Tommy Flowers

 

Inventor of Colossus, the vast valve computer that cracked the code of Hitler's messages to his generals

 

Reprinted from today's

TOMMY FLOWERS, who has died aged 92, built Colossus, the world's first programmable electronic computer, to help to crack Nazi Germany's most sophisticated cyphers.

The success of the Government Code and Cypher School at Bletchley Park in breaking the Enigma code is well known. Flowers was involved in a perhaps even more remarkable achievement -- the breaking of the encyphered teleprinter communications used by Hitler to talk to his generals.

These encyphered transmissions, known at Bletchley as Fish, were even more difficult to break, and the codebreakers attempted to use a basic computing machine known as Heath Robinson to assist in the process. Heath Robinson was a mechanical computer based on the ideas of Alan Turing the brilliant Cambridge mathematician who played a crucial role in the breaking of Enigma.

But it had a series of teething problems and, in early 1943, Turing, who was aware of Flowers's work with telephone systems for the Post Office, at Dollis Hill, suggested that he be called in.

Flowers swiftly realised that the problems with Heath Robinson could never he solved, and he made the radical proposal that the mechanical switching units, which made up the bulk of the computer, should be replaced by valves.

Flowers recalled later that his suggestion was met with disbelief on the part of the codebreakers who were convinced that valves were unreliable and would keep breaking down. Flowers, though, knew from his earlier work with the Post Office that if they were never moved or switched off valves would run and run.

He succeeded in persuading the codebreakers that valves would work, but then ran into a second problem. They asked him how long it would take to produce his machine. When he told them it could be done in a year, they replied that this was no good, since by then Hitler would have won.

The codebreakers decided that they would have to continue with Heath Robinson despite its drawbacks. But Flowers was by now so convinced that his valvebuilt machine would work that he decided to build it anyway. He and his team at Dollis Hill constructed the first prototype in 10 months, working around the clock. Colossus, as it was to become known, was demonstrated at Bletchley Park on December 8 1943.

The computer, designed to run through the many millions of possible settings for the code wheels on the German encyphered teleprinter system, was capable of processing 5,000 characters a second. But it was its accuracy in comparison with Heath Robinson that astounded the codebreakers.

They set out to test it by setting up a problem to which they already knew the answer. Each run took about half an hour, and they let Colossus run for four hours. It solved the problem eight times, on each occasion coming up with exactly the same answer.

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It was at once clear that Flowers's machine would be of inestimable assistance in helping the codebreakers to read communications between Berlin and all the German fronts. Perhaps more importantly, it was the first practical application of a large-scale programme-controlled computer, and as such the forerunner of post-war digital computers.

Thomas Harold Flowers was born in London on December 22 1905. After a four-year apprenticeship in mechanical engineering at the Woolwich Arsenal, he put himself through night school and earned a degree in engineering from London University.

By day, he worked at the GPO's research station at Dollis Hill. It was here that he began experiments with early electronic systems that would form the basis not only for Colossus. but also for advanced long-distance telephone systems that developed into modern direct dialling.

Following the success of Colossus Mark I. the Bletchley Park codebreakers asked Flowers to build an even bigger version, with 2,500 valves rather than the 1,500 employed in the prototype.

Flowers recalled that they told him the new Colossus had to be ready by June 1944 or it would not be of any use. Although the reasons for the deadline were never disclosed, he immediately realised its significance and Colossus Mark II was in place at Bletchley Park on June 1, five days before D-Day.

Colossus was constantly updated: by the end of the war there were 10 in operation, manned 24 hours a day by Wrens working to the programmes laid down by the codebreakers.

At the end of the war, all but two of the Colossi[*] were destroyed. Flowers was ordered to destroy all evidence that they had ever existed. The two surviving machines were taken first to Eastcote, west London, the first home of the new Government Communications Headquarters, and then to its present base at Cheltenham, where a Colossus was still operational in the early 1960s.

Flowers, who returned to the Post Office to continue his work on electronic telephone systems, received a £1,000 award for his war work, barely sufficient to pay off the debts that he had run up while developing Colossus. He was also appointed MBE. But his role in the breaking of the Nazi codes and the development of the modern computer remained a secret, even to his family, for many years.

Flowers received an honorary doctorate from Newcastle University in 1977, and another from Dc Montfort University in Leicester.

Tommy Flowers is survived by his wife, Eileen, and their two sons.

* Although The Daily Telegraph uses the plural Colossi, we think the word Colossus is 4th Declension: plural Colossus (long u). This Website would be glad to hear from Latin experts.