Tommy Flowers

Thomas Harold Flowers MBE (22 December 1905 - 28 October 1998) was an English engineer with the British General Post Office.

During World War II, Flowers designed and built Colossus, the world's first programmable electronic computer, to help decipher encrypted German messages.

Flowers was born at 160 Abbott Road, Poplar in East London on 22 December 1905, the son of a bricklayer.

Whilst undertaking an apprenticeship in mechanical engineering at the Royal Arsenal, Woolwich, he took evening classes at the University of London to earn a degree in electrical engineering.

In 1926, he joined the telecommunications branch of the General Post Office (GPO), moving to the Post Office Research Station at Dollis Hill in Middlesex in 1930.

From 1934 onward, he explored the use of electronics in telephone exchanges.

In 1935, Flowers and Eileen Margaret Green were married.

The couple later had two children, John and Kenneth.

By 1939, his design of equipment using 3000 to 4000 valves was in limited operation for (say) 1000 lines at an exchange with each line having three or four valves.

Note that this was for (amplified) long distance or trunk lines between exchanges (central offices), using in-band signalling with switching at each end carried out by electromechanical switches or operators.

As Flowers remarked, at the outbreak of war “he was possibly the only person in Britain who realised that valves could be used reliably on a large scale for high-speed computing.

He was convinced that an all-electronic system was possible.

A background in switching electronics would prove crucial for his computer designs.

Flowers had first met (and got on with) Turing in 1939 but was treated with disdain by Gordon Welchman, because of his advocacy of valves rather than relays.

Welchman preferred the views of Wynn-Williams and Keene of the British Tabulating Machine Company (BTM) who had designed and constructed the Bombe and wanted Radley and "Mr Flowers of Dollis Hill" removed from work on Colossus for "squandering good valves".

Despite the success of Colossus, the Heath Robinson approach was still valuable for solving certain problems.

The final development of the concept was a machine called Super Robinson that was designed by Tommy Flowers.

This one could run four tapes and was used for running depths and "cribs" or known-plaintext attack runs.

Flowers' first contact with wartime codebreaking came in February 1941 when his director, W. Gordon Radley, was asked for help by Alan Turing, who was working at Bletchley Park, the government codebreaking establishment, 50 mi north west of London in Buckinghamshire.

Turing wanted Flowers to build a counter for the relay-based Bombe machine, which Turing had developed to help decrypt German Enigma codes.

The "Counter" project was abandoned but 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 code generated by a teletypewriter in-line cipher machine, the Lorenz SZ40/42, one of their Geheimschreiber (secret writer) systems, called "Tunny" (tuna fish) 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, in an attempt to automate the cryptanalysis of the Lorenz SZ-40/42 cipher machine.

Flowers proposed a more sophisticated alternative, using an electronic system, which his staff called Colossus, using perhaps 1,800 thermionic valves (vacuum tubes) instead of 150 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 management were not convinced and merely encouraged Flowers to proceed on his own.

He did so at the Post Office Research Labs, using some of his own funds to build it.

On 2 June 1943, Flowers was made a member of the Order of the British Empire.

Flowers gained full backing for his project from the director of the Post Office Research Station at Dollis Hill, W. G. Radley.

With the highest priority for acquisition of parts, Flowers's team at Dollis Hill built the first machine in eleven 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, named Heath Robinson, which used electro-mechanical switches.

The first Mark 1, with 1500 valves, ran at Dollis Hill in November 1943; it was delivered to Bletchley Park in January 1944 where it was assembled and began operation in early February.

The algorithms used by Colossus were developed by W. T. Tutte and his team of mathematicians.

Colossus proved to be efficient and quick against the twelve-rotor Lorenz cipher SZ42 machine.

In anticipation of a need for additional computers, Flowers was already working on Colossus Mark 2 which would employ 2,400 valves.

The first Mark 2 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 summarising a Colossus decrypt.