7-38. The reserve is that portion of a body of troops which is withheld from action at the beginning of an engagement, in order to be available for a decisive movement (ADRP 3-90). It is a commander’s principal means of influencing the action decisively once an operation is under way. A reserve is not committed to a particular course of action. It does not have a planned, subsequent mission. Its commitment solely depends on the flow of the battle. The commander establishes its planning priorities for likely contingencies. A reserve reinforces or maintains the attack’s momentum by—