He joined the Royal Air Force in August 1940 and trained as a pilot. His first posting was to 603 Squadron where he flew the Supermarine Spitfire on operations over France and convoy protection patrols. Later in 1941 Colquhoun was delivering a photographic reconnaissance Spitfire to Cairo but during a stop at Malta he was ordered to join 69 Squadron when the it was decided that their need for a PR Spitfire was more important. For nine months in 1941 and 1942 Colquhoun flew operational sorties in his unarmed and pale blue painted Spitfire over Italy. By the time more aircraft arrived in May 1942 aboard HMS Eagle Colquhoun had carried out 154 operational sorties. For his work with 69 Squadron Sergeant Colquhoun was awarded the Distinguished Flying Medal and commissioned as a Pilot Officer. Colquhoun returned to the United Kingdom where he trained to fly the photographic reconnaissance variant of de Havilland Mosquito at 2 OTU in Scotland. In 1943 he joined 682 Squadron based in Algeria and later moved to Italy. He stayed with the squadron until October 1944 and carried out 262 operational sorties. For his work with 682 Squadron he was awarded the DFC. After a short period as an instructor at 2 OTU he was posted to Vickers Supermarine as a production test pilot. He was part of a team that test flew Spitfires as they left the production lines.
Test pilot
In 1946 when he left the RAF he was invited to remain at Vickers as part of the test flying team. He soon showed an aptitude for testing new types and was soon involved in the testing of new naval fighters the jet-powered Attacker and Scimitar. In May 1950 Colquhoun was flying an Attacker to test the effectiveness of the air brakes. On the third of two dives the outer portion of the starboard wing folded up and the ailerons became locked. Colquhoun decided not to eject and managed to do a high-speed landing at Chilbolton, he used all but the last 100 yards of the runway and burst a tyre. He had saved the aircraft so the cause could be discovered and was awarded the George Medal for his efforts.
Hovercraft
Colquhoun was soon testing the new hovercraft being produced by Vickers and went on to become operations manager of Vickers' Hovercraft division. In 1962 Colquhoun piloted a Vickers VA-3 on the first public hovercraft service which was between Wallasey and Rhyl. In 1966 he joined Hoverlloyd as operational manager for the cross channel hovercraft service, he later becoming managing director. When Hoverlloyd was taken over by Seaspeed he then ran their jetfoil service to Dieppe.
Later life
Colquhoun became custodian of Chiddingstone Castle before he retired to live at Broadstairs in Kent. He died in 2001 leaving a wife and four daughters.
