Captain Sheehan was the pilot of a F-84E Thunderjet fighter with the 154th Fighter Bomber Squadron, 136th Fighter Bomber Wing. On 23 January 1952, while on a combat mission, his aircraft received a direct hit by anti-aircraft fire, his engine quit and he successfully crash landed near Oejang-do, Korea. He was taken Prisoner of War and declared dead on 31 March 1954. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

Sheehan was awarded the Air Medal with 2 Oak Leaf Clusters, the Purple Heart, the Prisoner of War Medal, 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.