text: Chapter 9
  * Designating and preparing supplementary positions.
  * Designating hide positions and rehearsing movements to and from all fighting positions. (Units
  may place their vehicles in hide positions at any time while preparing the defensive position.)
  * Improving trafficability of projected counterattack routes.
  * Pre-stocking ammunition in positions where it can survive anticipated enemy preparation fires.
  * Positioning barrier material for constructing fighting positions and obstacles.
  * Rehearsing movements under daylight and limited-visibility conditions.
  * Establishing sleep and rest plans.
  * Continuing to improve the defense.
  9-43. Survivability positions enhance the strength of a defensive position by providing Soldiers and weapons
  systems with specified degrees of cover from enemy fires. Units initiate construction of survivability
  positions based on their priorities of work, and they continue to build and improve them until the last possible
  moment. The degree of overhead, frontal, and side protection provided varies with the location of the
  sheltered troops and enemy capabilities. Defending units improve communications routes throughout their
  defensive positions to ease movement of supplies and forces as time and resources allow. Communications
  routes are particularly important for reserves. Units establish tactical communications with their various
  subordinate elements and offsite antennas to reduce their electromagnetic signature.
  9-44. Defending units rehearse how they move to and from primary, alternate, supplementary, and sequential
  positions. These rehearsals establish the time necessary to conduct these movements under different
  environmental conditions. Units modify their existing defensive plans based on the results of these rehearsals
  and changes in the mission variables. They check that the routes taken during these rehearsals do not show
  obvious signs of heavy use. These steps can include the conduct of only dismounted rehearsals, only moving
  one vehicle per platoon, and taking steps to eliminate signs of movement such as sweeping snow back over
  the tracks made during the rehearsal.
  9-45. Commanders ensure close coordination among their subordinates. One way to do this during the
  preparation phase is for them to take their subordinate commanders to vantage points in the MBA if such
  sites are available. They can conduct rehearsals and finalize coordination from those positions. This technique
  also helps commanders transmit their intent and share their situational understanding.
  9-46. The location, composition, and movement of echelon reserves are typically essential elements of
  friendly information. Other typical essential elements of friendly information in the defense include location
  of main obstacle belts, location of critical countermobility assets, indirect fire assets, and supply points.
  Enemy reconnaissance focuses on finding these reserves and reporting when and where they commit.
  9-47. Units integrate sustainment into their maneuver rehearsals to verify that routes for support do not cross
  or conflict with routes used by their reserves or other maneuver elements. They balance the use of
  ammunition and other supply caches against their ability to secure those caches. Units also ensure the
  availability of alternate lines of communications and MSRs to support their contingency plans and changes
  in tactical situations.
  9-48. Units ensure the integration of available combat enablers into their plans. During this phase,
  commanders verify that their subordinate commanders and other leaders have a shared understanding of their
  plans and can execute them with minimal guidance. One technique that commanders use to ensure
  subordinate understanding is the receipt of backbriefs from their subordinates after they issue their orders.
  EXECUTION CONSIDERATIONS FOR AN AREA DEFENSE
  9-49. In an area defense, units use various techniques and procedures to accomplish their missions.
  Defending forces repeatedly seek to force the enemy to maneuver into engagement areas where they can
  target them. Defending forces operate mainly from prepared, protected positions to concentrate combat power
  against attempted enemy breakthroughs and flanking movements. Units use their mobile forces to cover gaps
  between their defensive positions, reinforce those positions as necessary, and counterattack to seal
  penetrations or block enemy attempts at flanking movements. Figure 9-6 illustrates control measures that
  units can use when mixing static and mobile elements in an area defense.