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Fri, 18 Jan 2019
Overview
75 years since Colossus arrived at Bletchley

On 18 January 1944, the first Colossus machine arrived at Bletchley Park. Just as Bombe machines had been developed to help Bletchley Park’s Codebreakers decipher Enigma messages, Colossus had been commissioned to help break another, even more complex German machine cipher: Lorenz. To tackle Lorenz, Bletchley Park needed Colossus to be capable of statistical analysis, not just to cycle through all possible cipher settings one at a time. A team of General Post Office engineers, led by Tommy Flowers, rose to the challenge. They designed an ingenious system that used electronic valves to store information, making Colossus the world’s first large-scale electronic digital computer.

75 years since Colossus arrived at Bletchley
1 / 10A Lorenz SZ42 cipher machine. The front cover is open to reveal 12 cipher wheels, each of which contains between 23 and 61 settable pins. The wheels worked together in two sets, one set rotating all the time, the other moving intermittently. The wheel settings and rotations worked together to create a complex cipher