Formed on the 14th February 1942 as The RM Commando, it was briefly known as "A" RM Commando before being designated 40 RM Commando. Served in Dieppe, St Benere, Termoli, Anzio. Comacchio during WW2.
40 RM Commando, and the slightly later formed 41RM Commando, would be the only RM Commando units to consist entirely of volunteers. All Army Commandos were volunteers.
40 RM Commando was disbanded early in October 1945, before reforming as 40 Commando RM when 44 RM Cdo was disbanded and redesignated.