When WWII broke out after Pearl Harbor, Troyce enlisted in the Army Air Force. His initial training was in Bangor, Maine. He served as a military policeman and was part of the Allies second wave on the Normandy coast on D-Day on the Omaha Beach. He was also in the Battle of the Bulge in the Argonne Forest and other military operations and was wounded in action. He received a number of awards and medals for his military service.