The squadron, as part of No. 12 Group, first saw combat in May 1940 during the evacuation from Dunkirk, in battles which exacted a heavy toll on both pilots and aircraft. Thereafter No. 74 (F) Squadron served successfully through the Battle of Britain, being heavily involved throughout June and July. On 11 August, the squadron flew four sorties and by the end of the day had claimed 24 victories and 14 damaged. On 14 August, No. 74 (F) Squadron was posted to RAF Wittering for rest and shortly after moved onto RAF Kirton in Lindsey and then onto RAF Coltishall, Norfolk. It was here at Coltishall in September 1940 that the squadron replaced their Spitfire Mk.Is with the Mk.IIa. The squadron moved back south to RAF Biggin Hill in October for the end of the Battle. Between November and December 1940, No. 74 (F) Squadron destroyed 38 enemy aircraft.