First Lieutenant Gillespie was the pilot of a F-80C Shooting Star fighter interceptor with the 26th Fighter Interceptor Squadron, U.S. Air Force. On 12 May 1951, he was on temporary duty with the 16th Fighter-Interceptor Squadron, 51st Fighter-Interceptor Group. While on a combat mission against the marshalling yards at Sunan, his aircraft received a direct hit by anti-aircraft fire and crashed. He was listed as Missing in Action and was presumed dead on 31 January 1954. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

Gillespie was awarded the Air Medal with Oak Leaf Cluster, the Purple Heart, the Korean Service Medal, the United Nations Service Medal, the National Defense Service Medal, the Korean Presidential Unit Citation and the Republic of Korea War Service Medal.