Colossus veterans and their families gather today at The National Museum of Computing located on Bletchley Park to celebrate the 70th anniversary of Colossus, the world's first electronic computer. They will see a re-enactment of the code-breaking process from intercept to decrypt with a working rebuild of Colossus.
On 5 February 1944 Colossus Mk I attacked its first Lorenz-encrypted message, the highly sophisticated cipher used in communications between Hitler and his generals during World War II.
Designed by brilliant British telephone engineer Tommy Flowers, Colossus was built to speed up code-breaking of the complex Lorenz cipher. By the end of the war there were ten functioning Colossi and they had a decisive impact in shortening the war and saving countless lives.
Colossus was the first electronic computer, but news of its existence was kept top secret for 30 years because of the sophistication and sensitivity surrounding the encryption it had helped to break.
The statistics of Colossus are astounding. It occupied the size of a living room (7 ft high by 17 ft wide and 11 ft deep), weighed five tonnes, and used 8kW of power. It incorporated 2,500 valves, 501 of which are thyraton switches, about 100 logic gates and 10,000 resistors connected by 7 km of wiring. Reading 5000 characters per second (faster than anything ever produced commercially), Colossus found the start wheel positions of Lorenz-encrypted messages to enable the decryption of 63 million characters.
Typically, it took Colossus up to four hours to establish the start wheel positions of messages. It is often surmised that the Allies might have been reading some of the decrypted messages even before they reached German High Command. By the end of the war, 63 million characters of high-grade German messages had been decrypted by the 550 people working on the ten functioning Colossi at Bletchley Park.
As the first electronic computer, the legacy of Colossus lives on. It had to be kept secret for 30 years, but many of those who worked on it went on to build other computers and technologies, using the knowledge that it was possible to build reliable machines of such complexity.
Tim Reynolds, Chair of The National Museum of Computing, said: "The achievements of those who worked at Bletchley Park are humbling. 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.
"The working Colossus rebuilt by the late Tony Sale 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.
"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."
A Short History of Colossus
German teleprinter signals encrypted by Lorenz machines were first heard in Britain by police officers on the south coast listening for possible spy transmissions in 1940.
In August 1941, a procedural error by a German operator enabled Colonel John Tiltman, a top code-breaker at Bletchley Park, to decipher a message.
Brilliant mathematician Bill Tutte began working on the case and was able to deduce the complete logical structure of the cipher machine which we now know as Lorenz.
Code-breakers in the so-called Testery, under Colonel Tester, began breaking the codes by hand, but this was very time consuming.
The head of the so-called Newmanry, Max Newman, a mathematician at Bletchley Park, believed certain aspects of the decryption process could be automated. Initially, electro-mechanical Robinson machines (named after the cartoonist Heath Robinson) were used to find the start positions of the Lorenz wheels to speed up code-breaking. But the Robinson machines had shortcomings.
Tommy Flowers, an ingenious Post Office electronics engineer at Dollis Hill, was asked to improve upon the Robinsons, but instead designed Colossus, the world's first electronic computer which enabled the Lorenz start-wheel positions to be found in a few hours, thereby greatly shortening the code-breaking process and enabling larger numbers of messages to be broken.
Colossus Mark I began operating on 5 February 1944, and was succeeded in June of that year by the Mark II. By the end of the war there were ten functioning Colossi working around the clock helping to decipher the messages of German High Command.
The deciphered messages provided the Allies with crucial intelligence on what enemy armed forces were plotting. The allies knew for example that Hitler had swallowed the bait that the D-Day landings in June 1944 would be at Calais rather than Normandy. This gave the Allies a decisive advantage.
As a direct result of Colossus, the war was shortened and countless lives saved.
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.
In honour of the men and women who worked at Bletchley Park during World War II, Tony Sale, co-founder of The National Museum of Computing, led a team to rebuild Colossus in 1994. The idea of the rebuild came to him after snippets of information had emerged about the machines in the 1970s and 1980s.
With eight photographs of Colossus taken in 1945, the ambitious project was under way. A few circuit diagrams kept by engineers who worked on the original computer were also obtained.
On 15 November 2007, a rebuilt fully-functioning Colossus Mark II was unveiled to the public at The National Museum of Computing located on Bletchley Park. On 6 March 2012, the Colossus Rebuild was presented in a new extended Colossus Gallery and visitors were able to walk around the enormous machine for the first time.
Today the Colossus Rebuild provides a hugely popular working exhibit drawing visitors and media from across the globe. In TNMOC's educational programme for schools and colleges, it inspires young people to become the engineers and computer scientists of the future.
The rebuild of the Tunny machine was begun by Don Skeggs in the early 1990s in conjunction with the start of the rebuild of Colossus. Work on Tunny was suspended after a few years, but was restarted by a team led by John Pether and John Whetter in 2005.
As with the Colossus Rebuild, key components for the Tunny reconstruction were salvaged from decommissioned analogue telephone exchanges, kindly donated by BT.
Tunny was completed and presented in a new Tunny Gallery at The National Museum of Computing on 26 May 2011.
A TNMOC team is currently engaged in recreating one of the Robinson machines.