Computing with Quantum Cats by John Gribbin Read Free Book Online

reliable (sometimes it would give different results if set the same problem twice). But it proved that the machine approach to breaking Tunny could work. What was needed was a better machine, and by great good fortune the man Bletchley Park asked to build a better machine was exactly the right man for the job.
    Among those who had worked on the construction of Heath Robinson were engineers at the Post Office research station in Dollis Hill in north London, who knew all about relays from their work on automatic telephone exchanges. The top engineer at Dollis Hill was Thomas Flowers (known as “Tommy” at the time, although he preferred “Tom” in later life). Born in London's East End in 1905, Flowers was the son of a bricklayer, and a genuine Cockney. He had won a scholarship to a technical college, and then joined the Post Office as a trainee telephone engineer, continuing his studies at evening classes and earning a post at Dollis Hill in 1930. There, he pioneered the use of electronic valves for switching in the 1930s, flying in the face of the received wisdom that such valves were unreliable and prone to break down. He hadfound that the problems arose when valves were repeatedly turned on and off, but that if they were left on all the time, glowing like little incandescent light bulbs, they would run reliably for a very long time without burning out. As early as 1934, he had worked on an experimental telephone switching system using four thousand valves, and a design based on his work had just started to come into operation at the beginning of the war. Flowers himself, though, very nearly spent the war interned in Germany. He was working in Berlin in the late summer of 1939, but fortunately was warned by the British Embassy to go home, and crossed the border into Holland a few hours before the frontier was closed.
    Flowers was asked to help with Heath Robinson because Turing had discussed with him the possibility of building an electronic version of the Bombe; although this never happened, Turing was impressed by the engineer and recommended him to Newman as the right man to fix the problems with Heath Robinson. But when he was asked for his advice on how to make the relays in Heath Robinson more reliable, Flowers’ reply was that the best thing to do would be to forget about mechanical relays altogether, and use valves instead.
    The idea of a reliable machine using a couple thousand electronic valves was regarded as a fantasy by Newman and his colleagues, who doubted that even if it could be built it would be working in time to contribute to the war effort (this was in February 1943). Flowers was told that he was welcome to try once he was back at Dollis Hill, and in the meantime, rather than officially encouraging the project, Newman ordered another dozen Heath Robinson type machines. But the Director of the Dollis Hill research station, W. G. Radley, saw the potential of the idea (and had first-hand knowledge ofFlowers’ success with valve-based machines) and gave his full support to the enterprise (moral support, that is: funds were limited, and Flowers had to pay for some of the equipment himself). The result was a prototype machine, dubbed Colossus, which used 1,600 valves and required only one paper tape, carrying the message to be broken, as the “chi-stream” to be tested—all the possible settings of the chi-wheels—was generated electronically. After a heroic round-the-clock effort by Flowers and his colleagues, Colossus was tested at Dollis Hill in December 1943, then disassembled and taken on trucks to Bletchley Park, where it arrived on January 18, 1944. Re-assembled, it filled a whole room. The Bletchley Park codebreakers, including Newman, were astonished: “I don't think they [had] really understood what I was saying in detail—I am sure they didn't—because when the first machine was constructed and working, they obviously were taken aback. They just