The Royal Marine Engineers were part the Royal Marine Division raised in 1940. They were originally designated 18 Battalion (Mobile) RM and received training in assault engineering and demolitions from the Royal Engineers with some men being trained as divers, by the Royal Navy. The Division never saw combat as a unit, being constantly depleted of personnel for other duties.
In 1943 the Royal Marine Division was disbanded and the engineers received commando training and a new name.
From 25 October 1943 the first War Establishment was: HQ; Holding Troop; and two fighting Troops (Source: RM Circ 1303/43G dated 26 November 1943). By June 1944 there were 180 all ranks, forming a small HQ with a Training Troop (the Holding Troop) and two fighting Troops. These were reorganised for the Normandy invasion with HQ and Training Troop in the UK, one Section with 1st SS Bde, one Section with 4 SS Bde, and six Landing Craft Obstruction Clearance Units.
Sections with Special Service/Commando Brigades
The Section with 1st Special Service Bde of 39 all ranks commanded by a lieutenant, landed in Normandy on 6 June 1944 at H+75 minutes to demolish bridges; but these were still in enemy hands and this Section prepared the defences of Brigade HQ; later they were employed in mine clearing and building strongpoints. They also improvised bridges and fords before returning to the UK on 9 September 1944. The Section which joined 4 Special Service Bde arrived in France at the end of June 1944 and served in mine clearing, demolition and other work of assault engineers. In November 1943 a third Section served in the Far East. This Section had joined 3 Commando Brigade in November 1943 and was increased to a Troop in the late summer of 1944. It built the roads at Myebon (from 12 January 1945) and at Kangaw (from 19 January), under appalling conditions on both occasions.
Landing Craft Obstruction Clearance Units
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. [Source: The Royal Marines 1919-2000 by J.D. Ladd.] [1]