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Holiday 2014 / 2015 Tempus-Magazine.com 74 and discreetly bought it. Te code breakers were located in the cot- tages, stables, and some prefab- ricated huts that were erected on the grounds. Turing was assigned to a team working in Hut 8 that was trying to break the German Enigma code, which was generated by a portable machine with mechanical rotors and electrical circuits. It encrypted military messages by using a ci- pher that, after every keystroke, changed the formula for substitut- ing letters. Tat made it so tough to decipher that the British despaired of ever doing so. A break came when Polish intelligence ofcers created a machine based on a captured German coder that was able to crack some of the Enigma codes. By the time the Poles showed the British their machine, however, it had been rendered ineffective because the Germans had added two more rotors and two more plug- board connections to their Enigma machines. Turing and his team went to work creating a more so- phisticated machine, dubbed "the bombe," that could decipher the improved Enigma messages—in particu- lar, naval orders that would reveal the deployment of U-boats that were decimating British supply convoys. Te bombe exploited a variety of subtle weaknesses in the coding, including the fact that no letter could be enciphered as itself and that there were certain phrases the Germans used repeatedly. By August 1940 Turing's team had two operating bombes, which were able to break 178 coded messages; by the end of the war they had built close to two hundred. Te Turing-designed bombe was not a notable advance in computer technology. It was an electrome- chanical device with relay switch- es and rotors rather than vacuum tubes and electronic circuits. But a subsequent machine produced at Bletchley Park, and Colossus, was a major milestone. Te need for Colossus arose when the Germans started coding impor- tant messages, such as orders from Hitler and his high command, with an electronic digital machine that used a binary system and twelve code wheels of unequal size. Te electromechanical bombes de- signed by Turing were powerless to break it. It required an attack using lightning-quick electronic circuits. Te team in charge, based in Hut 11, was known as the Newmanry after its leader, Max Newman, the Cambridge math don who had in- troduced Turing to Hilbert's prob- lems almost a decade earlier. New- man's engineering partner was the electronics wizard Tommy Flow- ers, a pioneer of vacuum tubes, who worked at the Post Ofce Re- search Station at Dollis Hill, a London suburb. Turing was not part of Newman's team, but he did come up with a statistical approach, dubbed "Turingery," that detected any departures from a uniform distribution of characters in a stream of ciphered text. A machine was built that could scan two loops of punched paper tapes, using photoelectric heads, in order to compare all possible permutations of the two sequences. Te machine was dubbed the "Heath Robinson," after a British cartoonist who specialized, as did Rube Goldberg in America, in drawing absurdly complex mechanical contraptions. For almost a decade Flowers had been fascinated by electronic circuits made with vacuum tubes, which he and other Brits called "valves." As an engineer with the Post Ofce's telephone division, he had created in Walter Isaacson is the president and CEO of the Aspen Institute, a nonpartisan educational and policy studies institute based in Washington, DC. He has been the chairman and CEO of CNN and the editor of TIME magazine. Isaacson's latest book, The Inno- vators: How a Group of Inventors, Hackers, Geniuses, and Geeks Created the Digital Revolution is a biographical tale of the people who invented the computer, Inter- net and the other great innova- ABOUT T H E A U T H O R tions of our time. He is the author of Steve Jobs (2011), Einstein: His Life and Universe (2007), Benjamin Franklin: An American Life (2003), and Kissinger: A Biography (1992), and coauthor of The Wise Men: Six Friends and the World They Made (1986). Isaacson is a graduate of Har- vard College and of Pembroke College of Oxford University, where he was a Rhodes Scholar. He began his career at The Sunday Times of London and then the New Orleans Times- M A R K I Alan Turing reviews the Mark I computer built by Ferranti, a British weapons and electronics company. P H O T O B Y S S P L / G E T T Y I M A G E S