The Colossus Decrypting Computer
First Used in January 1944, and Successful on First Use

People imagine the Bletchley Park enterprise as a bunch of guys sitting around with pencil and paper, getting clever ideas. Alan Turing staring into space. Not entirely. Here is one of the clever ideas in a form beyond the pencil and paper original: the original Colossus decrypting computer. Its successful deployment meant the reliable and rapid reading of German naval codes. This in turn solidified Allied control of the Atlantic, as a precondition for the Normandy invasion of June 1944. Colossus used rapid optical input (5,000 characters per second; the paper tape feed is visible in the picture) as well as extremely sophisticated decrypting circuitry, applied thousands of times to the message once input. It was by far the most advanced thing of its kind at the time. (Its nearest American counterpart, the ENIAC fast arithmetic machine, which was intended for the computation of artillery tables, did not become operational until 1946, too late to play a part in the intelligence wars). Ten Colossus machines were built for Bletchley Park. Eight were destroyed at war's end in August 1945, and the remaining two in the 1960's. Their progeny are everywhere, including the thing which is sitting in front of you as you read this.

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