Coombes was awarded the Distinguished Flying Cross (DFC) on 3 August,[8] then returned to England to spend the rest of the war serving as an instructor at No.
[5] Coombes left the RAF on 17 April 1919,[9] and spent the rest of the summer barnstorming around the north of England in surplus B.E.2's with Charles Kingsford Smith[2] before returning to City and Guilds College, to finally receive his Engineering degree in mid-1920.
[3] After four years working for C. A. Parsons & Co. in Newcastle upon Tyne, Coombes joined the Royal Aircraft Establishment as a Scientific Officer in the Aerodynamics Department.
A year later, in 1925, he moved to the Marine Aircraft Experimental Establishment at Felixstowe,[10] where he also acted as a technical advisor to the RAF's High Speed Flight, competing for the 1927 Schneider Trophy.
[10] In 1938 Coombes emigrated to Melbourne, Australia, after being appointed the first Chief Superintendent of the Aeronautical Research Laboratories (ARL).
[2][10] In 1960, while serving as an advisor for the United Nations, Coombes helped India establish its first Aeronautical Research Laboratory.