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


Extracting the cipher text with an undulator

Source:  Robert Dowell, TNMOC

Extracting the cipher text with an undulator

At Knockholt, the messages could not be received on a standard teleprinter because of the encryption process. Instead, the output of the radio receiver was fed into an undulator, a high speed recorder. The undulator was a pen recorder which produced a continuous ink trace of the signal on a narrow paper tape called ‘slip’. The tape was read by slip readers who had to memorise the five unit telegraph code and translate the signal trace into letters of the alphabet.


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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