Tommy Flowers - World War II

World War II

Flowers's first contact with the wartime codebreaking effort came in February 1941 when his director, W Gordon Radley was asked for help by Alan Turing, who was then working at the government's Bletchley Park codebreaking establishment 50 miles north west of London in Buckinghamshire. Turing wanted Flowers to build a decoder for the relay-based Bombe machine, which Turing had developed to help decrypt the Germans' Enigma codes. Although the decoder project was abandoned, Turing was impressed with Flowers's work, and in February 1943 introduced him to Max Newman who was leading the effort to automate part of the work of Cryptanalysis of the Lorenz cipher. This was a high-level German cipher generated by a teletypewriter in-line cipher machine, the SZ40/42, one of their "Geheimschreiber" (secret writer) systems, that was called "Tunny" by the British. It was a much more complex system than Enigma; the decoding procedure involved trying so many possibilities that it was impractical to do by hand. Flowers proposed an electronic system, which he called Colossus, using over 1,800 thermionic valves (vacuum tubes). Because the most complicated previous electronic device had used about 150 valves, some were sceptical that such a device would be reliable. Flowers countered that the British telephone system used thousands of valves and was reliable because the electronics were operated in a stable environment that included having the circuitry on all the time. The Bletchley Park management were not convinced, however, and merely encouraged Flowers to proceed on his own. He did so, providing much of the funds for the project himself. On 2 June 1943, he was made a Member of the Order of the British Empire.

Flowers gained full backing for his project from the director of Dollis Hill, W. G. Radley. With the highest priority for acquisition of parts, Flowers's extremely dedicated team at Dollis Hill built the first machine in 11 months. It was immediately dubbed 'Colossus' by the Bletchley Park staff for its immense proportions. It operated five times faster and was more flexible than the previous system, named Heath Robinson, which used electro-mechanical switches. Anticipating the need for additional computers, a Mark 2 redesign utilizing 2,400 valves was begun before the first computer was finished.

The first Mark 2 Colossus was put into service at Bletchley Park on 1 June 1944, and immediately produced vital information for the imminent D-Day landings planned for Monday 5 June (postponed 24 hours by bad weather). Flowers later described a crucial meeting between Dwight D. Eisenhower and his staff on 5 June, during which a courier entered and handed Eisenhower a note summarizing a Colossus decrypt. This confirmed that Hitler wanted no additional troops moved to Normandy, as he was still convinced that the preparations for the Normandy Landings were a diversionary feint. Handing back the decrypt, Eisenhower announced to his staff, "We go tomorrow." Earlier, a report from Field Marshall Rommel on the western defences was decoded by Colossus and revealed that one of the sites chosen as the drop site for an US parachute division was the base for a German tank division. The site was changed.

Years later, Flowers described the design and construction of these computers. Ten Colossi were completed and used during World War II in British decoding efforts, and an eleventh was ready for commissioning at the end of the war. All but two were dismantled at the end of the war. "The remaining two were moved to a British Intelligence department, GCHQ in Cheltenham, Gloucestershire, where they may have played a significant part in the codebreaking operations of the Cold War". They were finally decommissioned in 1959 and 1960.