Gloster F.9/37

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 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 would be able to concentrate on existing work and on the nascent British jet projects.

Design and development
Gloster had designed a twin-engined turret-fighter for specification F.34/35 but the single engine design from Boulton Paul (Boulton Paul Defiant) for F.9/35 was seen to cover both requirements and the F.34/55 design dropped. Less than two years later, F.9/37 for a "twin-engined single-seat fighter with fixed armament" was issued.

The F.9/37 was designed under the direction of W. G. Carter, his first for Gloster, to F.9/37 (hence the name) as a single seat fighter carrying an armament of four 0.303 in (7.7 mm) Browning machine guns and two 20 mm Hispano cannon in the nose.

A prototype (military serial number L7999) with 1,060 hp Bristol Taurus T-S(a) radial engines flew on 3 April 1939, and demonstrated excellent performance, its maximum speed of 360 mph being the best recorded by a British fighter at the time. Test flights revealed that the prototype was very manoeuvrable and "a delight to fly." However, after being badly damaged in a landing accident in July 1939, it was re-engined with 900 hp Taurus T-S(a)-IIIs in 1940, which resulted in reduced performance. A second prototype (L8002) with 880 hp Rolls-Royce Peregrine I liquid-cooled in-line engines flew on 22 February 1940, it proved capable of 330 mph (530 km/h) at 15,000 ft (4,570 m).

F.18/40 and F.29/40
Specification F.18/40, for a dedicated night fighter, with both nose- and turret-mounted guns, led to Gloster submitting a design based on the F.9/37, fitted with Rolls-Royce Merlin engines, a dorsal four-gun turret and Airborne Interception (AI) radar. This received support from the Air Staff who saw it as superior to the Bristol Beaufighter and the Air Ministry ordered one of the F.9/37 prototypes to be converted to the new specification as F.29/40.

Unofficially known as the "Gloster Reaper", it inherited the admirable handling characteristics of the F.9/37, and despite being judged superior to other designs, including turreted variants of the Beaufighter and de Havilland Mosquito, the Reaper was terminated. The project was terminated in May 1941, so that Gloster could concentrate on other work, especially its work on jet aircraft.