The Gloster F.9/37 (or 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. Although it was initially favoured, the Gloster F.9/37 was not able to compete with other, more advanced designs.
A prototype (military serial number L7999) with 1,060 hp Taurus T-S(a) radials 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 a reduced performance. A second prototype (L8002) with 880 hp Rolls-Royce Peregrine I liquid-cooled in-line engines flew on 22 February 1940, albeit with no overall improvement in top speed.
