John A. Kapinos entered the military service in Massachusetts. He served in the U.S. Army during World War II as a Private in the 531st Engineer Shore Regiment. He was killed during the Exercise Tiger--one of the large-scale rehearsals for the D-Day invasion of Normandy. This took place in April 1944 in Slapton Sands, Devon in the UK. An Allied naval convoy involved in the exercise was attacked by German submarines, and coordination and communication problems resulted in friendly fire deaths. At least 749 American servicemen were killed. Because of the impending invasion of Normandy, the incident was highly classified and the full story did not come out until years later after the war. He was declared "Missing in Action" on April 28, 1944 and is commemorated on Tablets of the Missing, Cambridge American Cemetery, Cambridge, United Kingdom.