The rebuild of the Colossus computer at the National Museum of Computing

Code-breaking veterans celebrate Colossus' 70th birthday

The world's first electronic computer celebrates its 70th birthday today, with a ceremony attended by code-breaking veterans and their families.

The Colossus Mk I, designed to speed up code-breaking of the sophisticated Lorenz cipher used by Hitler and his generals during the Second World War, went on line seventy years ago today and is regarded as the world's first fully programmable, digital, electronic computer.

By the end of the war there were 10 functioning Colossi machines, which had a decisive impact on the Allied victory, and to mark the milestone Colossus veterans and their families will gather today at The National Museum of Computing at Bletchley Park to see a re-enactment of the code-breaking process from intercept to decrypt with a working rebuild of Colossus.

"The achievements of those who worked at Bletchley Park are humbling,” said Tim Reynolds, chair of the museum.

"The working Colossus rebuilt by the late Tony Sale (museum co-founder) and his team provides a mesmerising start to our story of the history of computing at The National Museum of Computing. It fascinates people of all ages and we see on a daily basis the inspiration that it provides to school groups who visit the Museum.

The code was first heard in 1940 in encrypted German teleprinter signals by British police officers on the south coast listening for possible spy transmissions, but it wasn’t until an error by a German operator in August 1941 that enabled top code-breaker Colonel John Tiltman to decipher a message, that mathematician Bill Tutte was able on to deduce the complete structure of the Lorenz machine.

Code-breakers in the Testery – the Bletchley Park section founded to break what the British cryptographers nicknamed the Tunny code – began cracking the messages by hand, but mathematician Max Newman started work to automate the system.

British engineer Tommy Flowers tried to improve his method, which used electro-mechanical Robinson machines, and instead designed Colossus, the world's first electronic computer, which worked by finding the start-wheel positions of Lorenz-encrypted messages.

Occupying the size of a living room, Colossus weighed five tonnes, used 8kW of power and incorporated 2,500 valves and 10,000 resistors connected by 4.3 miles of wiring. It enabled the start-wheel positions to be found in a few hours, shortening the code-breaking process and allowing larger numbers of messages to be broken.

Colossus Mark I, which began operating on February 5 1944, was succeeded in June that year by the Mark II. By the end of the war, 63 million characters of high-grade German messages had been decrypted by the 550 people working on the Colossi at Bletchley Park.

The messages provided the Allies with crucial intelligence on what enemy forces were planning, giving them decisive advantages – such as knowing that Hitler believed the D-Day landings in June 1944 would be at Calais rather than Normandy.

"Bill Tutte's ingenuity in deducing out how the Lorenz machine worked without ever having seen it, the skill of those in the Testery who broke the cipher by hand, and Tommy Flowers' design of the world's first electronic computer Colossus to speed up the code-breaking process are feats almost beyond comprehension,” said Reynolds.

"February 5 will be a proud day for the museum to host the Colossus and Tunny veterans who are able to make the journey today. This day is in honour of all the men and women who worked on breaking the Lorenz cipher."

The existence of Colossus was kept top secret for 30 years because of the sophistication and sensitivity around the encryption it had helped to break. Many of those who worked on it went on to build other computers and technology.

In honour of the men and women who worked at Bletchley Park during the Second World War, museum co-founder Tony Sale led a team to rebuild Colossus in 1994, using eight photographs of it taken in 1945 and a few circuit diagrams kept by engineers who worked on the original computer.

On November 15, 2007, a rebuilt fully-functioning Colossus Mark II was unveiled to the public at the National Museum of Computing, and in March 2012 the Colossus Rebuild was presented in a new extended gallery, allowing visitors to walk around the machine for the first time.

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