The fact that the code breakers at Bletchley had cracked the codes used to encrypt the messages sent to and from the German high command was possibly the most closely guarded allied secret of the war. Little or nothing emerged about the work at Bletchley until the 1970s. This was partly because the British started making and selling encryption machines such as Enigma and Lorenz, and did not want their customers to know that their output was breakable.
The code-breaking was done by hand for two years until the value and volume of Tunny traffic rose to the point where the government allowed Bletchley Park to spend some money to automate the process.
Max Newman, head of the so-called Newmanry or machine section of Station X, proposed using Alan Turing's (father of modern computing) pre-war work on computer theory to build a machine to speed up decoding. An initial machine, which is currently being rebuilt by the National Museum of Computing, the (Heath) Robinson, proved unreliable because the paper tape it used to input data broke often.
Bletchley Park called in Tommy Flowers, a Post Office engineer who specialised in telephone exchanges. Roberts says Flowers was briefed by Newman, Tutte and Turing as to what output they wanted.
Flowers proposed, to great scepticism, a machine that could replicate the Lorenz in electronic format. He was given two years to develop the device.
"When he told colleagues he was going to use valves, they said 'you're mad, because they are not reliable, and they'll let you down'," says Jerry Roberts, the last surviving member of the Testery, part of Station X. "He solved that with the very simple idea of never turning them off."