Captain Horn was the pilot of a F-51D Mustang night fighter with the 39th Fighter-Interceptor Squadron, 18th Fighter Bomber Group. On 14 August 1951, while on a combat mission, his aircraft received a direct hit by anti-aircraft fire and crashed into the Taedong-ni River. He was listed as Missing in Action and was presumed dead on 31 December 1953. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

Horn was awarded the Air Medal, 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.