A tight curve is a great test of a pilot's skill because as G increases, so does the stalling speed. In a tight turn, the aircraft is on the threshold of stalling and will teeter as the pilot loses and then regains control. Note the gravity exerted. A pilot of average fitness begins to black out at only 4G or 5G. At 9G the average airframe begins to break up, for the wings are taking the strain of nine times the weight of the aircraft. And the stalling speed is by then very high: for example, a Spitfire will have a stalling speed of over 250 mph.

Note the way in which neither wingspan nor wing loading is decisive in the matter of the tightest turning circle.]

Some of the Spitfires were lost in spins, so pilots were told to avoid this manoeuvre. The Messerschmitt suffered no such vice; there was no problem getting out of a spin and it never went into a flat spin.

On the ground the Messerschmitt was 'a pig'. It had terrible forward vision, and whereas you could slide the Spitfire's hood back, the cumbersome hinged cover of the Messerschmitt had to be closed for taxiing. The lightness of the airframe made the Messerschmitt dance all over the place when running over uneven ground. It was easy to put a wingtip onto the grass.

Spitfires seldom broke up in the air. In those rare cases where too much stress was put on the airframe, those beautifully thin Mitchell wings were the first part to go. The Messerschmitt wings were also a weak part structurally but the tail was even weaker.

In 1940 a pilot was expected to judge the amount of stress he was putting on his airframe; there were no instruments to tell him how near he was to break-up. In practice this meant that most pilots were very careful to keep well within the limits, and few aircraft were stressed to breaking point. The arguments about which type could out-turn which are usually no more than a reflection of the recklessness of the opponents a man had flown against.

And just as every squadron had pilots who would fly to 'ten tenths' of their aircraft structural strength, so every squadron on both sides had dud aeroplanes that were to be avoided and unusually good ones that were often claimed by those with rank or influence. And these pilots got the best riggers, fitters, and armourers too. The green pilots got the slack and inferior ground crews, and the inferior aircraft, and they were shot down. The squadron diaries record the way in which men who scored a victory or two dramatically increased their chances of survival.

As the 1920s became the 1930s, the politicians who had pursued a popular course of denying tax-payers' money to the military now found it politically expedient to spend a little money on defence against the bomber. Pacifism as a way of cutting taxes was one thing, but getting bombed was something else. Bombing killed voters; precision bombing killed politicians.

In 1934, a vast sound-location device was built on Romney Marshes. It was 25 feet high and 200 feet long. It did not detect approaching RAF bombers until they were eight miles away, and could give no information about altitude or bearing. And it did not work at all unless the aircraft were on the axis of its fixed curve. As a final absurdity, this expensive manifestation of official lunacy faced France, Britain's closest military ally.

Grasping at straws, a newly formed scientific committee under Henry Tizard asked Robert Watson-Watt (a plump, pedantic radio expert of the National Physical Laboratories) whether there was any chance of developing a 'death-ray' that was a popular ingredient of spy fiction of the period. That meant a weapon that would emit damaging radiation to stop engines, or kill, maim, or disable air crews, or perhaps weaken an aircraft structure. The answer was an unequivocal no, but reasoning that even if a death-ray was possible, the defences would still need to know where to aim it, Watson-Watt added a final paragraph on the subject of detection. He wrote:

Meanwhile attention is being turned to the still difficult but less unpromising problem of radio-detection as opposed to radio-destruction, and numerical considerations on the method of detection by reflected radio waves will be submitted if required.

So, at the committee's first meeting in January 1935, they asked Watson-Watt to submit his ‘considerations’. Air Marshal Hugh Dowding (at the time the Air Council's Member for Research and Development) called for a demonstration of this reflection theory. Using existing equipment, an ordinary BBC broadcast as the beam, and an RAF Heyford bomber as the enemy aircraft, the experiment was set up immediately. In spite of a thousand cautions from Watson-Watt that this makeshift arrangement might well prove a fiasco or perhaps because of them the cathode-ray tube's flickering response was far beyond expectations.

The demonstration was set up in a field, using mobile apparatus. Watson-Watt — an opinionated Scotsman in baggy suit and granny glasses — took his nephew along for the ride but because the experiment was such a closely guarded secret he left him at the roadside nearby.

The successful demonstration generated great enthusiasm and moved the conversation immediately from long distance detection which now seemed well within their grasp to the possibilities of precision radar accurate enough for aiming anti-aircraft guns. Watson-Watt remembers no excitement or elation but he admitted driving his car a considerable distance towards London before remembering that he had left his nephew behind.

Between 1876 and 1903, three inventions changed the world more drastically than man had ever done before. First, Dr. Nicholaus Otto built a gas engine that was improved by Daimler in 1885 so it could propel a wheeled vehicle. Only two years later, Heinrich Rudolf Hertz made sparks into an electric wave, and by 1897 Guglielmo Marconi used those electric waves to send a wireless message nine miles. Now the world had only to wait until 1903 for the Wright brothers to combine an internal-combustion engine with a glider.

The internal-combustion engine, the aeroplane, and wireless transformed war even more than gunpowder or steam-power had done. But during the twentieth century only one great battle has been fought and decided by these three inventions alone, and that was the Battle of Britain.

Hertz's invention had been developed into radio-telephony, with which the fighter pilots spoke to ground control and to each other, into HF/DF (high-frequency direction-finding) for friendly fighter location but, most vitally, into the technique of radar. Hertz himself had been aware of the way in which his radio waves reflected from solid objects, and had even demonstrated it. Very soon afterwards, a German engineer proposed this technique as a way for ships in fog or darkness to 'see' each other and avoid collision.

But there were great problems still to be overcome. If the radio transmission is likened to a shout, and its return to an echo, it was not known how to make the shout loud enough to carry very far, or short enough to separate shout from echo.

The Americans Gregory Breit and Merle Tuve contributed short-pulsed transmissions, and showed how they could be bounced back from layers of the ionosphere. Curiously, it was six years before Professor E. V. Appleton, the distinguished English physicist, used radio to establish the height of the ionosphere, and of another layer that was named after him. Appleton was showered with honours and, along with at least a dozen other people, he is often named as the father of radar. However, Appleton's radio probes of the ionosphere were based upon a frequency-change method, and had no resemblance to the later radar techniques. Nor was he able to measure the distance from earth of any selected part of the ionosphere. His approximations vere good enough for physicists but not accurate enough for gunnery.