The mission of Marine Forces Reserve is to augment and reinforce active Marine forces in time of war, national emergency or contingency operations, provide personnel and operational tempo relief for the active forces in peacetime, and provide service to the community (for example, through Toys for Tots).
MARFORRES comprises two groups of Marines and Sailors. The first, known as the Selected Marine Corps Reserve (SMCR), are Marines who belong to reserve units and drill one weekend a month and two weeks a year. The second group is known as the Individual Ready Reserve (IRR). The IRR is composed of Marines who have finished their active duty or USMCR obligations, however their names remain on the books to be called up in case of a war or other emergency—the Individual Ready Reserve is administered by the Marine Corps Mobilization Command. IRR Marines participate in annual musters to check in with the Corps. Reserve Marines are equipped and trained to the same standards as active Marine forces.
The mission of the 4th Marine Division is to provide trained combat and combat support personnel and units to augment and reinforce the active component in time of war, national emergency, and at other times as national security requires; and have the capability to reconstitute the Division, if required.