7-44. Commanders may also commit the reserve to sustain the momentum of the attack of a committed unit. There are three basic options for the use of the reserve in this case. First, the reserve continues the attack as a separate force under the control of the corps or division headquarters, and it is given responsibility for the remainder of the committed unit’s AO. The second option is to place the reserve in a command relationship— attached, OPCON, or TACON—to the committed unit. This reinforces the committed division or BCT whose commander is probably most knowledgeable of local conditions without needing to change control measures. The third option is for the reserve to assume control of the AO from the committed unit by means of a passage of lines, a relief in place, or a follow on and assume tactical mission task. This allows the rapid introduction of fresh forces. It also allows the higher commander to reconstitute a reserve from the formerly committed unit after that unit has had enough time to resupply and reorganize itself.