2-73. While joint doctrine has three definitions for reserve, the following Army definition applies to Army tactical operations. A reserve is that portion of a body of troops that is withheld from action at the beginning of an engagement to be available for a decisive movement. A reserve is an uncommitted force and thus does not normally have a full suite of combat multipliers available to it until it is committed. It is normally the echelon’s main effort once it is committed. Commanders constitute a reserve and base the size of the reserve on the level of uncertainty in the current tactical situation. Commanders consider survivability and the most likely mission when positioning their reserve. While commanders can assign their reserve a wide variety of tasks to perform on commitment, a reserve remains prepared to accomplish other missions. The primary tasks for a reserve are to—