text: Security Operations
  * Eliminate enemy forces bypassed by the security force.
  * Coordinate and conduct a forward passage of lines through the security force and fix enemy forces
  in the enemy’s main defensive positions to allow the friendly main body to maneuver.
  13-84. The movement of multiple security forces and the handover of a detected enemy force from the
  higher echelon security force to the lower echelon security force are controlled using checkpoints, contact
  points, PLs, handover lines, and disengagement criteria, in addition to other graphic control measures. At a
  minimum, the higher echelon security force has a rear boundary that is also the forward boundary of the
  advance guard.
  13-85. The advance guard engages in offensive operations when necessary to accomplish the mission. After
  the guard makes enemy contact, the commander determines whether the guard mission requires an attack, a
  defense, or a delay based on the mission variables. For example, if the guard force has sufficient combat
  power to defeat an enemy force, it conducts a hasty attack. The guard force avoids assaulting strong enemy
  positions from the front. If the enemy forces attempt to withdraw, the advance guard continues the attack
  with the intent to destroy the enemy force. If the advance guard encounters an enemy force that it cannot stop
  from interfering with the movement of the main body, the security force reports its presence to the main
  body. It then establishes a defense, continues conducting reconnaissance, and prepares to pass elements of
  the main body forward while facilitating the deployment of the main body.
  13-86. Guard force units can delay rearward one or more positions to avoid decisive engagement if the
  depth of the security area permits, and they do not have enough combat power to defeat an approaching
  enemy force. This reduces the enemy force’s combat power. Guard forces accept decisive engagement to
  prevent enemy ground forces from employing their direct-fire systems to engage the main body unless their
  higher echelon commanders relieve them of their mission.
  Flank Guard
  13-87. A flank guard protects an exposed flank of the main body. A flank guard is similar to a flank screen
  except that the unit plans defensive positions in addition to observation posts.
  13-88. Main body units assign an area to each flank guard that is sufficiently deep to provide early warning
  and reaction time. However, each flank guard remains within supporting range of the main body’s indirect
  fire systems. Flank guard units consider the front and rear of the flank of the main body, the axis taken by
  the main body, the enemy’s capabilities, and the available avenues of approach when determining the exact
  positions their forces initially occupy.
  13-89. Each flank guard moves to its initial positions using one of the movement techniques. On reaching
  its initial position, the flank guard establishes defensive positions in assigned BPs or in its assigned area and
  establishes a screening element forward of these positions. In situations where knowledge about the enemy
  force is vague, the flank guard maintains a larger reserve than in situations where the enemy force’s actions
  are more predictable. Figure 13-10 on page 13-22 depicts an example stationary flank guard.