Bletchley Park Tour

Colossus: the world's first computer

Enigma, although probably the most famous, was by no means the only cypher to be broken at Bletchley Park. Lorenz was a highly sophisticated cypher used personally by Hitler and his High Command. As D-Day approached, breaking 'Tunny', as Lorenz was known, was to become increasingly important.

Colonel John Tiltman and Bill Tutte managed to work out how the Lorenz machine operated, despite the fact that no one at Bletchley Park had ever seen one.

But many of the Tunny messages still took several weeks to decypher; far too long for the intelligence to be of use. Mathematician Max Newman became convinced that the answer lay in building a computing machine such as that described in a pre-war thesis by Alan Turing.

The first attempt, named 'Robinson' after the designer of cartoon contraptions Heath Robinson, worked on the principle that no machine can generate a truly random sequence of letters. Robinson was a partial success but it depended upon the high-speed synchronization of two streams of paper tape. The paper kept ripping.

Enter Tommy Flowers, who built an electronic machine with thermionic valves (vacuum tubes) to do the same job as Robinson but without the need for the synchronization of the tapes. The result was Colossus, the world's first programmable electronic computer and a crucial contributor to the success of D-Day.

With the development of Colossus, Bletchley Park changed the way the world communicates.

You can see a working rebuild of Colossus in Bletchley Park's museum. Please note: Closed for relocation until further notice.

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