text: Appendix A
  Figure A-31. Five kinds of battle positions
  A-64. The primary position is the position that covers the enemy’s most likely avenue of approach into
  the assigned area. It is the best position from which to accomplish the mission, such as cover an engagement
  area.
  A-65. An alternate position is a defensive position that the commander assigns to a unit or weapon
  system for occupation when the primary position becomes untenable or unsuitable for carrying out
  the assigned task. It covers the same area as the primary position. Commanders locate alternate positions so
  the occupants can continue to fulfill their original tasks, such as covering the same avenue of approach or
  engagement area as their primary positions. These positions increase the defenders’ survivability by allowing
  defenders to engage enemy forces from multiple positions. For example, a unit moves to its alternate positions
  when enemy forces bring suppressive fires on the primary position.
  A-66. A supplementary position is a defensive position located within a unit’s assigned area that
  provides the best sectors of fire and defensive terrain along an avenue of approach that is not the
  primary avenue where the enemy is expected to attack. For example, an avenue of approach into a unit’s
  assigned area from one of its flanks normally requires establishing supplementary positions to allow a unit
  or weapon system to engage enemy forces traveling along that avenue.
  A-67. A subsequent position is a position that a unit expects to move to during the course of battle. A
  planned and, to some extent, prepared location for a defense or delay that is behind the primary positions
  initially occupied for a defense. A defending unit may have a series of subsequent positions. Subsequent
  positions can be further organized into primary, alternate, and supplementary positions.
  A-68. A strong point is a heavily fortified battle position tied to a natural or reinforcing obstacle to create an
  anchor for the defense or to deny the enemy decisive or key terrain (ADP 3-90). Strong points require
  extensive engineer support to create obstacles and increase survivability efforts. This include providing all
  assets overhead protection, trenches, and other protective construction using both natural and man-made
  terrain. Commanders prepare a strong point for all around defense. Commanders also establish a strong point
  when anticipating that enemy actions will isolate a defending force retaining terrain critical to the defense.