Officer Cadet John Arthur Groom was commissioned 7 November 1942. Served with No.4 Commando. Lieutenant Groom was awarded the Military Cross whilst attached to the Combined Operations Experimental Establishment (C.O.X.E.) for covert reconnaissance of beach mines and obstacles on the Normandy coastline during Operation Tarbrush on 16-17 May 1944, prior to the D-Day landings. 
Recommendation 
Lieutenant John Arthur Groom, C.O.X.E., Royal Engineers.
This officer was a member of a military force which landed in the vicinity of Bray-Dunes, N.E. coast of France, on the night of 16/17 May 1944, to carry out a detailed reconnaissance of beach mines and obstacles, the nature and potentialities of which were not known. Despite the presence of enemy patrols on the beach, Lt Groom, together with his NCO, swept a path with his mine detector up the beach towards the obstacles.
On arrival at these obstacles he proceeded to make, with the greatest courage and coolness, a careful and detailed examination of an object thought to be a new type of mine, and which might have been detonated by a device unknown to him and against which he could take no precautions. He followed this by a second examination, for comparison, of a similar object close by, and he took note and measurements of other obstacles in the vicinity. He then led his party back to the dinghy, in which they embarked and withdrew undetected.
Lt Groom was the first man of the force to approach and reconnoitre that object which was given the highest priority of the tasks allotted to the force, and in making a successful examination and in bringing this vital information back without leaving any trace of its having been obtained, he showed the greatest courage, efficiency, and coolness in face of the enemy.