Colossus Mk2, a wartime code-breaker hailed as one of the first electronic computers, has been rebuilt and reunited with Bletchley Park veterans. At Bletchley, the hub of British code operations, it crucially found the keys to break the Lorenz code used by Hitler to encrypt messages to his generals. Colossus Mk2 has been painstakingly put back together over a decade by computer conservationists for Bletchley museums. As part of D-Day celebrations, 30 war coders gathered to see it once more.

Besides its code-breaking prowess, Colossus was one of the most significant forerunners of computing technology because it was programmable and electronic. Colossus Mk2 was essentially an upgrade of Mk1, which went into action on 1 February 1944. It was a prototype machine which proved the concept of electronic switching.

Electronics made it a very different creature to other code-breaking machines, which carried out blind searches for text matches. "The major thing was it implemented a statistical attack on a cipher and that was the first time that was done," Tony Sale, head of the Colossus Rebuild Project, told BBC News Online. "To do that it had to repeatedly scan the messages very fast, and a large amount of messages. Because it was electronic, it was able to do that very fast."

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