text: Chapter 8
  defiles, rivers, thick woods, swamps, cliffs, canals, built-up areas, and reverse slopes. Effective defensive
  positions in the MBA use natural and man-made obstacles. Units may choose to shape the battlefield by
  defending in one area to deny terrain to enemy forces while delaying in another area to deceive the enemy
  into believing that the attacking enemy force has achieved success.
  8-50. Defending units use key terrain to impede an enemy force’s movement and place overwatching
  elements in positions to provide early warning and engage enemy forces with indirect fires. These positions
  can be located forward of the topographical crest and on the flanks of positions in a valley or depression.
  Defending units select terrain that allows the massing of friendly fires and forces the enemy to commit its
  forces piecemeal into friendly engagement areas. This exposes portions of the enemy force to destruction
  without giving up the advantages of fighting from protected positions. Examples of key terrain include terrain
  that permits the defending force to cover a major obstacle system by fire and important road junctions or
  choke points that affect troop movements.
  8-51. Units determine the probable combat power ratios the defenders will face and establish positions
  accordingly. Once defending units arrive at acceptable force ratios—or the degree of risk is clear—they
  allocate available forces and begin planning engagement areas. They determine where to engage enemy
  forces on each enemy avenue of approach. Defending units array forces on those avenues of approach and
  establish engagement areas using obstacles and fires to canalize enemy forces into them. They take actions
  to increase the kill probabilities of various weapons systems at different ranges. This includes establishing
  range markers for direct fire weapons, confirming the zero on weapons, and clearing obstacles that might
  impede wire-guided munitions.
  8-52. The seven steps of engagement area development include the following:
  * Identify likely enemy avenues of approach.
  * Identify most likely enemy course of action.
  * Determine where to kill the enemy.
  * Position subordinate forces and weapons systems.
  * Plan and integrate obstacles.
  * Plan and integrate fires.
  * Rehearse the execution of operations within the engagement area.
  For more information on engagement area development see ATP 3-21.10.
  8-53. Generally, defending forces have the advantage of preparing the terrain by reinforcing natural
  obstacles, fortifying positions, and rehearsing operations. First, they prepare the ground to force the
  piecemeal commitment of the enemy and its subsequent defeat in detail. Second, they identify good locations
  for engagement areas along the enemy’s expected avenue of approach, such as in open areas dominated by
  terrain that offers adequate cover and concealment for the defending forces. Defending forces use natural and
  reinforcing obstacles to compel the enemy into these prepared engagement areas. Units employ and
  continuously strengthen obstacles and fortifications to improve the natural defensive strength of a position,
  which has a direct bearing on the distribution of forces, frontages, and depth of the defense. Lastly, defending
  forces rehearse defensive operations.
  8-54. Examples of terrain features that favor the defense include—
  * A series of parallel ridges across the line of hostile advance.
  * Unfordable streams, swamps, lakes, and other obstacles on the front and flanks.
  * High ground with good observation and long-range fields of fire.
  * Concealed movement routes immediately behind defensive positions.
  * A limited road network in front of the line of contact to confine enemy forces to predictable
  avenues of approach.
  * A good road network behind the line of contact that allows a defending unit to reposition forces
  as the battle progresses.
  8-55. The opposite of terrain conditions listed in paragraph 8-54 degrades a force’s ability to conduct
  defensive operations. For example, terrain with a limited road network that canalizes the defending force
  allows enemy forces to predict its movement and take steps to interdict that movement.