The Royal Marines Reserve (RMR) is the volunteer reserve force used to augment the regular Royal Marines. The RMR consists of some 600 trained ranks distributed among the four units within the UK. About 10 percent of the force are working with the Regular Corps on long-term attachments in all of the Royal Marines regular units. All the volunteers within the RMR must pass through the same rigorous commando course as the regulars. The former may be civilians with no previous military experience or may be former regular Royal Marines.

Matthew Croucher, is a member of the Royal Marines Reserve and a recipient of the George Cross, the highest British and Commonwealth medal for gallantry not in the face of the enemy, for his extreme valour in risking his life to safeguard the lives of his comrades. The award was announced by the Ministry of Defence on 23 July 2008, and gazetted on 24 July 2008, with a lengthy citation.