text: Chapter 2
  Figure 2-16. Single envelopment
  Organization of Forces
  2-62. During a single or double envelopment units organize their forces to perform two primary tasks: fixing
  the enemy force and executing the envelopment. Units conducting an envelopment task organize forces into
  a fixing force, enveloping force, security force, and a reserve. The only organizational difference between a
  single envelopment and double envelopment is that a double envelopment consists of two enveloping forces.
  The fixing force normally conducts a frontal attack to fix enemy forces in their current positions to prevent
  their escape and reduce their capability to react against the enveloping force. The fixing force should use the
  minimal amount of combat power to fix the enemy while ensuring the majority of combat power is in the
  enveloping force. During a double envelopment, commanders typically designate the most likely to succeed
  of the two envelopment operations as the main effort for resources. The enveloping force maneuvers behind
  the enemy’s battle zone to defeat enemy forces in their positions, but from an unexpected direction. The
  security force prevents the enemy from discovering friendly dispositions, capabilities, and intentions, or
  hindering the envelopment.
  2-63. Units executing a vertical envelopment organize friendly forces into an air assault task force or an
  airborne task force. The air assault task force is a temporary group of integrated forces tailored to a specific
  mission under the command of a single headquarters. The air assault task force consists of an air assault force
  and the ground assault force. The ground assault force is task-organized with enough combat power to seize
  or fix the objective or enemy force. The airborne task force is organized by an assault echelon, follow-on
  echelon, and rear echelon. The assault echelon is task-organized with enough combat power to seize or fix
  the objective or enemy force. (See FM 3-99 for more information on airborne and air assault operations.)
  Control Measures
  2-64. At a minimum, commanders assign an area for each unit participating in an envelopment. They also
  designate phase lines, support by fire and attack by fire positions, contact points, and appropriate fire
  coordination measures, such as a RFL or boundary between converging forces, and any other control
  measures necessary to control the envelopment. Figure 2-17 is an example of control measures used when
  conducting an envelopment.