No. 19 Squadron was stationed at RAF Duxford after the outbreak of the Second World War in September 1939, and was part of No. 12 Group, RAF Fighter Command. Douglas Bader was posted to the squadron in February 1940. In May and June 1940, the squadron helped provide air cover over the Dunkirk beaches. In June 1940, No. 19 Squadron began the receive Spitfire Mk.Ibs, which were armed with the Hispano cannon, however due to reliability issues the unit soon reverted to the Spitfire Mk.Ia. No. 19 Squadron formed part of the Duxford Wing, No. 12 Group's 'Big Wing' formation during the Battle of Britain.