text: Countermobility
  17-31. Indirect fires and long-range direct fires are used to cause the enemy to change from a march
  formation to a prebattle or attack formation, resulting in reduced closure speed and increased time to engage
  the enemy in the engagement area. Generally, indirect fires alone will not force an enemy to deploy except
  when dismounted.
  17-32. Units plan suppression and neutralization indirect fire targets or groups on the obstacles in a disrupt
  obstacle group. Indirect fires are used with the obstacles to slow the part of the enemy force that makes
  contact with the obstacles. Units also use every means available to disrupt enemy command and control
  throughout the enemy formation. Units use electromagnetic warfare, obscuration, and indirect fires to disrupt
  the decision cycle of the enemy and increase the direct fire window on the unimpeded part of the enemy
  force.
  17-33. Units use target reference points to mass direct fires against the part of the enemy formation that is
  not impeded by obstacles and indirect fires. Units do not execute those fires until the enemy force separates
  from its parent formation. They use direct fire weapons that can deliver a lethal initial volley of fire. A quick
  volley is critical if the enemy has good command and control and can react quickly to the disruption of its
  formation. Disengagement criteria are also a consideration in weapons selection. If units plan a short
  engagement, they choose a weapon system that can fire and maneuver without becoming decisively engaged.
  If they expect a long engagement, they select a weapon system that can sustain rapid fire with sufficient
  survivability to support the engagement.
  17-34. Units plan fire control measures that allow for the shift of direct or indirect fires to the enemy that
  are slowed by the obstacle or to the enemy bypassing the obstacle. Key leaders are positioned where they can
  best assess the obstacle effect. If the enemy is rapidly breaching the obstacles, they may shift direct fires
  against the enemy breaching assets. If a large force bypasses, units may shift all fires against the unimpeded
  enemy to inflict maximum losses and then reposition friendly forces to subsequent positions.
  Fix Effect
  17-35. Fix is an obstacle effect that focuses fire planning and obstacle effort to slow an attacker’s movement
  within a specified area, normally an engagement area. The fix effect allows time to acquire, target, and
  destroy the enemy with direct and indirect fires throughout the depth of an engagement area or avenue of
  approach. The fix effect helps fires to defeat the enemy in detail or to gain the necessary time for forces to
  reposition while inflicting maximum casualties. To accomplish the fix effect, the obstacles and fires must—
  * Cause the enemy to deploy into attack formation early.
  * Cause the enemy to advance slowly into the engagement area.
  * Make the enemy fight in multiple directions within the engagement area.
  17-36. Units specify the amount of time or effect that the combined effect of fires and obstacles must
  achieve. The fix effect may generate the time necessary for the defending force to break contact and disengage
  as the attacking force maneuvers into the area. To achieve the fix effect, units array obstacles in depth to
  cause the attacking formation to react and breach repeatedly. The obstacles must influence the entire width
  of the avenue of approach but not make the terrain impenetrable. The individual obstacles must look as if
  they could be easily bypassed or reduced. Units combine obstacles that are clearly visible with others that are
  unseen (such as obstacles on the reverse slope help to confuse the attacking force once it encounters the
  obstacles).
  17-37. Units plan artillery- and aviation-delivered fires forward of the obstacles to suppress or neutralize
  the enemy. They synchronize indirect fires with long-range direct fires that cause the enemy to deploy out of
  a march or a prebattle formation. If the enemy is in an attack formation, this allows obstacles and fires to
  attack the full frontage of the enemy.
  17-38. Initially, units’ orient fires on the enemy force as a whole; however, destroying enemy breaching
  assets becomes increasingly important as the enemy continues to advance into the engagement area. To
  maximize obstacle effect and inflict maximum losses on the enemy, the fire plan requires an increase in the
  intensity of fires as the enemy advances. Units plan successive TRPs, integrated with obstacles closer to the
  BPs, which trigger engagement by additional weapons. They vary the intensity of fires through fire control
  to allow the enemy to continue a slowed advance. When the enemy fully commits, friendly forces complete
  its destruction.