Secret few broke wartime Enigma

The words would resound down the years, an eloquent tribute to the men who won the Battle of Britain.

Never in the field of human conflict, pronounced the country's bulldog wartime Prime Minister, Winston Churchill, was so much owed by so many to so few.

He was referring to the dashing pilots who defended Britain from German attack. But in the years to come he might have talked about a more unlikely group of heroes if he had been able to officially acknowledge their existence.

For the truth is that the war was won not only by those on the beaches of Normandy and beyond. Victory was also the work of a bunch of eccentric geniuses based at a Tudor-Gothic mansion at Bletchley Park in Buckinghamshire, known to the War Office as Station X.

Station X was home to the cryptanalysts, or codebreakers, who deciphered intercepted German signals. These communications were at the heart of Hitler's blitzkrieg and co-ordinated the U-boats that stalked Allied shipping.

The teams had the Herculean task of breaking Enigma, the seemingly impenetrable German code. And, although their efforts brought to an end the carnage being wrought on merchant shipping their work remained secret until 30 years after the war's end.

Their achievements are the subject of Enigma, a film that opens next week.

Based on the novel by former British journalist Robert Harris, and starring Kate Winslet, it manages to dramatise the story of the codebreakers without dumbing it down or romanticising it into cheap multiplex pap.

And according to one who was there [see story alongside] it is very accurate.

The way Enigma worked, not to mention the often mind-bending detail of the way it was cracked, could fill a book. Indeed it has filled several, with Simon Singh's excellent history of cryptography, The Code Book, published by Fourth Estate, giving a brief and readable rundown.

Enigma was a code produced by a machine that looked like a cumbersome typewriter. When the keys were hit letters were encrypted twice over, once by a plugboard arrangement and once by a series of scramblers, which constantly changed position during encoding so that the plaintext letter's coded equivalents differed each time they appeared.

If the sender and receiver began with the same settings, decoding was mechanical, but if the starting set-up were unknown, it was impossible to find it without trying some 159 trillion settings.

Building on work undertaken by Polish cryptanalysts between the wars, the Bletchley Park team busted Enigma.

They were a bizarre bunch, including mathematicians, linguists, chess and bridge champions and even an authority on porcelain. Many were recruited after having demonstrated their ability to solve the Daily Telegraph crossword in less than 12 minutes.

And their Bletchley bosses, all military men, were often exasperated by the scruffiness of the professor types. Churchill himself, on one of several visits, grumbled to the head of the Security Intelligence Service that "I told you to leave no stone unturned [while recruiting], but I did not expect you to take me so literally".

The heroic stories had a tragic sequel. Foremost among the cryptographers was Alan Turing, a brilliant mathematician who, in the 30s, had crossed intellectual swords with Wittgenstein and Bertrand Russell.

It was Turing who worked out a way of drastically limiting the number of scrambler settings which needed to be tested and, building on a hypothetical device he had designed, which is the forerunner of the modern computer, he developed an electro-mechanical number-cruncher, called a bombe, which noisily checked thousands upon thousands of scrambler settings.

The path to victory was strewn with obstacles. When the Germans changed their method of communicating the daily code-key, it put the codebreakers back to square one.

Both novel and film depict dramatically the white-knuckle brinkmanship of military planners who used a convoy of merchant shipping as a sacrificial lure for a fleet of German U-boats in the knowledge that, just before they attacked, they would transmit their positions, giving code-breakers a desperately needed coded version of their known positions - from which to deduce the essence of the new Enigma.

Turing might, in another age, have become a household name. But after the war, he naively revealed his homosexuality to police officers while reporting a burglary.

Prosecuted for gross indecency, he was publicly humiliated and forbidden to work in his beloved areas of research.

Deeply depressed, he committed suicide by biting into an apple dipped in cyanide.

Some have suggested that his contribution to modern computing is celebrated by the famous bitten apple logo of a popular computer brand. But the company's head office has never heard of the notion.