No longer would fighter airframes be braced by interior cross-wires. Now the metal fuselages would have space for additional equipment.

Plane's wings had to be designed to take all stresses and buffeting of high-speed flight and centrifugal force without tearing off at the roots. Biplanes had bracing wires and struts to hold wings and fuselage together, but the monoplane's wings had to have enough internal strength to withstand the strain, while providing enough space inside the wing to take not only the retracted wheels and undercarriage but also machine guns. The guns could not be in the thick roots of the wings, for they must fire outboard of the propeller (so that they could fire at the maximum rate, rather than be slowed by synchronizing gear).

The RAF experts wanted speeds in the region of 300 mph and a ceiling of 33,000 feet. Such speeds meant streamlining, and wheels that retracted into the wings meant all the complications of a hydraulics system. The cockpit had to be completely enclosed, without loss of visibility, and the hood must be made so that the pilot could slide it back easily, even at high speeds. Yet these new machines would not be handled just by record-breaking experts. The average service pilot must be able to fly them, and land on a grass field no more than 1,250 yards long. That called for a slow landing-speed, without danger of stalling, and there would have to be reliable brakes on the wheels.

At the sort of speeds the new monoplanes would fly, there could be no more wing-waggling, and hand-waving, to tell the formation what the leader wanted. The pilots must be able to talk to ground control, and talk to each other. Two-way radio meant high-frequency signals. There were other sciences too. Low landing-speeds meant split flaps on the wings. High ceiling meant oxygen for the pilot, and super-charging for the engine. And high-speed combat would grant pilots only a glimpse of the enemy. They would need better gun-sights, and guns that could deliver a fatal burst in just two seconds.

And the guns must be reliable, for if they were in the wings, the pilot would no longer be able to hammer a jammed round out of the breech. The RAF tried all the world's machine guns and then selected the Colt-Browning. It proved an excellent gun, with a stoppage rate averaging once in 15,000 rounds. When installed alongside seven other guns this stoppage rate was entirely acceptable.

Having decided to put eight guns into each fighter, the RAF required enough bullets to provide for a total of fourteen seconds of firing. So there had to be space enough, and strength enough, to carry 2,660 rounds.

The aircraft factories would have to retrain workers in the new skills of lightweight metal alloys, and they needed designers who understood the theories of stressed-metal construction. No longer would fighter airframes be braced by interior cross-wires: the strength had to be in the shell. This was the definition of monocoque, and this type of airframe became more and more necessary as ancillary equipment was packed into the fuselage.

Metal aircraft were not a new idea. Professor Hugo Junkers — perhaps the greatest genius of his period of aircraft design — had built an all-metal, cantilever-wing monoplane as early as 1915. In 1917, Dornier had built a metal seaplane and then a biplane fighter. The British designer Oswald Short progressed from the box-like German designs to a streamlined circular-section Silver Streak in 1919. But these isolated examples were not much help with the new designs. There was nothing in America that would help either. American all-metal monoplanes were large, passenger-carrying aircraft, such as the magnificent Boeing 247, a twin-engined design that set the pattern for such airliners for the next quarter century, including the remarkable Douglas DC1 which followed shortly afterwards. But high-speed monoplane fighters needed extreme altitude, extreme speed, and an ability to withstand the G of tight turns and steep pull-outs. The British and German designers were on their own.

The Hurricane

Like the Spitfire, the Hawker Hurricane began with Air Ministry specification F.7/30 for a fighter to replace the Bristol Bulldog biplane fighter then in RAF service. Sydney Camm was Chief Designer of Hawker Aircraft Ltd, which had evolved from Sopwiths, one of the world's most famous manufacturers of First World War fighters. Camm submitted a design for a biplane and a monoplane. Both were rejected. Of the monoplane, an official historian wrote, it "was too orthodox even for the Air Ministry."

Sydney Camm was a tall, dark man, slightly bent in posture from years of working at drawing boards. His nose was patrician and he had the sort of prominent chin that is said to go with determination.

The navy's aviation requirements dominated US fighter design. The navy wanted lightweight, short-take-off fighters suitable for carrier operations. And that meant biplanes with air-cooled radial engines.

The only comparable fighter designs anywhere in the world in January 1940 were the French Dewoitine 520S and the Japanese Mitsubishi A6M2 Zero-Sen but less than ten of the former had been delivered by this time, and the latter had not even been officially accepted.

Even less in evidence was any power unit that could compare with the Daimler-Benz 601 or the Rolls-Royce Merlin. That's why the British purchasing commission that went to the USA in 1940 had to specify its own requirements to US airframe manufacturers, and have Merlins built there under licence. In time, this combination became the P-51 Mustang fighter.

Hawker Fury

Now, given full support by Hawker's, he began to design a fighter monoplane as a private venture, ignoring the Air Ministry specification. For reasons of economy, he used as much as possible of Hawker's tools and jigs. And all the time, he was keeping one eye upon the work that Rolls-Royce were doing on their new engine PV 12.

So by the time the Air Ministry had decided to issue a more advanced specification, Camm was ready with his design, and about to build a prototype of what he called a 'Fury Monoplane' — a development of his very successful Hawker Fury biplane fighter.

It was a project he had long talked about. In the summer of 1935, Camm, now 38 years old, and with ten years as Chief Designer of Hawker's, received Air Ministry specification F.I0/35. The major remaining difference between this specification and the fighter he was building was the number of machine guns. Rather than delay the first flight of his prototype, he had another pair of wings made. When these new wings were fitted, in the summer of 1936, the Hawker Hurricane was born.

So the Hurricane was a monoplane version of the Hawker Fury. It used the same patent construction: a wire-braced framework of metal tubes. Round this was built a wooden frame, of formers and stringers. Fabric was stretched over the outside. At first not even the wings were of stressed-metal construction, but metal ones were designed before full-scale production started.

The Hurricane was not a monocoque construction. It was an old-fashioned wood-and-fabric machine, stiffened by a metal-tube framework. It was a half-way house between the old biplanes and the new Spitfires and yet there were certain advantages to such construction. The exploding cannon shells, which did terrible damage to metal skin, had less effect upon any sort of girder work (in the same way that bombs so often failed to topple the radar towers). And the RAF had very few men who understood the complexities of stressed-metal construction, but its airframe fitters and flight mechanics had spent their lives servicing, and rigging, aircraft like this. When the fighting started, many seriously damaged Hurricanes were repaired in squadron workshops.