Designed Colossus, the world’s first large-scale electronic computer

Transformed code-breaking, providing a better, faster way to break a code more complex than Enigma

Not afraid to simplify to solve complex issues

As much a father of computing as Alan Turing

Born in the East End of London in 1905, the son of a bricklayer, Tommy Flowers won a scholarship to technical college, became a mechanical apprentice at the Royal Arsenal in Woolwich and studied for his degree in engineering at evening classes.

In 1926 he went to work for the Post Office at its research centre in Dollis Hill, where he explored the use of electronics for telephone exchanges and became convinced that all-electronic systems were possible.

At Bletchley Park

He was first approached by Bletchley Park to work on the design of equipment for Enigma, but was later given the job of debugging the rather temperamental machine nicknamed Heath Robinson. Used to crack the Tunny code, it was a re-engineering of the German Lorenz SZ42 cipher machine which no-one on the Allied side actually saw until after the war had ended.

Tunny messages were sent in binary code—packets of zeroes and ones resembling the binary code used inside present-day computers. Decoding Tunny was vastly more difficult than the better known Enigma transmissions; Tunny used 12 cogs to Enigma’s four and was used only by the most senior German generals – and by Hitler himself.

Lorenz cipher machine

Overcoming scepticism

Flowers was convinced that he could build a better, faster all-electronic machine and planned an information processor with 2,000 electronic valves – then considered a preposterously colossal number – and a clock pulse to time and synchronise the processing steps.

Flowers’ ground-breaking proposal was met with scepticism. Electronic valves were thought to be too unreliable to use in such large numbers. However, before the war, Flowers had constructed installations containing more than 3,000 valves and knew that a valve left on all the time and not switched on and off would have a very long life.

Due to this lack of interest Flowers had to work on the project at Dollis Hill, with the support of the Chief Engineer and using his own money. Once he had started, the Bletchley Park management quickly realised their error and allocated a small team.

Simpler, quicker, better

One of Heath Robinson’s main issues was the problem of synchronising two input tapes. Ingeniously, Flowers simplified by doing away with one tape altogether. Colossus’s single paper tape contained the message to be cracked, while the crucial key data contained on Heath Robinson’s second tape was generated electronically by the computer’s circuits.

Flowers said that the Bletchley Park code breakers could hardly believe their eyes when they saw Colossus for the first time. It deciphered its first code on 5 January 1944. Flowers calmly noted in his diary: ‘Colossus did its first job today. Car broke down on way home.’

Operating at 5,000 characters per second, Colossus was analysing more than 100 messages a week, but Flowers knew he could do better. Employing parallel processing in the Mark II Colossus increased its speed to an astounding 25,000 characters per second – just in time to provide crucial intelligence for the D-Day invasion. Historians believe that cracking the Tunny code shortened the war by two years and that Colossus may still have been in use in the Cold War until around 1959 or 1960.

Colossus reconstruction at Bletchley Park

The world’s first computing centre

There were nine Colossi at Bletchley Park the by the end of the war, housed in two vast steel-framed buildings. It was the world’s first electronic computing facility, with job queues, teams of operators working round the clock in shifts, specialised tape-punching crews and engineers always on hand to keep the machinery running. Nothing like it was seen again until the 1960s, when the first large modern computing centres began to emerge.

The man who made Ernie

Tommy Flowers was awarded the MBE in 1943, along with a £1,000 grant – less than he had personally invested in the development of Colossus. After the war, he returned to the GPO to work on electronic switching systems; he also designed Ernie, the premium bond computer. For the rest of his career, Flowers was frustrated in his desire to make innovations. His design of Colossus would have lent weight to his ideas, but remained top secret. He watched sadly as the American computing industry outstripped Britain’s. Colossus was not publicly acknowledged until the 1970s. Flowers died in London in 1998.

You can read more about Tommy Flowers in Colossus: The Secrets of Bletchley Park’s Codebreaking Computers or visit Bletchley Park to see the reconstruction for yourself.