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Despite the British starting to crack the Enigma code, Germany had another trick up its sleeve: the Lorenz machine. More complex than the Enigma, the 12-rotor Lorenz was used exclusively for the most important messages between central high command in Berlin and German army field marshals.
It was rather larger than the Enigma and, as a result, not portable. It used the so-called "International Teleprinter Code", with each letter represented by five electrical impulses. Messages were encoded by adding a series of apparently randomly generated letters to the original plain text.
Max Newman, another Cambridge graduate, was assigned the task of building machines to break the Lorenz code.