History of 503 Squadron:
No.503 Squadron was formed at Waddington on 5 October 1926 as a Special Reserve unit. As a bomber squadron, it was initially equipped with Fawns, but received Hyderabad night bombers in 1929 and in 1933 its improved version, the Hinaidi. In October 1935, No.503 became a day bomber squadron and received Wallaces, these being replaced by Harts in June 1936. After being transferred to the Auxiliary Air Force on 1 May 1936, Hinds began to arrive in July 1938. The squadron disbanded on 1 November 1938, its aircraft and personnel going to No.616 (South Yorkshire) Squadron, which formed on the same day at Doncaster.