The computers that won the war: Bletchley Park's codebreaking equipment is rebuilt


The preparation of message tapes using a Perforator

Source:  Robert Dowell, TNMOC

The preparation of message tapes using a Perforator

For Bletchley Park to analyse and process the cipher text, it had to be transferred to perforated paper tape at Knockholt. This was done manually by a slip reader who would type the cipher text letters into a perforator machine. The message tape would be checked and double-checked against the slip to ensure that there were no more than six errors in 1000 characters, which was the limit set by Bletchley Park. Once an accurate tape had been produced, it was sent to Bletchley over two separate landlines where it was received on two re-perforators and the two tapes checked again for errors.


The Tunny Gallery, opened at The National Museum of Computing at Bletchley Park on 26 May 2011, tells the incredible story of the interception and decryption of German High Command radio teleprinter messages during World War Two. The gallery shows the entire wartime code-breaking process from intercept to decrypt and recognises the remarkable achievements of the men and women who contributed to the process in the 1940s. The centrepiece of the gallery is a fully functioning rebuild of a Tunny machine that produced the final decrypts of enciphered communications of the German High Command. The original Tunny, a British re-engineering of the then-unseen German Lorenz S42 cipher machine, was completed in 1942.

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