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Colossus computer

Colossus was the name for any of at least two versions of the world's first programmable electronic computer. It was built by British Post Office at its Dollis Hill facility by Thomas Flowers and crew to a design by Max Newman and associates of Bletchley Park. It was designed in an attempt to break one or more of the Fish cyphers[?] (a Bletchley Park term) used by the German military for its most secure strategic communications. These were essentially attempts at an electro mechanical implementations of the one-time pad cypher invented by Gilbert Venam and Joseph Mauborgne in the US. The most important was a teletype based machine built by Lorenz Electric. Another, different machine was designed and built by Siemens. The Germans referred to one of them as the Geheimfernschreiber[?].

The one-time pad _requires_ a random sequence. It is combined with the plaintext (character by character) resulting in the cyphertext which is transmitted. On receipt, the same random sequence is combined with the cyphertext (again character by character), and because the combining operation is reversible in a particular way (see XOR) the output is the original plaintext. In the Lorenz machine, the 'random' sequence was produced by various electromechnaical rotors, and wasn't actually random. Because there were patterns, they could be predicted if the cryptanalysts were sufficiently clever, and plaintexts recovered. In the case of the Lorenz machine, Col John Tiltman and Bill Tutte were sufficiently clever.

The idea for Colossus developed out of a prior project which produced a special purpose comparator machine called the Heath Robinson. The Colossus was intended to be more flexible and faster; it was decided to make it programmable in a way the Heath Robinson had not been. The project was headed by the mathematician Max Newman. It started early in 1943 and the first version of the machine (Mark 1 Colossus) started working in January 1944, to be followed by the improved Mark 2 Colossus in June 1944. Ten Mark 2 Collossus machines were in use at Bletchley Park by the end of the war.

The machine used vacuum tubes and read a cyphertext from a paper tape and then applied a programmable logical function to every character, counting how often this function returned "true".

It was a highly secret device, and had therefore not much influence on the development of later computers. Nearly all documentation and machinery was classified immediately after the war, and destroyed in 1960s. It is said that Winston Churchill specifically ordered the destruction of the Colossus machines into 'pieces no bigger than a man's hand' and that Tommy Flowers[?] personally burned the blueprints in a furnace at Dollis Hill. Information about Colossus reemerged in the 1970s.

A copy of one of the Colossus versions has been partly completed by Tony Sale and is on display in the Bletchley Park Museum in Milton Keynes, Buckinghamshire.