Why the British cancelled this heavyweight superfighter in World War II

Faster, better-armed and longer-ranged than the contemporary Spitfire, the Gloster F9/37 was a superb machine that failed to enter production. We take a look at this seldom-discussed heavy fighter aircraft.

The Hawker Demon biplane fighter first flew in 1933. The same year the British Air Ministry released a requirement (F.5/33) for its replacement. They wanted a two-seat monoplane fighter equipped with a gun turret, the thinking being that aiming a turret is easier than aiming the whole aeroplane and allows a far greater field of fire. The Gloster Aircraft Company, masters of the biplane, responded with a twin-engined monoplane design powered by the Bristol Aquila radial engine (an abortive project but one which would lead to the Hercules,  Taurus, and  Centaurus). The Air Staff, rightly, were suspecting that the concept of F.5/33 was flawed, and so issued F.34/35 demanding an additional fixed forward-firing armament. Gloster adjusted their design accordingly, adding fixed guns, but Boulton Paul’s turret-equipped Defiant won an order, leaving the Gloster F.34/35 entrant out in the cold.

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A year later, a new requirement was issued, F.9/37. This called for a single-seat, twin-engine, long-ranged fighter with fixed guns. At last, it seemed that Gloster’s luck was changing. The work they had done for F.34/35 put them in an excellent position, and the deletion of the heavy draggy turret created a fighter design potentially capable of spectacular performance. Gloster identified two possible engines, the water-cooled inline Rolls-Royce Peregrine and the extremely light powerful radial Bristol Taurus. Prototypes powered by each were to be built and tested.

When the first prototype (L7999), equipped with Taurus engines, flew in 3 April 1939 it was the fastest British fighter ever flown*, reaching an impressive 360 mph at 15,000 feet. Each of the Taurus T-S(a) engines generated an impressive 1,050 horsepower. The F9/37 (also known as the Gloster G.39) immediately earned the confidence of its pilot. It was blessed with fine handling, light controls and a dazzling performance.

Gloster F9/37 L7999 rear view ground
Source: BAE Systems

 It was extremely manoeuvrable, a delight to take-off and land, and virtually vice-free. Its pilot enjoyed an excellent field of view and the aircraft was planned to pack a heavy punch in the form of two cannon and four machine-guns. 

It was also far faster than contemporary heavy fighters then in operational service such as the Potez 630 (264mph) – and marginally swifter than the Bf 110 (336 mph) which had an identical amount of installed power (the British aircraft was around 2500Ibs lighter at maximum weight).

*it is believed that the Whirlwind was yet to achieve this figure, though later would.

Gloster F9/37 2nd prototype (L8002)

The prototype crashed through no fault of the design and as it was repaired work on the Peregrine-engined variant was progressing. When the Peregrine prototype flew it proved mediocre, the top speed dropping to a still respectable but not earth-shattering 330mph. The repaired and re-engined first prototype flew again in 1940 with the lower-powered 900 hp Taurus T-S(a)-Ills also proved disappointing.

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 despite being superior to the Beaufighter and (even the Mosquito in some respects).

W.G. Carter’s proposed a single-seat heavy fighter based on the design but with Merlin engines for spec F18/40. Whereas the radar-equipped version was to be armed with four 20-mm cannon, the day version would also have an additional eight light machine-guns in place of the radar. This would not have been available until 1942.

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Why bother?

The Reaper was lower powered than either the Mosquito or Bf 110 of the time, with either the Taurus or the Peregrine (which would soon be unavailable anyway). A Merlin-engined version would have worked but at this time everyone wanted Merlins. Ultimately why bother with a lumbering great heavy fighter when you’ve got the Mosquito busy being shit-hot at everything and the fastest production aircraft in the world? Or if you want something slower how about the Beaufighter? Gloster had their hands full building Hurricanes, and then Typhoons, as well as working on the development on Britain’s first jet aircraft. Arsing around with a complicated and expensive twin to no great purpose probably didn’t look like a great idea when you had two perfectly good heavy fighter designs and single engine types were proving perfectly fine at being cannon armed. As with the Whirlwind, when the question was asked, ‘what is more useful one heavy fighter or two Spitfires?’ the answer usually favoured the latter, unless the aircraft in question was the superlative (and already active) Mosquito.

Gloster F9/37 L7999 in flight
Photo: BAE Systems

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