text: Chapter 9
  significantly affects the overall effectiveness of the area defense. Units prepare to adjust their defensive
  dispositions to meet changes in the enemy’s dispositions to maintain that cohesion.
  9-25. The area defense requires units in defensive positions to accomplish their mission independently or in
  combination by defeating enemy forces by fire, absorbing the strength of the attack within their positions, or
  destroying enemy forces with local counterattacks. Units combine the advantages of fighting from prepared
  positions, obstacles, planned fires, and local counterattacks to isolate and overwhelm selected enemy
  formations. They rapidly shift the purpose and location of their main effort throughout their assigned areas
  as conditions change. Commanders may have to reposition defending units within their defensive positions
  or reposition between terrain features to mass the effects of overwhelming fires against attacking enemy
  units. The defensive plans designate axes of advance and routes for the commitment or movement of their
  reserves, or the forward or rearward passage of one unit through another. Those plans identify air axes for
  aerial maneuver by attack aviation elements, air assault units, or fixed-wing aircraft. Their operations
  processes identify decision points associated with the initiation of these counterattacks, the repositioning of
  forces, and other actions.
  9-26. The capability to reposition relies on defending forces having tactical mobility. Defending forces stay
  in their prepared positions and accept the possibility of becoming decisively engaged if they lack this mobility
  advantage.
  9-27. Commanders assigning defensive missions define their defended areas. They have to accept gaps and
  conduct noncontiguous operations when defending on broad fronts with minimal forces. This results in a
  noncontiguous FLOT. Defending shallow assigned areas requires units to operate well forward with a
  corresponding reduction in their flexibility.
  9-28. The ideal area defense is one where effective mutual support exists throughout the width and depth of
  the defender’s tactical positions. Units organize and occupy defensive positions based on their natural
  defensive strength. Defending units maintain tactical integrity within their defensive areas. Units conducting
  an area defense normally address flank security requirements by assigning those responsibilities to
  subordinate elements or organizing a separate security force to perform that task.
  9-29. Units typically have two methods for the placement of their positions when conducting an area defense:
  defense in depth and forward defense. A higher echelon commander may dictate the method to their
  subordinates or subordinates may retain the flexibility to choose the method of an area defense. These two
  methods are not exclusionary. Part of a defending unit can conduct a forward defense while the other part
  conducts a defense in depth.
  Defense in Depth
  9-30. Units normally prefer to perform a defense in depth. Forces defending in depth absorb the momentum
  of enemy attacks by making enemy forces attack repeatedly through a series of mutually supporting positions.
  Building these positions requires significant time and engineer support to increase the survivability and
  countermobility of those positions. Depth gives fire support assets time to deliver effects on multiple
  locations against selected elements of the attacking enemy force. Depth provides more reaction time for
  defending forces to respond by repositioning or counterattacking. Units continuously employ their
  information collection assets to gather additional information about the attacking enemy’s intentions and
  capabilities between the time combat starts and the time the enemy commits to a COA. Depth reduces the
  risk of enemy forces rapidly penetrating the MBA along unexpected directions.
  9-31. Units also employ a defense in depth when enemy forces can employ large quantities of indirect fires.
  Units disperse their forces throughout their assigned area when conducting a defense in depth. They take area
  damage control measures to reduce the effects of these munitions and weapons on defending friendly forces,
  and they deny enemy forces lucrative targets. The degree of dispersal adopted by defending forces is a
  function of the enemy and friendly forces’ capabilities as well as the terrain to rapidly concentrate combat
  power at decisive points.
  9-32. Commanders can position their defending units in successive layers of BPs along likely enemy avenues
  of approach when conducting a defense in depth. (Figure 9-4 is a sketch illustrating this concept. It depicts a