Only the navy and a handful of fighter planes held the invaders at bay.
On August 28 six of Britain’s top scientists and engineers set out from Liverpool on the liner The Duchess of Richmond. Led by Sir Henry Tizard, rector of Imperial College, London, they were about to make a hazardous Atlantic crossing. With them was perhaps the most precious cargo of the war – a black deed-box containing Britain’s most valuable technological secrets.
They included a device called the “cavity magnetron” which was to be the Holy Grail of the quest to secure Britain’s air defences against the Luftwaffe’s night raids. British scientists had invented it but with industry on its knees they needed someone to manufacture it quickly and in bulk.
Tizard’s mission was to give the secret device to the Americans in the hope they would release the resources to develop it.
Since the early Thirties it had been clear that Britain – as a small with heavy concentrations of population and industry – was more vulnerable to aerial bombing than any other country. Prime Minister Stanley Baldwin had
predicted gloomily that “the bomber will always get through” but Tizard believed that something could be done.
In 1935 he was named head of a committee to find scientific ways of strengthening our air defences. One option was to use radio waves to detect approaching bombers.
Tizard gave crucial backing to the development of this “radar” technology. By early 1937 workmen were busy building a chain of stations whose 300ft towers would eventually stretch from the Isle of Wight to the Firth of Tay.
With an early-warning range of 100 miles this radar system gave our fighters time to get off the ground (where they would have been sitting ducks) and into the air where they could engage the attackers. The system had a good chance of repelling daylight onslaughts.
The problem, Tizard predicted, was that the Luftwaffe would then turn to night bombing, when its planes would be harder to shoot down. What was needed was airborne radar that would allow pilots to intercept the enemy without
visual contact. The equipment would have to weigh no more than 200lb, fit into a space of no more than eight cubic feet and run off a maximum power output of 500W – as well as withstand the plane’s vibrations.
Scientists determined that radar would work best with a narrow beam, which meant shortening the wavelength to something measured not in metres but centimetres. Working in secret at Birmingham University, two scientists called John Randall and Harry Boot came up with the solution.
Small enough to hold in the palm of the hand, the cavity magnetron was a round, copper block drilled with six holes with a tiny slot running down each hole. Surrounded with a powerful magnetic field and fed with electrical power, the electrons in the cavities would swirl – just as air swirls in a whistle – to form a high-power “microwave”.
Suddenly, instead of requiring masts hundreds of feet high, radar could be fitted into the nose of a twin-engined fighter. But Britain needed allies with the manufacturing clout to get the device on to the front line. The US was the obvious candidate but there was mistrust between the two powers and America was reluctant to enter the war.
For some years Britain had been trying to trade military secrets withthe US – largely in a bid to get hold of the Norden bombsight, a device which the Americans claimed could “drop a bomb into a pickle barrel”. But neither side’s military were prepared to give up secrets in return for an unknown quantity.
Tizard’s revolutionary approach – initially opposed by Winston Churchill who had become Prime Minister in May 1940 – was to give Britain’s secrets away. He was convinced this was the only sure way to access America’s enormous development and manufacturing resources. After winning Churchill’s approval Tizard met President Roosevelt at the White House and War Secretary Henry Stimson, who thought him “a very nice and sensible British scientist”. He also met teams of defence scientists and played his trump card.
Bell Telephone Labs and General Electric had developed equipment to receive wavelengths as short as 10cm but as the scientists admitted, they couldn’t generate anywhere near enough power to transmit at that wavelength.
At this point one of Tizard’s team recorded: “We quietly produced the magnetron and those present were shaken to learn that it could produce a full 10 kilowatts of pulsed power at a wavelength of 10 centimetres.” That was roughly 1,000 times the power any US lab had been able to generate with much larger tubes. No wonder the Americans were staggered.
After that co-operation fell into place. By October Bell Labs had produced 30 magnetrons and by the end of the war it had made more than a million. The device enabled warships and aircraft to carry radar that gave the Allies a crucial military edge.
Decades years later US scientist Luis Alvarez said of the magnetron: “A sudden improvement by a factor of 3,000 may not surprise physicists but it is almost unheard of in engineering. If automobiles had been similarly improved, modern cars would cost about a dollar and go for a thousand miles on a gallon of gas.”
Tizard, who became chief scientific adviser to the Ministry of Defence after the war and died in 1959, wrote: “When I went to Washington in 1940 I found that radar had been invented in America at about the same time it had been invented in England.
“We were, however, a long way ahead in its practical application to war. The reason for this was that scientists and serving officers had combined before the war to study its tactical uses. This is the great lesson of the last war.”
To pre-order a copy of the book Tizard Mission by Stephen Phelps (Westholme Publishing) at £18.99 published February, send a cheque or PO made payable to Express Bookshop to: Phelps Offer, PO Box 200, Falmouth TR11 4WJ or tel 0871 988 8367 or go to www.expressbookshop.com. UK delivery free. Calls cost 10p per minute from UK landlines.