Pre-dated by the Boulton Paul P.92, which only ever flew as a half-scale prototype, but which was designed to meet the F.11/37 specification for a turret armed fighter aircraft. As designed the turret itself was a shallow dome, 13 ft in diameter, built into a thickened centre wing section and mounting four 20 mm cannon. The contract for the two full-scale prototypes was cancelled in May 1940, but the half-scale prototype that was ordered in May 1939 was completed and flew in early 1941. Wikipedia notes that while specification F.11/37 was suspended, the idea of a four cannon turret was relevant to B.1/39.