No. 421 Squadron RCAF was a unit of the Royal Canadian Air Force. It was the last RCAF fighter squadron to be formed in the UK during World War II. Initially established at RAF Digby in April 1942 with Supermarine Spitfire Mk VA, the squadron moving to RAF Fairwood Common in May and received Spitfire Mk VB. During 1942 the squadron was under 10 Group and flew its mission from RAF Warmwell, RAF Bolt Head, RAF Ibsley, RAF Zeals and RAF Charmy Down.