Thomas "Tommy" Harold Flowers, MBE (1905 - 1998)

In 1926, Tommy Flowers joined the telecommunications branch of the General Post Office (GPO), moving

to work at the research station at Dollis Hill in North-West London in 1930. From 1935 onward, he explored

 the use of electronics for telephone exchanges. By 1939, he was convinced that an all-electronic system

was possible. This background in switching electronics would prove crucial for his computer design in

World War II.

 

Flowers's first contact with the wartime code breaking effort came in February 1941 when his Director was

asked for help by Alan Turing, who was then working at the government's Bletchley Park code breaking

establishment 50 miles north west of London. 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

cryptanalysis of the 'Lorenz' cipher. This was a high-level German cipher generated by a teletypewriter

cipher machine, 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 and Frank Morrell (also at Dollis Hill) designed the 'Heath Robinson', the first machine designed to decrypt the 'Lorenz' or 'Fish' machine cyphers.

 

Flowers proposed an electronic system, which he called 'Colossus', using perhaps 1,800 Thermionic valves (vacuum tubes), and having only one paper tape instead of two (which required synchronisation) by generating the wheel patterns electronically. Because the most complicated previous electronic device had used about 150 valves some were sceptical that the system 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 with 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.

 

Flowers gained full backing for his project from the Director of Dollis Hill. 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. The Mark 1 'Colossus' operated five times faster and was more flexible than the previous system, 'Heath Robinson', which used electro-mechanical switches. The first Mark 1, with 1500 valves, ran at Dollis Hill in November 1943, and then at Bletchley Park in January 1944.

 

A Mark 2 redesign utilizing 2,400 valves had begun before the first computer was finished, in anticipation of a need for additional computers. The first Mark 2 'Colossus' went 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 Marshal 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 2 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 code breaking operations of the Cold War".

 

They were finally decommissioned in 1959 and 1960.

 

After the war, Flowers was granted £1,000 by the government, payment which did not cover Flowers' personal investment in the equipment and most of which he shared amongst the staff who helped him build and test 'Colossus' . Ironically, Flowers applied for a loan from the Bank of England to build another machine like 'Colossus'  but was denied the loan because the bank did not believe that such a machine could work. He could not argue that he had already designed and built many of these machines because his work on 'Colossus'  was covered by the 'Official Secrets Act'. His work in computing was not fully acknowledged until the 1970's. His family had known only that he had done some 'secret and important' work. He remained at the Post Office Research Station where he was Head of the Switching Division. He and his group pioneered work on all-electronic telephone exchanges, completing a basic design by about 1950, which led on to the Highgate Wood Telephone Exchange. He was also involved in the development of 'ERNIE' the Random Number Generator that picked out Premium Bond numbers.

 

Tommy Flowers retired in 1969.

Photo: Unknown • Believed to be in the Public Domain

(Age - Copyright expired)