In April 1935, the Air Ministry released Specification F.9/35, which required a two-seater day and night "turret fighter" capable of at . The aircraft was to feature a clean design, concentrating its armament within a power-operated turret, and the accepted performance was to be only slightly beneath that of other emergent fighter designs of the period, along with a sufficient fuel capacity to allow it to perform standing patrols. In particular, the powered turret was to offer considerable flexibility, possessing both a 360-degree upper hemisphere field of fire and the ability to engage enemy bombers from a range of quarters, including below the aircraft itself. Specification F.9/35 had followed the earlier Specification F.5/33, which had sought a pusher design combined with a forward-set turret; F.5/33 had been unceremoniously abandoned as the proposals had offered little in terms of performance gains over existing fighters, and the corresponding Armstrong Whitworth AW.34 design which had been ordered was not completed.