414624 Sergeant William Alexander MacKay enlisted in the Royal Australian Air Force in Brisbane, Queensland on 13 October 1941. He trained as a wireless air gunner in December 1941, after completing training at Bombing and Gunnery School. He was promoted to Leading Aircraftman on December 1941, and in July 1942 promoted to Sergeant. Sergeant MacKay was posted in February 1943 to 41 Radio Direction Finding Wing attached to the 63rd Bomber Squadron, United States Army Air Force. He served as a Wireless Air Gunner/Radar Counter Measures Operator in Port Moresby, New Guinea.
On 30 June 1943 he was killed in action over New Guinea whilst assisting in the bombing operations of the 63rd Bomber Squadron, USAAF. The wreck and remains of the crew were found in 1947. Sergeant MacKay is buried at St Louis (Jefferson Barracks) National Cemetery.