text: Chapter 8
  is that area occupied by a unit’s security elements and includes the areas of influence of those security
  elements. The forward edge of the battle area is the foremost limits of a series of areas in which ground
  combat units are deployed to coordinate fire support, the positioning of forces, or the maneuver of units,
  excluding areas in which covering or screening forces are operating (JP 3-09.3). The forward line of own
  troops is a line that indicates the most forward positions of friendly forces in any kind of military operation
  at a specific time.
  Note. Throughout chapters 8 through 11, this publication will use the terms MBA, security area,
  forward edge of battle area, and FLOT as a visualization method of describing the assigned area
  for defending units.
  8-5. Units generally place their reserve where they can easily reinforce the main effort. However, the
  reserve may reinforce other priorities in the defense. Units use a reserve to—
  * Seize the initiative.
  * Destroy enemy forces.
  * Reinforce forces.
  * Block enemy avenues of approach.
  * Counterattack.
  CHARACTERISTICS OF THE DEFENSE
  8-6. Successful defenses share these characteristics:
  * Disruption.
  * Flexibility.
  * Maneuver.
  * Mass and concentration.
  * Depth.
  * Preparation.
  * Security.
  See ADP 3-90 for more information on the characteristics of the defense.
  TYPES OF DEFENSIVE OPERATIONS
  8-7. There are three types of defensive operations:
  * Area defense.
  * Mobile defense.
  * Retrograde.
  These three types of operations have significantly different concepts and present different problems. Units
  consider each independently when planning and executing the defense. Although the names of these types
  convey the overall aim of a selected operation, each type usually contains elements of the other and combines
  static and mobile elements. Table 8-1 depicts the symbols for an area defense and mobile defense. Table 8-2
  depicts the symbols for retrograde operations.