text: Movement and Forms of Maneuver
  2-57. Divisions and corps may initiate an attack by simultaneously launching two or more convergent
  penetrations against weak locations on the enemy front. Often this method of attack helps isolate an extremely
  strong enemy defense. Units assign supporting efforts to contain any enemy positions that may influence the
  penetration.
  ENVELOPMENT
  2-58. Envelopment is a form of maneuver in which an attacking force avoids an enemy’s principal
  defense by attacking along an assailable flank. An envelopment avoids the enemy force’s strength—the
  enemy’s front—where the effects of enemy fires and obstacles are generally the greatest and attacks the
  enemy to the flank or rear. Envelopments force the enemy to fight in two or more directions simultaneously
  to meet the converging efforts of an attack. Envelopments focus either on seizing terrain, destroying enemy
  forces, or interdicting enemy withdrawal routes. Units prefer to conduct an envelopment instead of a
  penetration or a frontal attack because generally the flanks of the defending forces are weaker and provide
  the attacking forces the most opportunities to destroy the enemy force. The main effort focuses on attacking
  an assailable flank. If no assailable flank is available, the attacking force creates one through the conduct of
  a penetration. The three variations of the envelopment are—
  * Single envelopment.
  * Double envelopment.
  * Vertical envelopment.
  2-59. A single envelopment is a variation of envelopment where a force attacks along one flank of an
  enemy force. A single envelopment is generally easier to control and does not require a significant number
  of forces. See figure 2-16 on page 2-20 for an illustration of a single envelopment.
  2-60. A double envelopment is a variation of envelopment where forces simultaneously attack along
  both flanks of an enemy force. A force seeking to execute a double envelopment must also have a substantial
  mobility advantage over defending forces. A unit performs a double envelopment by conducting a frontal
  attack to fix enemy forces in place while enveloping both of the enemy force’s flanks. A double envelopment
  generally requires more forces than a single envelopment and are more difficult to control.
  2-61. A vertical envelopment is a variation of envelopment where air-dropped or airlanded troops
  attack an enemy forces’ rear, flank, or both. A force seeking to execute a vertical envelopment requires
  the necessary vertical lift capability and indirect fire assets to suppress enemy air defense capability. Because
  of the forces required, normally only divisions and larger organizations can conduct double and vertical
  envelopments, since these organizations have the resources and the capability to control these envelopments.
  A vertical envelopment, by either airborne assault or air assault, allows the commander to—
  * Overcome distances quickly, overfly barriers, and bypass enemy defenses.
  * Extend the area over which the commander can exert influence.
  * Leaves the enemy defenses more vulnerable to attack from the main body.
  * Disperse reserve forces widely for survivability reasons while maintaining their capability for
  effective and rapid response.
  * Exploit combat power by increasing tactical mobility.
  * Seize key terrain to deny the enemy’s use.