Secret Life of Bletchley Park - McKay Sinclair [43]
When first trying to envisage the form of such a machine, Turing thought of typewriters, how they were built to carry out a certain sort of function. According to his biographer Andrew Hodges, he had in his head an idea of a super-typewriter: a machine that could identify symbols; that could write, but could also erase. A machine that could be configured in many ways to carry out many tasks, and yet would be automatic, requiring little or no intervention from a human operator. His argument was that any calculation that a human could perform, a machine could perform as well.
The bombes were not Universal Turing Machines. Far from it. Nor were they an extension of the Polish ‘bomba’ machines, from which their name was taken. The British bombe was quite a different thing.
In one sense, it was a philosophical response to the nature of Enigma. Despite the daunting number of combinations thrown up by Enigma, it none the less worked via a mechanical process. Thus, reasoned Turing, Enigma could also be thwarted mechanically. If Enigma, with its rotors, and wiring, and steckerboard, could encrypt, then surely an electric system involving circuits could decrypt.
As many veterans have pointed out, this wasn’t an entirely mechanical affair. For a bombe to work, it would require the push-start of a crib; that is, a series of words or a phrase, guessed at by hand and offered to the machine – which would then run through all the different letters and combinations to see if the crib would unravel the encoded text. In other words, such a machine would still require the initial power of human lateral thought. Nevertheless, in an era in which electronic telephone exchanges and television signals were brand new science, the notion of a machine that could take on the exhausting task of checking endless combinations at a speed beyond even an army of codebreakers was revolutionary.
When the young mathematician Oliver Lawn was recruited to Bletchley Park by Gordon Welchman, he found himself being diverted into the business of creating a bombe that would be effective. Construction took place in Letchworth, where Lawn oversaw this delicate and confidential work. In a technological sense, it was almost like being present at the construction of the first nuclear device. Certainly the impact that Turing’s codebreaking machine would have on the course of the war was immeasurably as profound.
‘Turing was a theoretician, Welchman was the practical chap,’ Mr Lawn says. ‘And the two put together their brainpower and evolved this machine which was made in large quantities in Letchworth by the British Tabulating Machine Company, as it was then called. In my early months, the first machines were being made.
‘I and several others used to go over and stay in a hotel in Baldock near Letchworth and work with the engineers on the making of the machine. The engineers had their engineering skill, we had none of that, but we had the mathematical skill. And we worked with the engineers – the chief engineer was Harold Keen, known familiarly as “Doc” Keen because he used to carry what looked like a doctor’s bag in his hand. He was a very bright engineer.
‘Because the Germans had devised new ways of encrypting, we had to find new methods to break the codes,’ he adds. ‘Eventually we got on to using cribs, guessing bits of messages, and testing them on the bombe machines which Turing and Welchman together had conceived. Then when the design of the machine was more or less settled, ‘they got on with it and more were produced. We weren’t needed after.’
The first bombe was called ‘Victory’. Given the months of painstaking work that had gone into its creation – and the acute sensitivity of the job that it was required to do – there was some debate on how the machine should be physically transported with maximum safety, and secrecy, from Letchworth to Bletchley.
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