In August 1944, the first F.3 prototype flew; early F.3 production aircraft were still fitted with the Welland engine as the Derwent engine's production line was only just starting at this point.
I august 1944 fløj den første prototype af F.3; tidlige F.3 produktionsfly var stadig udstyret med Welland motoren, eftersom produktionslinien for Rolls-Royce Derwent motoren endnu var under opstart.