The 5th RM Battalion was originally raised for a brief period at the end of World War I (September 1918-February 1919), and was again raised on 2 April 1940 following mass mobilisation and the influx of "hostilities only" (HO) marines. The battalion was raised at Cowshot Camp in Brookwood (now part of the Pirbright Camp complex), being incorporated into 101 RM Bde, along with the 1st RM Battalion. Between August and October 1940 the battalion took part in operations in Dakar. On return until August 1943 the battalion conducted extensive training in Wales, Scotland, the Isle of Wight and Burley, where the battalion reformed as 45 RM Commando on 1 August 1943. It was commanded between March 1940 and February 1942 by Arnold Reading.