A keen rower, Allen King was Captain of Boats in his final year at the school. On leaving PAC he commenced medicine at Adelaide University, later transferring to engineering and receiving his degree in 1939. In his spare time he was an active member of the Sporting Car Club of South Australia, driving an MG.
Having enlisted in the Royal Australian Naval Volunteer Reserve, King sailed from Australia and in Alexandria joined the cruiser HMAS Sydney in which he returned to Australia. HMAS Sydney was then deployed on patrol work in the Indian Ocean, where on 19 November 1941 it encountered the German raider Kormoran, which it engaged and sank. The Sydney was also lost and there were no survivors from her crew of 645 men.