text: Chapter 4
  mobile reserve. Therefore, the mobile defense trades space and time for achieving a decisive advantage
  against the enemy. The defeat mechanism is a large, mobile reserve that must have combat power and
  mobility that are equal to or greater than the targeted force.
  The division engineer must understand the implications of a force-oriented defense on engineer
  functions and operations. Engineer support to the mobile defense concentrates on using obstacles to attack
  enemy maneuver and on preserving the mobility of the friendly force. Obstacle planning is more closely
  linked to the enemy’s most probable maneuver COA than to terrain. It must support attacking the enemy’s
  maneuver in a way that supports destruction by counterattack. Consequently, obstacle planning is more
  restrictive than permissive and reduces the flexibility of the brigades. This masses the brigade obstacle effort
  at critical areas and preserves the mobility of the counterattack force in the main battle area.
  Survivability effort is also tailored to a force-oriented defense that trades space and time for creating
  an enemy weakness to exploit by counterattack. To create the conditions for counterattack, brigades must
  fight the depth of their sectors from multiple primary and subsequent battle positions. Fortification efforts
  support fighting quick engagements from multiple positions by providing primary and alternate hull defilade
  fighting positions in primary and subsequent battle positions. The nature of the fight reduces the overall need
  for protective obstacles throughout the defense. Protective obstacle effort is concentrated in final subsequent
  positions, where the penetration must be blunted to allow counterattack.
  The defeat mechanism of the mobile defense is the counterattack by a large, mobile reserve with
  combat power and mobility that are superior to the targeted enemy force. The division engineer supports the
  mobility of the mobile reserve in two ways. First, obstacle control measures are used to ensure that brigade
  obstacle efforts do not limit the mobile reserve’s freedom to maneuver. Second, the division engineer ensures
  that the mobile reserve has the necessary dedicated engineer support to maintain its mobility during the
  counterattack. It must be able to counter the enemy’s offensive use of obstacles or reduce friendly obstacles
  as required by changes in the situation. Above all, the counterattack cannot be stalled by a lack of mobility.
  The division engineer must weigh the trade-offs between dedicating engineer forces to the counterattack and
  meeting the obstacle and survivability requirements of the main battle area.
  Area Defense
  The focus of the area defense is on the retention of terrain. The area defense is organized to absorb the
  enemy into an interlocked series of positions from which the enemy can be destroyed. In this pattern, the
  defeat mechanism is the interlocking nature of defensive positions and the small mobile reserves within
  subordinate defenses to defeat local penetrations. The area defense does not promise outright destruction of
  the attacker and may require other simultaneous or subsequent operations to achieve a decisive defeat of the
  enemy.
  The division engineer must understand the implication of the area defense on mobility and survivability
  requirements and engineer operations. Likewise, the scheme of engineer operations orients on the retention
  of terrain and on enabling the division to concentrate fires from fixed positions. The location of key and
  decisive terrain plays a major role in organizing the area defense and becomes the focus of obstacle and
  survivability efforts. Division obstacle planning uses obstacle control measures to give maximum flexibility
  to the brigades while still focusing tactical obstacle effort on the retention of terrain.
  Survivability effort must enable brigades to concentrate fire power from fixed positions. The division
  engineer must be sensitive to the increased hardening needs of the brigades in a division area defense. To
  fight from more fixed positions, the brigades may require primary, alternate, and supplementary turret-
  defilade positions. This is particularly true of brigades defending decisive terrain. The increased requirement
  for survivability also entails heavier employment of protective obstacles to break the attacker’s assault.
  Integrating defensive positions and small, decentralized, mobile reserves is a key component to
  enabling a complete defeat mechanism. The division engineer must ensure that the tactical obstacle effort of
  adjacent brigades is coordinated and mutually supporting and achieves an interlocking defense. Additionally,
  the division engineer must ensure that the engineer task organization provides the brigades dedicated mobility
  support of their respective mobile reserves.