Shortly before the outbreak of World War II, Fiske was recalled to the New York offices of Dillon, Reed & Co, but on 30 August 1939 he returned to England aboard the "Aquitania" accompanying a bank colleague who was also a member of No. 601 (County of London) Auxiliary Air Force Squadron. Fiske was one of seven US aircrew personnel who fought in the Battle of Britain, although due to the neutrality of the United States, Fiske pretended to be a Canadian. He joined the Royal Air Force Volunteer Reserve and was promoted to the rank of Pilot Officer on 23 March 1940.