It was formed as a fighter squadron at RAF Catterick in Yorkshire on 21 July 1941. The squadron was manned by exiled Norwegians, except for the ground crew and the commanding officer.
It was given the RAF aircraft code prefix "FN", which was often said to be an abbreviation for "First Norwegian" or "For Norway", the latter being the squadron's official motto (in Norwegian For Norge). The squadron badge was a Norwegian Viking sword and a British sword in saltire, bound together with a ring — symbolising the friendship between Norway and Great Britain.
Aircraft operated during RAF service
July–August 1941 Hawker Hurricane I & IIB
August–November 1941 Supermarine Spitfire IIA
November 1941-August 1942 Supermarine Spitfire VB
March–October 1942 Supermarine Spitfire IXB
October 1942-November 1945 Supermarine Spitfire IXE
The squadron was initially equipped with Hawker Hurricane Mk 1s, inherited from a Polish RAF unit. These had to be rebuilt before 331 Squadron could become operational, on 15 September 1941. It provided defence for northern Scotland, moving to RAF Castletown on 21 August and later to RAF Skaebrae.
On the 4th May 1942, the squadron moved south to RAF North Weald, having re-equipped with Spitfires in November 1941.
331 Squadron was joined by a second Norwegian unit 332 Squadron, also flying Spitfires. Together they were known as North Weald Wing and were part of the Allied air umbrella over the landing area in the Dieppe Raid, and later flying fighter sweeps and escort operations over occupied France and the Low Countries.
In November 1943, 331 and 332 Squadrons were transferred to the 2nd Tactical Air Force and became known as No. 132 Airfield; later No. 132 Wing.
Following fighter bomber and tactical air superiority operations, connected to preparations for D-Day and the actual landings in France, the squadron moved to Caen, Normandy, in August 1944. From September onwards, 132 Wing participated in the Liberation of Holland and provided air support for the crossing of the Rhine.
On 24 April 1945, the squadron was transferred to North Weald and later to RAF Dyce in Scotland, where 331 and 332 Squadrons converted to Spitfire Mark IXe and Mk XVI.
Following the end of the war, the wing flew to Norway and on 21 September 1945, 331 Squadron was officially disbanded as an RAF unit, with control passed to the re-formed Royal Norwegian Air Force (RNoAF).
Between them during the war, 331 and 332 Squadrons scored 180 confirmed destroyed, 35 probables and more than 100 damaged. Combined losses were 131 aircraft lost with 71 pilots killed.
In honour of the achievements of the Second World War squadrons, the RNoAF has maintained RAF squadron names, including a 331st Fighter Squadron, now flying F-16s and based at Bodø Main Air Station.