The Gloster F.9/37, also known as the Gloster G.39, was a British twin-engined design from the Gloster Aircraft Company for a cannon-armed heavy fighter to serve with the Royal Air Force, planned before the Second World War. The F.9/37 was rejected in favour of other designs. A development of the F.9/37 as a night fighter, for a new Air Ministry Specifications F.29/40 – known unofficially as the Gloster Reaper – was dropped so that Gloster could concentrate on existing work and on the nascent British jet projects.