text: Support to Large-Scale Ground Combat
  * Retrograde. Mobility and countermobility are normally the focus of engineer support to a
  retrograde. The priority of effort depends on whether the unit is in contact with the enemy. The
  underlying purpose of engineer support to the retrograde is twofold as follows:
   The mobility of the force must be maintained, regardless of the type of retrograde being
  conducted. Mobility focuses on maintaining the ability of the force in contact to disengage
  while preserving the main body freedom of maneuver.
   The force must be protected because they are particularly vulnerable to enemy actions during
  retrograde operations. Consequently, a retrograde is normally conducted under limited-
  visibility conditions. Engineers support units left in contact and extend the time available to
  the commander by reducing enemy mobility through obstacles, fires, and terrain optimization.
  The primary defensive tasks use mobile and static elements. In mobile defense, static positions help
  control the depth and breadth of enemy penetration and retain ground from which to launch counterattacks.
  In area defense, commanders closely integrate mobile patrols, security forces, sensors, and reserves to cover
  gaps among defensive positions. In retrograde operations, some units conduct area or mobile defenses and
  security operations to protect other units that are executing carefully controlled maneuver or rearward
  movement. Static elements fix, disrupt, turn, or block attackers and gain time for other forces to pull back.
  Mobile elements constantly maneuver to confuse the enemy and prevent enemy exploitation.
  Defensive Operations Planning
  Planning for the defense is inextricably linked to offensive operations and, for planning purposes,
  planners conducting the military decisionmaking process (MDMP) should consider the transition from the
  offense and the follow-on offensive operations. Engineers work directly with tactical maneuver units during
  the seven steps of enagement area (EA) development. EA development (explained in ATP 3-90.8) consists
  of the following steps:
  * Step 1. Identify likely enemy avenues of approach (AAs).
  * Step 2. Determine likely enemy scheme of movement and maneuver.
  * Step 3. Determine where to kill the enemy.
  * Step 4.* Plan and integrate obstacles.
  * Step 5.* Emplace weapon systems, to include the preparation of fighting positions.
  * Step 6.* Plan and integrate observation and indirect fires.
  * Step 7. Conduct an EA rehearsal.
  Note. Although the steps are listed sequentially, the steps marked by an asterisk (*) should be
  conducted simultaneously.
  During the preparation of the defense, engineers use geospatial products to assist with all aspects of
  EA development (AAs, mobility corridors, obstacle emplacements to enable overwatch, an array of friendly
  forces to depict the most advantageous lines of sight, indirect fire target reference points). Engineers then
  work with intelligence staffs to describe the threat and to predict where the enemy is likely to attack friendly
  forces. Engineers also work in conjunction with intelligence staffs to determine sensor capabilities that would
  be leveraged to prevent the enemy from maneuvering freely into the defended area. Defensive operations
  planning includes security and survivability considerations. The consideration of counterattack planning or
  support for the mobile strike force is the same as the typical mobility planning for the offense. The engineer
  staff officer works with the other staff members to ensure that the counterattack force can mass its effects on
  the enemy for decisive operations. This form of defense helps to define the amount and focus of engineer
  effort required. An area defense typically requires a more robust engineer effort due to an increased
  survivability requirement. A mobile defense typically requires less effort because it has greater flexibility
  and takes advantage of the terrain in depth.
  Mobile Defense
  The focus of mobile defense is the destruction of the enemy attacker. The mobile defense is organized
  to permit the enemy to advance into a position that exposes them to counterattack and envelopment by a