In two days Dowding had lost another ten fighter squadrons, and was now down to about half of the strength that was considered a dangerous minimum. It is in the context of these events that the bitter accusations of French High Commanders (that Churchill betrayed the alliance by denying France RAF fighters) must be considered.

Undoubtedly Churchill was extremely moved by the pleas of the French politicians and by the great and sudden tragedy that France was suffering. To what extent he wanted to reassert his command of the War Cabinet, and whether he took an instant dislike to Dowding as he had to certain other military commanders or what other motives he had, remains unknown. Churchill's memoirs only add to the mystery. He does not refer to Dowding's attendance at No. 10, and did not acknowledge any urgent warning. On the contrary, Churchill wrote, "Air Chief Marshal Dowding, at the head of metropolitan Fighter Command, had declared to me that with twenty-five squadrons of fighters he could defend the island against the whole of the German Air Force, but that with less he would be overpowered."

This was nonsense. There were witnesses, there was the graph of Hurricane losses, and there was the letter that Dowding — ever distrustful of politicians — wrote immediately after the meeting. Without these, history might have recorded another instance of a politician being badly advised by his experts.

Dowding's fears about fighters sent to France proved well founded. When the final figures came in, the losses caused to the 261 Hurricanes sent to support the British army were grave. Only 66 of these got back to England.

With German bases facing the British coast from northwestern France to southern Norway, Dowding arranged his fighter squadrons to meet the inevitable attack.

Military experts were still incredulous that Panzerkorps Reinhardt had moved tanks through France forty miles in one day. Now began a battle in which units would move at 300 mph.

To fight such battles Dowding had quartered Britain into Fighter Groups. Each Group had a commander and a staff who worked at a large operations table, over which girls, using croupier's rakes, moved coloured counters.

Depending on the generalship of these commanders, and their Operations Room staff, the battles would be lost or won. They would have only minutes — seconds sometimes — in which to decide which coloured counters might be a feint attack. Ordering fighters into the air too late made them easy prey for the Germans above them. Scrambling too few squadrons might lose a battle, scrambling too many meant undefended towns or, worse still, fighters refuelling so that a second wave of bombers destroyed them on the ground.

To all these calculations were added the problems of cloud that hid the raiders at certain heights and weather that might shut in British bases while leaving cross-Channel ones operative. Anti-aircraft gun batteries and balloon barrages had to be deployed so that they played their part against the enemy.

And while these great battles raged across the tables of the Operations Rooms, the Sector Controllers spoke with their fighter pilots 20,000 feet above. They watched the counters converge and heard the pilots as they wheeled and fired and cursed and died. Never before had there been battles like these.

The history of invention often shows a pattern of acceleration, in the later stages of which inventors take it for granted that some other element they need will miraculously appear. This is particularly true of inventions applicable to warfare, stimulated as they often are by politics, economics, or predicament.

Before the First World War, for instance, the oil-fired boiler, the turbine, the fifteen-inch gun, and armour had together produced a revolution in battleship design: the Queen Elizabeth class.

In the nineteenth century, percussion caps, bolt action and a needle firing device contributed to a new kind of infantry rifle that then remained virtually unchanged for a hundred years. And Hiram Maxim evolved a design for a machine gun that would never have functioned except that in the final stages a new explosive was developed. Only then did he have enough bore and chamber pressure for a practical gun.

So it was with the metal monoplane fighters that fought on both sides during the Battle of Britain. In the 1930s two-gun, wood-and-fabric biplanes not very different from the aircraft of the First World War suddenly gave way to a totally different sort of flying machine. Three designers: Willy Messerschmitt, Sydney Camm, and Reginald Mitchell led the radical change. The result was the Bf109, Hurricane, and Spitfire.

The biplane was as old as the history of powered flight. The Wright brothers had chosen two wings, one above the other, for the same reason as the other experimenters: it gave double the amount of wing for any given size of machine, and the wings could be braced together to form a lightweight but rigid box. But doubling the wing area, by making a biplane, did not produce double the amount of lift. Wingtips were a primary source of drag. There is also an effect called 'biplane interference' which is the way that each wing's airflow disturbs that of its neighbour. In the 1920s and 1930s aircraft designers built curious-looking machines in which little leg-like struts held the fuselage above the lower wing. But, no matter how far apart the designers placed the wings, these troubles remained.

Mankind discovered the secret of flight as soon as he stopped flapping his home-made wings long enough to understand that it was all a matter of decreasing the air pressure upon a wing's upper surface. This realization came long before the Wright brothers. The most important work was that of a German, Otto Lilienthal, who made more than a thousand flights in gliders of his own design and studied the way in which certain curved wings — aerofoil sections — gave better lift than others. By the end of the nineteenth century, man still could not build a powered flying machine but the theory was den ned wind-tunnels were in use, and airflow had been photographed. It became more and more obvious that the problem was to get enough air flowing fast enough across the wing to decrease the air pressure there and so lift — or one could almost say suck — the wing upwards.

The Wright brothers went to live at Kitty Hawk, North Carolina, because there was a constant wind off the sea This gave them an effective airspeed of about 20 mph, even when their glider was not moving forward. This was exactly the benefit they needed while they perfected a glider design suitable to hold an engine. They could not use a motor-car engine, because all contemporary ones were too heavy by far. It was their assistant, an unsung hero named Charles Taylor, who took only six weeks to build a light weight petrol engine from scratch. He even made the camshaft from a solid block of metal. His engine was based upon an earlier gas-engine design by Lenoir but that does not alter the fact that Taylor was more important as a pioneer of powered flight than were the Wright brothers.

There had been other aircraft that flew. As early as 1848 John Stringfellow had built a steam-powered flying machine, and demonstrated it with enough success to win a prize. But Stringfellow's machine could not take the added weight of a man.