Colossus computer

The working rebuild of a Colossus Mark 2 at Bletchley Park, seen from the back, where the racks of glowing vacuum tubes do the counting. Tommy Flowers designed Colossus to attack the German Lorenz teleprinter cipher, and the first machine was working at Bletchley Park in 1944. Ten were delivered by the end of the war, each with up to 2,500 tubes. It read its messages from punched paper tape and was built for one code-breaking job rather than general calculation, but it proved that thousands of tubes could run reliably together, which is the lesson every machine after it built on.