Hepburn enlisted in the
Artists Rifles on 4 August 1916 and served in the trenches of France in the same year. He joined the Royal Flying Corps at Denham on 6 September 1916, flying the
Airco DH.5 in
24 Squadron of the RFC. He was slightly wounded in action in October 1917 and continued flying. In November he was posted to
40 Squadron of the RFC, but was injured in a crash and was sent to England to recuperate. In April 1918, Hepburn returned to duty flying a
Bristol F.2 Fighter, commanding the "A" Flight of
88 Squadron of the RAF. 88 Squadron later joined 80 Wing RAF where Hepburn flew side by side with the two
Australian Flying Corps scout squadrons. Allan Hepburn features in two stories in
Rothesay Stuart Wortley's book,
Letters of a Flying Officer (paperback from Alan Sutton, 1982). One of Hepburn's opinions reported in the book regards the use of radio, or wireless telephone, in the plane. "His chief objection to it is that one cannot stunt a machine with 150 feet of aerial trailing underneath the fuselage; and that one might very well find oneself involved in a scrap before one has the time to wind it up, with a possible result that the wire might get entangled in the propeller and so wreck the machine in mid-air." ==List of aerial victories==