The Gloster F.9-37, also known as the Gloster G.39, was a British twin-engine 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.
Gloster had designed a twin-engined turret-fighter for specification F.34/35 but the single-engined Boulton Paul Defiant for F.9/35 was seen to cover both requirements and the F.34/35 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 George 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.
Intended for dispersed production by semi-skilled labour, the structure broke down into sub-assemblies.
A prototype (military serial 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 (580 km/h) 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”.
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 reduced its performance.
A second prototype (L8002) with 880 hp Rolls-Royce Peregrine I liquid-cooled, inline engines flew on 22 February 1940; it proved capable of 330 mph (530 km/h) at 15,000 ft (4,600 m).
