Colossus decrypts to be revealed after 75 years

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The 75th anniversary of the first attack by the Colossus computer on a Second World War enemy Lorenz message has coincided with the discovery of a selection of original decrypts showing the nature of the intelligence that was intercepted. The decrypts are now being analysed by researchers for a special display in the Colossus Gallery at The National Museum of Computing in May to mark the 75th anniversary of the arrival of Colossus Mk II in time for D-Day in 1944.

On 5 February 1944, Colossus Mk I attacked its first message encrypted by Lorenz, the highly sophisticated cipher used in communications between Hitler and his generals during the Second World War.

Designed by brilliant British telecommunications design engineer Tommy Flowers, Colossus was built to speed up code-breaking of the hugely complex Lorenz cipher. By the end of the war there were ten functioning Colossi and they made a decisive impact in shortening the war and saving countless lives.

News of the existence of the Colossus, widely regarded as the first electronic computer, was kept top secret for 30 years partly because of the sophistication of its methods to help break Lorenz messages by finding the frequently changing wheel patterns of the Lorenz encryption machine.

Standing 2m high, 5 m wide and almost 4 m deep (7 ft by 17 ft by 11 ft), Colossus weighed five tonnes, and used 8 kW of power. Colossus Mark II, which arrived at Bletchley Park in May 1944, had 2,500 valves and 7 km of wiring, and was able to read 5000 characters per second (faster than anything ever produced commercially).

By accelerating the discovery of the wheel patterns of the ever-changing Lorenz-encrypted messages, 63 million characters of high-grade German messages had been decrypted by 550 people working on the ten functioning Colossus machines at Bletchley Park by the end of the war.

The full impact of Colossus continues to be revealed. Although its existence was kept secret until 1975, many of those who worked on Colossus went on to build other computers and technologies, confident in the knowledge that it was possible to build reliable machines of such complexity using valves.

Andrew Herbert, chair of The National Museum of Computing, said, “The working rebuild of Colossus at The National Museum of Computing is an inspiration to all our visitors who are astonished when they see the working machine and learn of its impact.

“The achievements of those who worked at wartime Bletchley Park are humbling. Despite decades of secrecy, the names of the key characters involved with the breaking of Lorenz and the construction of Colossus are becoming increasingly well-known. Bill Tutte who deduced how the Lorenz machine worked, Major Tester and the Testery who broke the cipher by hand, and Tommy Flowers who designed Colossus to speed up the code-breaking process are just a few of the names that are familiar to many today, but who were largely unknown for decades after the war.

"At our museum today, the working Colossus rebuilt by the late Tony Sale and his team provides a mesmerising beginning to our story of the history of computing. It never fails to generate awe and spark the imagination of visitors of all ages.”

About The National Museum of Computing

The National Museum of Computing, located on Bletchley Park in Block H, one of England’s ‘irreplaceable places’, is an independent charity housing the world's largest collection of functional historic computers, including reconstructions of the wartime code-breaking Colossus and the Bombe, and the WITCH, the world's oldest working digital computer. The Museum enables visitors to follow the development of computing from the ultra-secret pioneering efforts of the 1940s through the large systems and mainframes of the 1950s, 60s and 70s, and the rise of personal computing in the 1980s and beyond.

The Museum runs a highly successful Learning Programme for schools and colleges and promotes introductions to computer coding amongst young people to inspire the next generation of computer scientists and engineers.

Sponsors of the Museum have included Bletchley Park Science and Innovation Centre, Fujitsu,, Paessler, Sophos, Lenovo, Bloomberg, Ocado Technology, Ceravision, CreateOnline, 4Links, Google UK, IBM, NPL, HP Labs, FUZE and BCS.

The whole Museum is open to the public from 12 noon - 5 pm on Thursdays, Saturdays and Sundays, spring and summer Bank Holidays. During long school holidays, there are additional opening days. The Colossus and Tunny galleries are open daily. Public and private Guided Tours are available and bookable online – see the website for details. Educational and corporate group visits are available by prior arrangement.

Please note: the First Generation Gallery and the Mainframes Gallery are currently closed because of a roof refurbishment. They are expected to be re-opened in March.

For more information, see and follow @tnmoc on Twitter and The National Museum of Computing on Facebook.

Media Contacts

Stephen Fleming, Palam Communications, for The National Museum of Computing
01635 299116

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