text: Chapter 7
  counterattack against the flank or rear of an attacking enemy. The reserve gives the commander the flexibility
  to exploit success or to deal with a tactical setback.
  7-120. The commander positions the reserve to respond quickly to unanticipated missions. The commander
  determines the reserve’s size and position based on accurate knowledge about the enemy and whether the
  terrain can accommodate multiple enemy COAs. When the BCT has accurate knowledge about the enemy
  and the enemy’s maneuver options are limited,the BCT can maintain a smaller reserve. If knowledge about
  theenemy is limited and the terrain allows the enemy multiple COAs,then the BCT needs a larger reserve
  positioned deeper into the area of operations. (SeeFM 3-90-1 for additional information.)
  Sustainment
  7-121. The sustainment mission in an area defense requires a balance among establishing forward supply
  stocks of ammunition, barrier material, and other supplies in sufficient amounts, and having the ability to
  move the supplies in conjunction with enemy advances. Proper forecasting of supply and support
  requirements is important to the success of the area defense. The location of sustainment units within the
  support area is METT-TC dependent. (See chapter 9.)
  PLANNING AN AREA DEFENSE
  7-122. An area defense requires detailed planning and extensive coordination. In the defense,synchronizing
  and integrating the BCTs combat and supporting capabilities enables a commander to apply overwhelming
  combat power against selected advancing enemy forces. A successful defense depends on knowing and
  understanding the enemy and its capabilities. The commander’s situational understanding is critical in
  establishing the conditions that initiate the defensive action. As the situation develops, the commander
  reassesses the plan based on a revised situational understanding that results from an updated common
  operational picture (COP) as new intelligence and combat information becomes available. In planning an
  area defense,the commander may choose between two forms of defensive maneuver—a defense in-depth or
  a forward defense.
  Understanding
  7-123. The BCT commander considers the mission variables of METT-TC to determine how to concentrate
  efforts and economize forcesin order to accomplish the mission. A detailed terrain analysis may be the most
  important process the BCT commander and staff complete. A successful defense relies on a complete
  understanding of terrain to determine likely enemy COAsand the best positioning of BCT assets to counter
  them.
  7-124. The commander must understand the situation in-depth, develop the situation through action, and
  constantly reassess the situation to keep pace with the engagement. Defending forces must gain and maintain
  contact with the enemy to observe, assess, and interpret enemy reactions and the ensuing opportunities or
  threats to friendly forces, populations, or the mission. The commander must establish priority intelligence
  requirements to enable information collection through reconnaissance,surveillance,intelligence operations,
  and security operations to develop situational understanding.
  7-125. Enemy forces counter friendly information collection efforts to prevent the BCT from gaining
  information. Enemy forces use other countermeasures such as dispersion, concealment, deception, and
  intermingling with the population to limit the BCT’s ability to develop the situation out of contact.
  Reconnaissance and security forces (see chapter 5) fill in the gaps in commanders’ understanding of the
  situation. Fighting for understanding and identifying opportunities to seize,retain,and exploit the initiative
  requires combined arms capabilities, access to joint capabilities, specialized training, and employing
  combinations of manned and unmanned air and ground systems.
  Forms of Defensive Maneuver
  7-126. The BCT commander may choose between two defensive maneuver forms when planning an area
  defense, a defense in-depth, or a forward defense. The commander usually selects the form of defensive
  maneuver,but the higher headquarters’commander may define the general defensive scheme for the BCT.
  These two deployment choices are not totally exclusionary. Part of a defending commander’s unit can