text: Chapter 8
  attacking enemy forces in position, to turn attacking enemy forces into ambush areas, and to retain
  areas from which to launch the striking force.
  * The striking force is a dedicated counterattack force in a mobile defense constituted with the bulk
  of available combat power (ADP 3-90).
  8-10. A mobile defense requires assigned areas of considerable depth. Units shape the battlefield causing an
  enemy force to overextend its LOCs, expose its flanks, and dissipate its combat power. Likewise, they must
  be able to move their forces into a position where they can defeat the attacking force. Divisions and larger
  formations normally execute mobile defenses. In limited circumstances a BCT can execute a mobile defense
  unilaterally. (See Chapter 10 for more information on mobile defense.)
  RETROGRADE
  8-11. A retrograde is a type of defensive operation involving organized movement away from the enemy
  (ADP 3-90). An enemy force may compel these operations, or units may execute them voluntarily. In either
  case, the higher echelon headquarters executing the retrograde must approve the operation before its
  initiation. The retrograde is not conducted in isolation; it is a transitional operation. It is part of a larger
  maneuver scheme designed to preserve combat power in order to regain the initiative in future operations.
  The three variations of the retrograde are delay, withdraw, and retirement. (See Chapter 11 for more
  information on retrograde.)
  COMMON DEFENSIVE CONTROL MEASURES
  8-12. Paragraphs A-63 through A-88 define common control measures specific to defensive operations.
  Units use the minimum control measures required to complete their missions while providing subordinates
  the flexibility needed to respond to changes in the situation.
  8-13. Units control the defense by using control measures that provide the flexibility needed to respond to
  changes in the situation and allow them to concentrate combat power at the decisive point. Common
  defensive control measures are:
  * Engagement area (EA).
  * Battle position (BP).
  * Battle handover line (BHL).
  * Named area of interest (NAI).
  * Target areas of interest (TAI).
  * Fire support coordination measures (FSCMs).
  * Disengagement line.
  * Phase lines.
  COMMON DEFENSIVE PLANNING CONSIDERATIONS
  8-14. A defense is more effective when there is adequate time to thoroughly plan and prepare defensive
  positions. Lack of preparation time may cause units to maintain a larger reserve force or accept greater risks
  than usual. All units must be capable of mounting a defense with minimal preparation, but a strong defense
  takes time to organize and prepare. Time is always a critical factor so units must establish clear priorities of
  work to provide focus for critical capabilities such as countermobility assets. If an enemy attack does not
  take place at the predicted time, units use the additional time to continue improving their position. Units
  increase the effectiveness of the security area, establish additional fighting positions (alternate,
  supplementary, and subsequent), refine the defensive plan (to include branches and sequels), conduct
  defensive rehearsals, and maintain vehicles and personnel.
  8-15. To gain time to organize a defense, units may order the security force to conduct a delay while the
  main body disengages and moves to more advantageous positions. The security force must know how long
  it needs to delay enemy forces for the main body so that it can task-organize and prepare its defense. Security
  forces are also given additional tasks to disrupt the enemy’s attack and attrit key enemy formations or