Douglas argued for a more aggressive engagement with a "Big Wing" strategy, i.e. using massed fighters to defend the United Kingdom against enemy bombers.

43 Squadron, flying Sopwith 1½ Strutters on the Western Front, in April 1916 and, having been promoted to temporary major on 1 July 1916, he became then officer commanding No.

[19] After the war Douglas worked briefly for Handley Page and as a commercial pilot before rejoining the Royal Air Force in 1920 after a chance meeting with Hugh Trenchard.

[11] After being granted a permanent commission as a squadron leader on 25 March 1920,[20] Douglas attended the RAF Staff College and then served as a flight instructor four years.

[15] Promoted to wing commander on 1 January 1925,[21] he continued his work as an instructor before attending the Imperial Defence College in 1927.

Douglas argued for a more aggressive engagement with a 'Big Wing' strategy i.e. using massed fighters to defend the United Kingdom against enemy bombers.

[29] He was advanced to Knight Commander of the Order of the Bath on 1 July 1941[30] and promoted to the substantive rank of air marshal on 14 April 1942.

He was therefore one of the main orchestrators of the only partially successful Circus offensive whereby large wings of fighters accompanied by bombers would take advantage of good weather to sweep over Northern France.

[34] In that capacity Douglas was an advocate of Operation Accolade, a planned British amphibious assault on Rhodes and the Dodecanese Islands in the Aegean Sea, and was disappointed when it was abandoned.

[37] Promoted to Marshal of the Royal Air Force on 1 January 1946,[38] Douglas became the second commander of the British Zone of Occupation in Germany in May 1946.

[15] He was raised to the peerage as Baron Douglas of Kirtleside, of Dornock in the County of Dumfries on 17 February 1948, sitting as a member of the Labour Party.