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had made in reconstructing the Wehrmacht ’s steckered Enigma machine.
    The Bureau Szyfrow had broken a number of German codes during the early 1920s but the introduction of Enigma had left them unable to read the Wehrmacht ’s messages. Their response was to recruit mathematics students and put them through a codebreaking course. Only three passed. Their names were Jerzy Różycki, Henryk Zygalski and Marian Rejewski. All three were recruited but worked initially on a part-time basis and it was only in September 1932 that Rejewski, the best of the three, was given the steckered Enigma machine and asked to solve it. By the end of that year, assisted by Enigma key lists obtained by the French from Asche , he had reconstructed the wiring mathematically, using permutation theory. By the beginning of 1938, assisted by the fact that the Germans were not changing the settings frequently, Rejewski and his colleagues were able to solve 75 per cent of the Poles’ intercepts of German Army Enigma messages. ‘We were decyphering every day and often at a record speed,’ he recalled.
    In the autumn of that year, they began using electro-mechanical machinery known as Bomby – literally ‘bombs’, a name that derived from the ticking noise they made. The Bomby were used to identify ‘females’, repetitive letters in the Enigma keys, to break the messages. But the introduction, in December, of two additional wheels, allowing further different permutations of wheel order, brought the Polish successes to a halt. Rejewski succeeded in reconstructing the wiring of the two new wheels but the Poles no longer had enough Bomby to run through the much greater number of possibilities the new wheels had created. They needed help and believed the British could provide it, said Colonel Stefan Mayer, the officer in charge of the Bureau Szyfrow . ‘As the danger of war becametangibly near we decided to share our achievements regarding Enigma, even not yet complete, with the French and British sides, in the hope that working in three groups would facilitate and accelerate the final conquest of Enigma.’
    The Poles explained how they used the Bomby and the Netzverfahren or ‘grid system’ invented by Zygalski. These were lettered sheets of paper with holes punched in them to help to break the keys and wheel orders by identifying the ‘females’. But the introduction of the fourth and fifth wheels had meant they had to use far more Bomby and sheets than they could possibly produce. Knox was furious to discover that the Poles had got there first, sitting in ‘stony silence’ as they described their progress and produced a clone of the Enigma machine, reconstructed using the knowledge they had built up over the previous six years. But his good humour soon returned after they told him that the keys were wired up to the encypherment mechanism in alphabetical order, A to A, B to B, etc. Although one female codebreaker had suggested this as a possibility, it had never been seriously considered, Twinn recalled. ‘It was such an obvious thing to do, really a silly thing to do, that nobody, not Dilly Knox or Tony Kendrick or Alan Turing, ever thought it worthwhile trying,’ he recalled. ‘I know in retrospect it looks daft. I can only say that’s how it struck all of us and none of the others were idiots.’
    A few weeks later the Poles gave both the French and British codebreakers clones of the steckered Enigma. Bertrand, who had been given both machines and asked to pass one on to the British, later described taking the British copy to London on the Golden Arrow express train on 16 August 1939. He stepped down from the train at Victoria station to find the deputy head of MI6 Colonel Stewart Menzies standing on the platform, swathed in smoke and wearing a dinner jacket on which was pinned the rosette of the Legion d’Honneur . Bertrand handed the machine over to Menzies with the words, ‘ Accueil Triompha l ’ – ‘a triumphant