text: Support to Large-Scale Ground Combat
  Retrograde
  Retrograde operations involve organized movement away from the enemy (including delays,
  withdrawals, and retirements). Retrograde operations—
  * Gain time.
  * Preserve forces.
  * Place the enemy in unfavorable positions.
  * Avoid combat operations in undesirable conditions.
  Engagement Area Development
  Terrain shaping affects the enemy’s ability to move and maneuver. Terrain shaping enables friendly
  forces to engage the enemy at a desired place and time. The employment of obstacles must be linked with
  the maneuver commander’s intent on how and where to deploy the bulk of the unit’s combat power and
  conduct decisive operations to defeat an attacking enemy. To mass resources, EAs are critical maneuver
  corridors that are important to both friendly and enemy forces. Every obstacle, barrier, and minefield is
  created to support the maneuver plan and to be evaluated from both an offensive and a defensive posture.
  Successful EAs allow for obstacles to be linked to restrictive terrain or natural obstacles. These constructed
  obstacles vary by type and with time and supply constraints. Resources and barrier types include networked
  mines, scatterable mines, demolition obstacles (such as road craters), constructed obstacles, and field
  expedient obstacles.
  Obstacle siting is a support rehearsal that is focused on the integration of obstacles and fires. It is
  considered a support rehearsal because it supports the EA rehearsal that occurs as the last step in the EA
  development process. Engineers must walk the terrain in conjunction with the supported maneuver unit to
  ensure that fires cover the EA. See ATP 3-90.8 for more information on the seven steps of EA development.
  ENGINEER SUPPORT TO THE THEATER ARMY
  The goal of the defense is to defeat the enemy’s attack and to quickly transition to the offense. To reach
  this goal, engineers provide synchronized engineer efforts to prioritized deep, close, and support areas. See
  ATP 3-90.8 and FM 3-90-1.
  Theater army engineer operations apply technical capabilities to create favorable conditions for any
  combination of operational elements. While the influence of distinct operational elements may be lessened
  for some technically focused engineering tasks, the overall engineer effort must remain integrated within a
  combined arms framework. The theater echelon engineer staff (either from the TEC or echelon engineer staff
  section) participate in the operations process to synchronize the orchestration and sustainment of primarily
  subordinate echelon engineer actions and the application of more technically focused engineer capabilities.
  Some generalities can be observed when considering the operational elements and strategic objectives.
  For large-scale ground combat, a significant portion of the tailored engineer force tends to have
  command relationships to maneuver commanders. The tailored engineer force is pushed using command
  relationships in the task organization to tactical echelons for close support of combat operations. This is true
  for some general engineering capabilities and for most combat engineering capabilities. Movement and
  maneuver requirements are not well defined at higher echelons and are more dynamic in combat operations.
  Tailored forces are pushed to subordinate echelons to address these requirements and add flexibility for those
  maneuver commanders to react to unforeseen challenges and opportunities.
  For defensive operations, operational echelon engineer planners are not typically able to generate
  adequate construction capabilities to support the subordinate requirements for movement and maneuver
  (countermobility) and protection (survivability). Operational requirements compete for these same
  capabilities. Planners recommend priorities for engineer capabilities and then work collaboratively with
  unified action partners and subordinate elements to mitigate shortfalls.
  Obstacle-emplacement authority is the authority that a commander has to emplace reinforcing
  obstacles. Theater commanders are normally delegated the emplacement authority, which is aligned with the
  theater rules of engagement. Theater commanders delegate that authority to corps commanders who delegate