Unless he was in the Navy or Army Armed Guards then he was not considered In the "military" at the time. It was on in the 1980s was a bill passed granting them "Veteran" status. At least in the U.S. Military. The Name "Marines" in Merchant Marines refers to Mariners, men of the sea.
http://www.usmm.orgAlso look at ship passenger and crew lists if he worked after the war or before FamilySearch.org and Ancetry has some lists online. A local Family History Center may have microfilms or bound books of them. Look at the online catalog.