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Authors: Hervie Haufler
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in the security of their machine. The Germans could have made the use of cribs far more difficult if not impossible. All they needed to do was to add random bits of nonsense into their message beginnings and/or endings, or to insert Xs into long words, or to translate officers' titles into coded referencesâany such steps would have prevented accurate cribs from being applied. But they remained punctilious about spelling out honorifics and titles, and they continued to use repetitive phrases without any masking.
Turing's bombe, possessing the power of at least twelve Polish bombes, was designed to run an automatic test to determine whether a specific crib was contained in the message. He, however, had a limited view of what could be obtained even when his bombe succeeded. Essentially, he meant to look for the same sorts of closed letter loops that had been at the center of the Poles' technology. Turing's loops, however, had the great advantage of being drawn from cribs within the message rather than from its indicator. His bombe used the loops to detect incorrect positions and, by rejecting them, to arrive at the correct settings.
When it was built, though, this first bombe did not work well. To seek out merely small strings of letters did not produce enough rejections. There were many "Stops" that were found to be false only by hand testing. It was a slow and uncertain process.
Then Turing showed his plans to Welchman. In a flash of inspiration, Welchman saw that they didn't have to settle for closed loops. "By interconnecting the scramblers in a completely new way," he wrote in his memoir, The Hut Six Story, "one could increase the effectiveness of the automatic test by a very large number."
His new method involved adding to Turing's bombe the circuitry of what Welchman called a "diagonal board"âa matrix of terminals in a square in which the twenty-six letters of the alphabet were arranged horizontally, with another twenty-six vertically. His scheme capitalized on the reciprocal nature of the Enigma's plugboard connections. That is, if A is connected with Z and becomes Z in the encipherment, then the reverse is also true: Zbecomes A. His change ruled out false stops that the plugboards could make in Turing's bombe. The insertion of the diagonal board, as Welchman described it, "greatly reduced the number of runs that would be needed to insure success in breaking an Enigma key by means of a crib."
Turing, Welchman wrote, was incredulous at first, "but when he had studied my diagram he agreed that the idea would work, and became as excited about it as I was."
Turing's earlier design had guided the British Tabulating Machine Company in producing the first BP bombe. Now an improved design incorporating Welchman's diagonal board was put into production. The conversion benefited from Turing's mechanical bent. To do their required switching jobs, the bombes needed fast-working electrical relays. Turing drew from his electric multiplier to suggest designs for the bombes.
Patricia Bing, a teletypist who worked for Turing, later recalled how fellow workers at BP quickly adjusted to the unconventional ways of the man they began referring to as "the Prof." They understood that Turing thought little of his appearance or the impression he made. His clothes were a mess; his chewed-up fingernails most often had crescents of dirt beneath them; he could show up at BP entirely unaware that he was wearing two odd shoes. To control his allergies in pollen season he donned a gas mask when riding his bike. The bike had a bad habit of periodically throwing its chain; instead of taking the time to fix it he would count off the number of revolutions and stop just in time to make an adjustment. Bing remembered seeing Turing arrive on his bike and then "scuttle past us giggling girls, eyes downcast, as though in fear he might have to speak to one of us before he disappeared into his office." The papers he wrote and the designs he
Turing's bombe, possessing the power of at least twelve Polish bombes, was designed to run an automatic test to determine whether a specific crib was contained in the message. He, however, had a limited view of what could be obtained even when his bombe succeeded. Essentially, he meant to look for the same sorts of closed letter loops that had been at the center of the Poles' technology. Turing's loops, however, had the great advantage of being drawn from cribs within the message rather than from its indicator. His bombe used the loops to detect incorrect positions and, by rejecting them, to arrive at the correct settings.
When it was built, though, this first bombe did not work well. To seek out merely small strings of letters did not produce enough rejections. There were many "Stops" that were found to be false only by hand testing. It was a slow and uncertain process.
Then Turing showed his plans to Welchman. In a flash of inspiration, Welchman saw that they didn't have to settle for closed loops. "By interconnecting the scramblers in a completely new way," he wrote in his memoir, The Hut Six Story, "one could increase the effectiveness of the automatic test by a very large number."
His new method involved adding to Turing's bombe the circuitry of what Welchman called a "diagonal board"âa matrix of terminals in a square in which the twenty-six letters of the alphabet were arranged horizontally, with another twenty-six vertically. His scheme capitalized on the reciprocal nature of the Enigma's plugboard connections. That is, if A is connected with Z and becomes Z in the encipherment, then the reverse is also true: Zbecomes A. His change ruled out false stops that the plugboards could make in Turing's bombe. The insertion of the diagonal board, as Welchman described it, "greatly reduced the number of runs that would be needed to insure success in breaking an Enigma key by means of a crib."
Turing, Welchman wrote, was incredulous at first, "but when he had studied my diagram he agreed that the idea would work, and became as excited about it as I was."
Turing's earlier design had guided the British Tabulating Machine Company in producing the first BP bombe. Now an improved design incorporating Welchman's diagonal board was put into production. The conversion benefited from Turing's mechanical bent. To do their required switching jobs, the bombes needed fast-working electrical relays. Turing drew from his electric multiplier to suggest designs for the bombes.
Patricia Bing, a teletypist who worked for Turing, later recalled how fellow workers at BP quickly adjusted to the unconventional ways of the man they began referring to as "the Prof." They understood that Turing thought little of his appearance or the impression he made. His clothes were a mess; his chewed-up fingernails most often had crescents of dirt beneath them; he could show up at BP entirely unaware that he was wearing two odd shoes. To control his allergies in pollen season he donned a gas mask when riding his bike. The bike had a bad habit of periodically throwing its chain; instead of taking the time to fix it he would count off the number of revolutions and stop just in time to make an adjustment. Bing remembered seeing Turing arrive on his bike and then "scuttle past us giggling girls, eyes downcast, as though in fear he might have to speak to one of us before he disappeared into his office." The papers he wrote and the designs he
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