text: Chapter 6
  they can disrupt the advance of the main body. When the advance guard encounters large enemy forces or
  heavily defended areas, it takes prompt and aggressive action to develop the situation and, within its
  capability, defeat the enemy. The commander of the advance guard force reports the location, strength,
  disposition,and composition of the enemy and tries to find the enemy’s flanks,gaps,or other weaknesses in
  the enemy’s position.
  Covering Force
  6-135. A covering force’s mission is to protect the main body, provide early warning, reaction time, and
  maneuver space before committing the main body. The covering force is task organized to accomplish tasks
  independent of the main body. The covering force commander reports directly to the establishing commander
  (division or corps). The BCT normally does not have the organic resources or capabilities to establish a
  covering force. A covering force,if established,moves well ahead of the BCT’s advance guard and usually
  beyond the main body’s fire support range. (See FM 3-90-1 for additional information on the covering force.)
  Note. In Army doctrine, a covering force is a self-contained force capable of operating
  independently of the main body,unlike a screening or guard force, to conduct the cover task. A
  covering force performs all the tasks of screening and guard forces. (See paragraph 5-85 for
  information specific to a division covering force.)
  Flank and Rear Security
  6-136. The BCT establishes flank and rear security elements when their flanks or security area are
  unprotected. The BCT may use Cavalry organizations for flank security,or main body forces may provide
  flank (see figure 6-15) and rear security forces.