text: Chapter 8
  AREA DEFENSE
  8-60. Area defense is a type of defensive operation that concentrates on denying enemy forces access to
  designated terrain for a specific time rather than destroying the enemy outright (ADP 3-90). Area defense
  can occur at the tactical and operational levels of warfare. The area defense focuses on retaining terrain where
  the bulk of a defending force positions itself in mutually supporting, prepared positions. Units maintain their
  positions and control the terrain between these positions. The operation focuses fires into engagement areas,
  possibly supplemented by a counterattack. Commanders can use their reserve to reinforce fires, add depth,
  block, or restore a position by counterattack; seize the initiative; and destroy enemy forces. Units at all
  echelons can conduct an area defense. (See FM 3-90 for the advantages and disadvantages of using a defense
  in depth and a forward defense during the conduct of an area defense.)
  MOBILE DEFENSE
  8-61. Mobile defense is a type of defensive operation that concentrates on the destruction or defeat of the
  enemy through a decisive attack by a striking force (ADP 3-90). Mobile defense is more often associated
  with the operational level of warfare. The mobile defense focuses on defeating or destroying an enemy by
  allowing enemy forces to advance to a point where they are exposed to a decisive counterattack by a striking
  force—a dedicated counterattack force in a mobile defense constituted with the bulk of available combat
  power (ADP 3-90). A fixing force—a force designated to supplement the striking force by preventing the
  enemy from moving from a specific area for a specific time (ADP 3-90)—supplements the striking force by
  holding attacking enemy forces in position to help channel attacking enemy forces into ambush areas and to
  retain areas from which to launch the striking force.
  8-62. A mobile defense requires an AO with considerable depth. Commanders shape their battlefields,
  causing an enemy force to overextend its lines of communications, expose its flanks, and dissipate its combat
  power. Commanders move friendly forces around and behind an enemy force to cut off and destroy them. A
  division or higher echelon normally executes a mobile defense. BCTs and maneuver battalions participate in
  a mobile defense as part of a striking force or fixing force.
  RETROGRADE
  8-63. Retrograde is a type of defensive operation that involves organized movement away from the enemy
  (ADP 3-90). A retrograde can take place at the tactical or operational levels of warfare. An enemy may force
  these operations, or a commander may execute them voluntarily. The higher echelon commander of a force
  executing a retrograde must approve the retrograde before its initiation. A retrograde is a transitional
  operation. It is not conducted in isolation. It is always part of a larger scheme of maneuver designed to regain
  the initiative and defeat the enemy.
  8-64. The following are the three forms of the retrograde:
  ⚫ Delay is when a force under pressure trades space for time by slowing down the enemy’s
  momentum and inflicting maximum damage on enemy forces without becoming decisively
  engaged (ADP 3-90). In delays, units yield ground to gain time while retaining flexibility and
  freedom of action to inflict the maximum damage on an enemy.
  ⚫ Withdraw is to disengage from an enemy force and move in a direction away from the enemy
  (ADP 3-90). Withdrawing units, whether all or part of a committed force, voluntarily disengage
  from an enemy to preserve the force or release it for a new mission.
  ⚫ Retirement is when a force out of contact moves away from the enemy (ADP 3-90).
  8-65. In each form of retrograde, a force not in contact with an enemy moves to another location, normally
  by a tactical road march. In all retrograde operations, firm control of friendly maneuver elements is a
  prerequisite for success.