 During World War II, O'Connor served in the European Theater of Operations as a pilot in Italy with the 459th Bombardment Group, Fifteenth Air Force.He returned to the United States in September 1944 and attended the Command and General Staff School at Fort Leavenworth, Kan., from October 1944 to January 1945.He then served at Muroc Army Air Base (now Edwards Air Force Base), Calif., until April 1946 when he entered the Air Force Institute of Technology at Wright-Patterson Air Force Base.