text: Chapter 11
  infiltrate or insert forces ahead of the withdrawing force, commanders may establish an advance guard to
  clear the route or assigned areas. They designate a flank guard or screen, as the situation requires.
  11-77. When a security zone exists between the two main opposing forces, the existing security force can
  transition on order to a rear guard or rear covering force. It then conducts delay operations until commanders
  order it to disengage and break contact with the enemy force. When the withdrawing force is in close contact
  with the enemy force, a security zone does not normally exist. Withdrawals under these conditions require
  that security forces adopt different techniques. For example, the detachment left in contact establishes a way
  to break contact sequentially with the enemy force.
  11-78. The main body of the withdrawing force consists of all elements remaining after the senior
  commander resources a security force and reserve. Commanders in a withdrawal generally find it difficult to
  resource a reserve, but they make every attempt to do so. When the complete formation withdraws under
  pressure, the reserve may take limited offensive action, such as spoiling attacks, to disorganize, disrupt, and
  delay the enemy force. It can counter penetrations between positions, reinforce threatened areas, protect
  withdrawal routes, and free encircled or heavily engaged forces.
  Withdrawal Control Measures
  11-79. Withdrawing forces protect themselves while simultaneously moving combat power away from
  enemy forces. This requires careful coordination among all forces. Throughout an operation, commanders
  strictly control rearward movement and maintain the ability to concentrate combat power at key times and
  places. Figure 11-5 illustrates that commanders use the same control measures in the withdrawal that they
  employ in the delay or the defense. Withdrawal control measures also include the routes used by each unit in
  the withdrawal and their movement times.
  Figure 11-5. Example control measures for a withdrawal using a detachment left in contact