text: The Defense
  Table 8-1. Defensive operations symbols
  Type of Defense Symbol
  Area defense
  Mobile defense
  Table 8-2. Retrograde task symbols
  Retrograde Task Symbol
  Delay
  Withdraw
  Retirement
  AREA DEFENSE
  8-8. An 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). The purpose of
  an area defense is to retain the terrain where the bulk of the defending force positions itself in mutually
  supporting prepared positions. Units maintain their positions and control the terrain between these positions.
  The main effort focuses fires into engagement areas, possibly supplemented by a counterattack. Units at all
  echelons can conduct an area defense. They may use an area defense to transition to offensive operations,
  retrograde, or stability operations. The variations of an area defense are defense of linear obstacle, perimeter
  defense, and reverse slope defense. (See Chapter 9 for more information on area defense.)
  MOBILE DEFENSE
  8-9. A 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). The mobile defense focuses on defeating or
  destroying enemy forces by allowing them to advance to a point where they are exposed to a decisive
  counterattack. A mobile defense includes a fixing force and a striking force:
  * A fixing force is 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). Units use the fixing force to hold