Gunn enlisted in the
Royal Air Force on 22 February 1940 and commenced active service on 22 June 1940 as an aircrew candidate (
aircraftsman 2nd class). He began his flying training at
RAF Ansty near Coventry, and later at
Blackpool. On 18 January 1941 he received his
pilot's brevet and promotion to
sergeant. He was commissioned as a
Pilot Officer on 25 January 1941. Gunn joined
No. 48 Squadron RAF of
RAF Coastal Command flying
Avro Anson aircraft on photo reconnaissance missions. A reliable record flying with the squadron led to Gunn being posted to
RAF Benson to fly stripped-down high-altitude conversion
Supermarine Spitfires with
1 Photographic Reconnaissance Unit in September 1941. In January 1942 he was posted to
RAF Wick in the north of Scotland. Wick was a noted photo reconnaissance aerodrome; in May 1941, a Spitfire from Wick found and photographed in a Norwegian fjord.
Bismarck was later sunk by the Royal Navy, but remained a threat in Norway. Gunn was promoted to
Flying Officer on 25 January 1942, and flew many long-range missions over German naval units on the Norwegian coast and in the North Atlantic, often in terrible weather. On one occasion he crashed in the North Atlantic after his aircraft ran out of fuel. ==Prisoner of war==