During 1938, by which point British authorities were preparing for the likelihood of a major conflict, the Air Ministry issued a pair of specifications calling for naval fighters, a conventional and a "turret fighter". The performance requirements for both was to be able to attain a speed of 275 knots while flying at and carrying an armament, for the conventional fighter, of eight Browning machine guns or four Hispano cannon. This aircraft would replace the Fairey Fulmar, which had been viewed as an interim design. These specifications were updated during the following year, while several British manufacturers tendered their ideas. Further changes to the official specification followed, such as the turret fighter specification being eliminated entirely, while a modified specification was issued to cover single and dual-seat fighters capable of respectively. Fairey offered designs that could accommodate either a single or twin-seat arrangements, either powered by the Rolls-Royce Griffon engine, or combining a larger airframe with a Napier Sabre engine. After consideration of the manufacturer's responses, Specification N.5/40 replaced the earlier specifications. Due to the necessity of navigating over open sea, it was decided to opt for a two-seater aircraft alone. For defence of naval bases, a separate single seater design would lead to the Blackburn Firebrand.