high-echelon reserves into their defensive and counterattack schemes. Units
  adjust boundaries and designate additional BPs for occupation. They plan the routes units will use and any
  necessary adjustments to existing command and support relationships. They can speed the process of
  positioning and moving these reserves by designating routes, allocating mobility assets, and providing traffic
  control personnel and guides at designated contact points to lead and brief them on the situation. Units employ
  maneuver battalion scouts, military police, and cavalry units to provide traffic control during the movement
  of these reserves because they have the combat power to protect themselves from those small enemy forces
  that units may encounter in this situation.
  Follow Through
  9-99. Defensive actions aim to retain terrain and create conditions for a counteroffensive that regains the
  initiative. The area defense does this by causing enemy forces to sustain unacceptable losses before reaching
  their objectives.
  9-100. Upon defeating the enemy attack, commanders have a decision to make. They can consolidate,
  reorganize, and begin the counterattack. They can consolidate and reorganize and prepare to defend again. If
  they are unable to defeat the enemy attack, they need to transition to a retrograde. Any decision to withdraw
  must account for the current situation in adjacent defensive areas. Only the higher echelon commander who
  ordered the defense can designate a new FEBA or authorize a retrograde operation. No matter what option is
  chosen, units must continue to conduct MEDEVAC and CASEVAC, battle damage assessment and repair,
  detainee operations, and begin setting conditions for the branch or sequel to their defense.
  REVERSE SLOPE DEFENSE
  9-101. For a reverse slope defense, units organize their defense on the portion of a terrain feature or slope
  with a topographical crest that masks the main defensive positions from enemy observation and direct fire.
  All or part of the defending force may employ this technique. It is generally useful at lower tactical echelons,
  such as battalion and below.
  9-102. Units base a successful reverse slope defense on denying enemy forces the topographical crest.
  Although a defender may not occupy a crest in strength, controlling the crest by fire is essential for success.
  Controlling the crest reduces the effects of indirect fire (mortar, artillery, and close air support) and draws
  the battle into small-arms range. Units use a reverse slope defense to provide a defending force an opportunity
  to gain surprise. Their goal is to make enemy forces commit forces against the forward slope of the defense,
  causing enemy forces to attack in an uncoordinated fashion across the exposed topographical crest. Firing
  from covered and concealed positions throughout the battle area, the defending force maintains a distinct
  advantage over the exposed enemy forces and canalizes them through unfamiliar terrain into engagement
  areas Figure 9-12 on page 9-22 shows the terminology associated with the reverse slope defense.