A graduate of the University of Maryland, Lieutenant Colonel Clapp was commissioned a second lieutenant and received the wings of a Naval Aviator upon completion of flight training at Pensacola, Florida, in July 1943. During World War II, he participated in the Iwo Jima and Okinawa campaigns and in the first carrier-based raid on Tokyo. He served in Korea from 1952-1953, where he flew combat support missions as a helicopter pilot and as an attack aircraft pilot.