On 15 July 1941 Air Marshal Sir Sholto Douglas promised to form an RAF Squadron with only Belgian pilots and mechanics. Confirmation from the Air Ministry followed on 1 November 1941. The Squadron would be stationed at RAF Valley, Anglesey.

The Belgian Military Attaché immediately created a list of 39 pilots that were either dispersed over other Squadrons or were still in the OTU. He also proposed to make Le Roy du Vivier Squadron Leader, but this proposal was not accepted and the British Squadron Leader J M Thompson D.F.C. of 131 (County of Kent) Squadron RAF received the title. 

The Squadron formed at Valley, Anglesey, North Wales, on 12 November 1941 with the C.O. and a nucleus of 12 Belgian pilots from 131 (County of Kent) Squadron, and was funded almost completely by money rolling in from the raw materials (copper, etc) that were coming from the Belgian colonies (Congo, Ruanda and Burundi) and used by the British war industry.

12/11/41 

No. 350 (Belgian) Squadron formed at R.A.F. Station, Valley (Station Commander, W/Cdr. J.C.W. Oliver, D.S.O., D.F.C.) on 12th November, 1941 from Belgian Flight, 131 Squadron and various other Belgian pilots in Squadrons in the Command. Squadron to be Commanded by British Squadron Leader.
Personnel to be comprised so far as possible of Belgian Nationals.
Squadron Leader J. M. Thompson, D.F.C. appointed to Command from No. 131 Squadron.

16/11/41 

Squadron Leader J. M. Thompson, D.F.C. posted in from No. 131 Squadron to Command No. 350 (Belgian) Squadron.
Pilot Officer/Acting Flying Officer H. Robinson posted in from No. 131 Squadron for duties as Adjudant, No. 350 (Belgian) Squadron.
Pilot Officer L.M.V. Peters posted in from No. 124 Squadron for flying duties.

17/11/41

Flying Officer/Acting Flight Lieutenant H.A.C. Gonay posted in from No. 131 Squadron for duties as flight commander in No. 350 Squadron. Pilot Officers X.L.A. Menu, M.J. Plas, J.J.L. Smets, G.F.D. Deltour, J.V. De Puysseleyr, A.H.A. Plisnier, Sergeant Pilots Seydel G.M.H., Ester J., and Harmel L.J. posted in from No. 131 Squadron for flying duties. Sergeant Vanlerberghe J.L.E. posted in for flying duties from No. 122 Squadron.

18/11/41

Sergeant Blairon J.A. posted in from No. 74 Squadron, Sergeant Van Moffaort H.E.R. posted in from No. 124 Squadron and Sergeant Alexandre R.A.G. posted in from No. 124 Squadron for flying duties. 

19/11/41 

Sergeant Heimes L. posted in from No. 122 Squadron for flying duties.

20/11/41

Pilot Officer A.M.J. Custers posted in from No. 43 Squadron for flying duties. Pilot Officer J.A.M.J.G. Carlier posted in from No. 135 Squadron for duties as flight commander in No. 350 Squadron.

21/11/41

Pilot Officer C.F.E. Regnier posted in from No. 56 O.T.U. for duties as Squadron Engineer Officer after attachment to No. 74 Squadron for period 14th to 21st November.

23/11/41

Sergeant Hansez J.L. posted in from No. 122 Squadron for flying duties.

24/11/41

Notified by No. 3 Delivery flight, Hawarden that five Spitfire IIA Aircraft would be delivered. Weather later deteriorated. One pilot of Delivery Flight crashed near Menai Straits and was killed; the aircraft was burnt out. Sergeant Claeson, posted to No. 350 (Belgian) Squadron, on attachment to No. 3 Delivery Flight pending his arrival with aircraft, crashed off the runways and was seriously injured; the aircraft was totally wrecked. Three remaining aircraft did not attempt journey.

25/11/41

Spitfire Aircraft Mark IIA Nos. P7613, P8020 and P8652 received from No. 610 Squadron and delivery by Ferry Pool pilots.
Pilot Officer R. de Wever reported in on the expiration of 7 days leave, posted from No. 131 Squadron for flying duties.

26/11/41

Pilot Officer H.A. Picard reported in from attachment to R.A.F. Station, Atcham. Posted in from No. 131 Squadron for flying duties.

27/11/41

Lecture given to Squadron pilots on Operational tactics by Squadron Leader D. Sheen, D.F.C. No. 9 Group Tactics Officer.
Pilot Officer W.H. Evans posted in from Headquarters Fighter Command for duties as Squadron Intelligence Officer.

28/11/41

Spitfire Aircraft Mark IIA Nos. P7976, P8702 and P7826 received from No. 74 Squadron.

30/11/41

Strength of Unit:-          Officers – British  3.       Belgian 13.
                                   Airmen – British  75.     Belgian 25.

 J. M. Thompson

Squadron Leader

Officer Commanding

No. 350 (Belgian) Squadron

R.A.F. Valley