The forgotten father of Colossus

Tom Flowers, head of switching research at the Post Office’s laboratory at London’s Dollis Hill, had almost missed the war. He was in Berlin on business in 1939 and got out with only hours to spare before the war started.

The Post Office in those days also ran the phone system, and Bletchley soon called on its switching expertise. Flowers helped build many of the early code-breaking machines, and he evidently impressed Turing.

Flowers did not think much of the latest machine, because he knew a better and very much faster way to do the task. More by luck than judgement, Bletchley had hired itself one of only a handful of people in the world familiar with digital electronics based on thermionic valves.

Turing was in America and the idea that the deciphering be done electronically came entirely from Flowers. He was not suggesting the construction of a computer, and probably barely knew the meaning of the word as we know it. He was an engineer addressing the specific problem of implementing the codebreakers’ logic in hardware.

In retrospect, it is clear that this was a historic moment: Turing and Flowers personify the marriage of mathematics and electronics that gave birth to computing. But no-one understood that at the time.
Flowers’ suggestion was met with incredulity at Bletchley Park, according to historian Jack Copeland.* But if his ideas had been better known, the Germans might have realised that its ciphers could be broken.

When Flowers said he would need a year to build his machine, Bletchley turned him down flat. Incredibly, he built it anyway, on his own initiative. His boss at Dollis Hill backed him and they put fifty people on the task.

At the end of 1943, he delivered a prototype to Bletchley where it caused a sensation. Flowers believed that the codebreakers had not really understood what he was doing. He recalled: “When the first machine was constructed and working, they just could not believe it.”

The machine, dubbed Colossus, immediately doubled the codebreakers’ output. By April, 1944, 12 more were on order. Flowers and Turing had between them helped shorten the war and launched the computer age. Neither would get a just reward and, as I’ll report in a later article, Flowers was written out of history for nearly half a century.

*Colossus: The Secrets of Bletchley Park’s Codebreaking Computers. Jack Copeland and others. ISBN 0-19-284055-X OUP £18.99

See part two of this series here.

See part three of three articles on early computing here.