Cooke commissioned as a probationary second lieutenant on the General List, assigned to the
Royal Flying Corps on 24 May 1917, and received the Royal Aero Club Aviator's Certificate No. 4825 at the Military School at
Ruislip on 16 June after soloing in a
Maurice Farman biplane. Assigned to
No. 20 Squadron, Cooke's string of victories began on 22 January 1918 and extended until 19 May. His observers manning the guns in the rear seat of his
Bristol F.2 Fighter included fellow aces
Henry Crowe,
James Scaramanga and
Ernest Hardcastle. His final tally was five enemy fighter planes destroyed and eight driven down out of control, with nine enemy planes falling to his pilot's gun. as well as the award of the
Military Cross in July. He was transferred to the unemployed list on 26 July 1919. ==Honours and awards==