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Celebrating the 70th anniversary of Colossus, the WWII codebreaking machine

Caroline Baldwin

The National Museum of Computing is celebrating the 70th anniversary of Colossus, the computer which broke the code used to encrypt secret messages between Hitler and his generals in World War Two.

The Colossus machine attacked its first Lorenz-encrypted message on February 5 1944.

Operating_Colousus.jpg

Today, Colossus veterans and their families will gather at The National Museum of Computing to celebrate the machine’s 70th anniversary with a demonstration of the rebuilt machine.

Designed by the engineer Tommy Flowers, Colossus was built to accelerate codebreaking. By the end of the war there were ten functioning computers.

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.

Colossus was the first electronic programmable computer, but for 30 years after the war, its existence was kept secret by the government.

Colossus - a machine like no other

The Colossus was 7ft high by 17ft wide and 11ft deep. It weighed five tons 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 7km of wiring. Reading 5,000 characters per second (faster than anything ever produced commercially), Colossus decrypted 63 million characters of high-grade German messages by the end of the war.

Back in the 1970s, Brian Randell, emeritus professor at the School of Computing Science at Newcastle University, lobbied then prime minister Edward Heath for the Colossus to be revealed to the world.  

But Heath replied that the Colossus programme could not be declassified, citing considerations of the national interest. 

But Randell persisted, with a XX year efforts to make the machine a living memory. While the BBC identified Colossus as a "codebreaker" in 1977, it wasn’t until 2003 that the Cabinet Office fully declassified the Colossus programme.

In the 1990s Tony Sale, co-founder of The National Museum of Computing, led the rebuild of the Colossus codebreaking computer.

Armed with only eight photographs taken in 1945 and a few circuit diagrams kept by engineers, Sale and his team successful rebuilt a fully-functioning Colossus Mark II, which they revealed in 2007.

The machine is now the main attraction at the National Museum of Computing, based on the grounds of Bletchley Park. The rebuild is now situated in the Colossus Gallery, which allows visitors to walk around the enormous machine.


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