text: Area Defense
  Planning a Perimeter Defense
  9-73. Defending units position their forces and plan fire and movement so they can respond to the widest
  possible range of enemy actions. Defending commanders, assisted by their staffs, prepare plans, including
  counterattack plans. Units rehearse, evaluate, and revise their plans as needed. The availability of landing
  and drop zones protected from enemy observation and fire is a major consideration when selecting and
  organizing the perimeter defense. Units must emphasize supply economy and protect existing supply stocks
  since aerial resupply is vulnerable to weather and enemy fires. Commanders consider the fundamentals of an
  area defense in paragraphs 9-18 through 9-39 when planning a perimeter defense.
  Figure 9-11. Example perimeter defense control measures
  9-74. The mission variables considered when commanders and staffs developed their counterattack plans as
  branches or sequels to their defensive plans may not correspond exactly with the situation when the moment
  comes to execute those counterattacks. Units reassess and revise their counterattack plans based on their
  revised situational understanding as their defenses unfold. This revised understanding results from an updated
  common operational picture as new intelligence and combat information becomes available to answer these
  questions:
  * Is a counterattack feasible or should commanders use the reserve to contain enemy successes?
  * When and where should defending forces counterattack?
  * What parts of the defending force should counterattack?
  * What should defending forces block or contain in the case of successful enemy penetrations?
  * Is there enough time to complete the counterattack before the arrival of enemy follow-on forces?
  * Can commanders conduct their counterattack using only available fires or must ground maneuver
  forces be committed?