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Bletchley Park resurrects code-cracking antique

The National Museum of Computing at Bletchley Park has unveiled a new display area which houses a fully functioning rebuild of a Tunny code-breaking machine.

The device produced the final decrypts of enciphered communications sent by the German High Command during the Second World War. The original Tunny, a British re-engineering of the then unseen German Lorenz S42 cipher machine, was completed in 1942.

After tens of thousands of man-hours and with only fragmentary information about the original, the rebuilt and functioning Tunny has recently been completed by a team at the museum.

Andy Clark, a trustee and director of TNMOC, said: "The work of the team led by John Pether and John Whetter is fantastic and, we hope, a fitting tribute to the achievements of the wartime codebreakers. We can now present the whole process of code-breaking as it happened during World War II in the historic Block H on Bletchley Park.

"The completion of the Tunny rebuild superbly complements the rebuild of Colossus by Tony Sale’s team in 2007 and will undoubtedly attract even more visitors to the array of fascinating working vintage computers at TNMOC."

Wartime code-breaker Bill Tutte used a few encrypted and decrypted messages to deduce the workings of the German’s Lorenz cipher machine, a device that he had never seen. His deductions were so accurate that the first reverse-engineered Tunny machine was able to start decoding messages in 1942 using wheel settings found manually.

In early 1944, the development of the Colossus computer provided Tunny with the wheel settings in a matter of hours and reduced the total job deciphering a message from several weeks to up to four days.

By the end of the war, the Tunny machines are thought to have numbered between 12 and 15, operated continuously and were probably located in Block F at Bletchley Park, a short distance from Block H where the Colossus computers were housed. The Tunny machines were dismantled and recycled after the war.

The original Tunny, though technically not as significant as the development of Colossus (now generally recognised as the world’s first modern computer), was a remarkable feat in its own right and absolutely essential in the process of decoding of Lorenz-encrypted communications.

The rebuild of the Tunny machine started in the early 1990s, was suspended after a few years, and restarted in 2005. Key components for the rebuild were salvaged from decommissioned analogue telephone exchanges donated by BT.