Landing Craft Obstruction Clearance Unit - LCOCU.
In the Normandy landings on 6 June 1944, Nos 7 and 8 were with Force S, Nos 9 and 10 with Force G, and 11 and 12 with Force J. They were all intended to clear paths through beach obstacles, but owing to the conditions of the tide and dangers from incoming craft the men were unable to use their shallow water diving gear, but nevertheless cleared obstacles.
The Unit comprised of 120 men from the RN and RM including the RM Engineer Commando. Pathé News produced a post-war film about the Naval Frogmen in the LCOCU.
Sources
The Royal Marines 1919-2000, J.D.Ladd.
Links below.