Coke joined the Royal Air Force Volunteer Reserve (RAFVR) in June 1939, the summer before war broke out, and attended No. 5 Operational Training Unit in April 1940. He was promoted to the rank of acting pilot officer on 3 September 1940. By August 1940 he flew a Hawker Hurricane with No. 257 Squadron RAF during the Battle of Britain as a pilot officer. On 12 August 1940, his Hurricane (P3776) was badly shot up over the English Channel off Portsmouth. His finger was amputated and the aircraft was repaired. Posted to 46 Squadron in December 1940, Coke was then promoted to flying officer.