Bletchley Park Tour

Tommy Flowers, MBE (1905-1998)

For intelligence at the highest level, the codebreakers needed to crack 'Tunny', the teleprinter code used by Hitler and his generals. Tunny posed a formidable challenge. Transmitted on a 12-rotor machine called Lorenz, it was several orders of magnitude more complex than Enigma. Again, the odds were heavily stacked against the codebreakers. The involvement of Tommy Flowers, a bright young telephone engineer, was to be crucial in overcoming those odds.

Decyphering Tunny by hand took far too long for the intelligence to be of use. The answer lay in automating the process. The first attempt, 'Heath Robinson', was a partial success but was slow and unreliable. Alan Turing recommended enlisting the help of Flowers, who had first come to his attention during work on the Bombe.

Flowers, an engineering graduate, was involved in experiments with electronic telephone transmissions at Dollis Hill, the research arm of the Post Office (which at that time oversaw the nation's communications).

Flowers asserted that the problems inherent in Heath Robinson could not be solved and that a radical shift in design philosophy was required. His Dollis Hill experiments would form the basis of Heath Robinson's successor. Flowers proposed to replace Robinson's mechanical switching units with valves. Hundreds and hundreds of valves. His proposal met with widespread scepticism. Flowers later recalled:

"They wouldn't believe it. They were quite convinced that valves were very unreliable. This was based on their experience of radio equipment which was carted around, dumped around, switched on and off, and generally mishandled. But I'd introduced valves into telephone equipment in large numbers before the war and I knew that if you never moved them and never switched them off they would go on forever."

After convincing the codebreakers of his valve theory, Flowers's next battle was against the clock. When he estimated that his machine could be built in a year, the codebreakers replied that this was not good enough, fearing that Hitler would have won by then. The codebreakers saw no option but to persevere with Heath Robinson.

But by now, Flowers was so convinced that his valve-built machine would work that he built it anyway. Working around the clock, he and his team at Dollis Hill constructed the first prototype in 10 months, demonstrating it at Bletchley Park on 8th December 1943. 'Colossus', as it was to become known, did the same job as Heath Robinson but much faster and more reliably.

The size of a small room and weighing one ton, Colossus was put together partly with standard telephone exchange parts. Flowers described his invention as "a string and sealing wax affair". Nevertheless, it could do in hours what might otherwise have taken weeks. It was the world's first programmable electronic computer.

Following the success of Colossus I, ten Mark II models were built, powered by even more valves (2,500 instead of 1,500). Flowers was instructed that, to be of any use, the Mark II must be in place by June 1944. It was installed at Bletchley Park on 1st June. Its contribution, five days later, to the success of D-Day was enormous. The Ultra from Colossus provided the Allies with the complete German order of battle, and also enabled them to monitor German reaction to their deception tactics.

Awarded an MBE and £1,000 for his secret work, Flowers returned to the Post Office after the war. As head of the switching group at Dollis Hill he invented long-distance telephone systems which were the forerunner of modern direct dialling. He said nothing about his wartime activities for many years, not even to his family. It was not until Bletchley Park began to give up its secrets in the 1970s that Flowers's role was revealed.

His life's work was acknowledged by the award of the Post Office's first Martlesham Medal in 1980. Along with Alan Turing and Max Newman, Tommy Flowers is now widely credited as one of the fathers of the modern computer.

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