Never-before-seen images shed light on world’s first digital computer


Colossus, a British codebreaking machine that helped defeat the Nazis, is celebrating its 80th anniversary.

A series of unseen images released earlier this week by GCHQ, the UK’s cyberintelligence agency, have put a new spotlight on the pivotal role Colossus played in World War Two and beyond.

The machine was developed during the war to decipher critical strategic messages between the most senior German generals in occupied Europe, but was so effective that it was used until the early 1960s and remained a secret for the rest of the century. Its existence was only confirmed in the early 2000s.

Considered to be the world’s first digital computer, Colossus decoded German messages that showed Allies had successfully managed to deceive Hitler into believing they were planning a land invasion from the coast of Calais in France rather than Normandy.

The Normandy landings, also known as D-Day, constituted the largest seaborne operation in history and was the turning point in the war. Historians credit Colossus and other codebreaking machines with playing a crucial role in shortening the war and saving millions of lives.

GCHQ said it was releasing the images to shed new light on the genesis and workings of Colossus, a room-sized mass of cables, tapes, and 2,500 valves. Standing at more than two meters tall, it deciphered messages in hours rather than weeks.

Newly-published photographs include a letter from 1943 that mentions engineer Tommy Flowers as having “produced a suggestion for an entirely different machine,” an idea that ultimately resulted in him designing and building Colossus.

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Part of letter discussing Colossus. Crown Copyright

Another part of the letter notes “rather alarming German instructions” Colossus was intercepting. Other images show Women’s Royal Naval Service members working on the computer and a blueprint of the computer.

Anne Keast-Butler, director of GCHQ, lauded the “creativity, ingenuity and dedication” behind Colossus that was as crucial for national security decades ago as it is now.

“Technological innovation has always been at the center of our work here at GCHQ, and Colossus is a perfect example of how our staff keep us at the forefront of new technology – even when we can’t talk about it,” Keast-Butler said.

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Work taking place on Colossus. Crown Copyright

Shrouded in secrecy

The first Colossus computer was delivered to Bletchley Park on January 18th, 1944. The site in South East England was the center of the Allied code breaking efforts during World War Two.

“The development of the Colossus machine was a huge advancement in Bletchley Park’s codebreaking efforts,” said Ian Standen, chief executive at Bletchley Park, which today serves as the museum.

By the end of the war, ten Colossus machines were operational and helped 550 people working on them to decipher 63 million characters of high-grade German communications.

Many of the experts who built the computer had no idea what they were assembling. Afterwards, only a small group, all sworn to the Official Secrets Act, knew about the true purpose of the machine.

Once the war ended, eight of the ten machines were destroyed and Flowers, the computer’s designer, was ordered to hand over all the documentation about it to GCHQ. Colossus remained shrouded in secrecy.

Bill Marshall, former GCHQ engineer, worked on Colossus for a year during the 1960s but said he had no idea what it was for.

“I was told very little about the machine I was working on – what the machine was actually doing was not for me to know. My job was to repair it as necessary, using just a few circuit diagrams and no detailed user handbook,” Marshall said.

Still, he said he was “very proud to have been involved with Colossus even in just a small way,” and that “we should all be proud of what was achieved in the name of national safety and security.”

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Blueprint of Colossus. Crown Copyright

Digital computing pioneer

As Colossus was kept secret for so long, its contribution to modern computing was not fully acknowledged until much later. According to the National Museum of Computing, which is based on Bletchley Park, it was the first electronic digital computer that could be programmed.

“Colossus was perhaps the most important of the wartime code breaking machines because it enabled the Allies to read strategic messages passing between the main German headquarters across Europe,” said Andrew Herbert, chairman of trustees at the National Museum of Computing.

According to Herbert, Colossus was an “important precursor” to modern computers even though its existence was not formally acknowledged until the digital age was well under way.

“Many of those who used Colossus at Bletchley Park went on to become important pioneers and leaders of British computing in the decades following the war, often leading the world in their work,” Herbert said.

In 2008, a functioning reconstruction of Colossus was built and is on display at the museum at Bletchley Park, alongside a copy of Alan Turing’s earlier “bombe” machine that decoded the German Enigma code.