Members included cooks, clerks, wireless telegraphists, and electricians. It was formed in 1916 during the First World War, and by the end of the war had 5,500 people, 500 of them officers.
It was revived during the Second World War, with an expanded list of allowable activities, including flying transport planes. At its peak in 1944 it had 75,000 people. During the war there were 100 deaths. It was eventually wound down again in the 1950s, and was finally integrated into the regular Royal Navy in 1993.