ADP 3-90, page 78

Chapter 4 4-18 ADP 3-90 31 July 2019 BREAKOUT 4-111. A breakout is an operation conducted by an encircled force to regain freedom of movement or contact with friendly units. A breakout differs from other attacks only in that a simultaneous defense in other areas of the perimeter must be maintained. An encircled force normally attempts to conduct a breakout when—  Opportunity exists to attack.  An encircled force does not have sufficient relative combat power to defend itself against enemy forces attempting the encirclement.  An encircled force does not have adequate terrain available to conduct its defense.  An encircled force cannot sustain itself long enough to be relieved by forces outside the encirclement. EXFILTRATION 4-112. If the success of a breakout attack appears questionable, or if it fails and a relief operation is not planned, one way to preserve a portion of the force is through organized exfiltration. (See FM 3-90-1 for a detailed description of exfiltration.) ATTACKING DEEPER INTO ENEMY TERRITORY 4-113. A COA that enemy forces do not expect from an encircled force is to attack deeper to seize key terrain. It involves great risk, but it may offer the only feasible COA under some circumstances. Attacking may allow an encircled unit to move to a location where it can be extracted by other ground, naval, or air forces. Attacking deeper is only feasible if a unit can sustain itself while isolated, although sustainment can come from aerial resupply and enemy supply stocks. 4-114. When an enemy is attacking, an encircled friendly force that attacks deeper into the enemy rear area may disrupt the enemy’s offense and provide an opportunity for linkup from another direction. If an enemy is defending and the attacking force finds itself isolated, it may continue the attack toward its assigned objective or a new objective located on more favorable defensive terrain. LINKUP 4-115. A linkup is a meeting of friendly ground forces, which occurs in a variety of circumstances. It happens when an advancing force reaches an objective previously seized by an airborne or air assault forces. A linkup can also occur when an encircled element breaks out to rejoin friendly forces or a force comes to the relief of an encircled force. It also occurs when converging maneuver forces meet by moving toward each other, or when one force is stationary. Whenever possible, joining forces exchange as much information as possible before starting a linkup operation. The headquarters ordering the linkup establishes—  The common operational picture.  The command and support relationship and responsibilities of each force before, during, and after linkup.  FSCMs and direct fire control measures.  The linkup method.  Recognition signals and communication procedures.  Subsequent operations. TRANSITION 4-116. Defending commanders assess the success of their defense and determine if they can transition to the offense. If a defense is unsuccessful, defending commanders transition into retrograde operations. Transition from one type of operation to another requires mental as well as physical agility from the involved formations and an accurate understanding of the situation.