Rebuilt Codebreaker Machine Cracked Nazi Secrets in World War II

Tunny Codebreaker

To help break Nazi codes during World War II, British scientists backwards engineered their own version of the German Lorenz encryption machine. Called the "Tunny" machine, the replica code device helped the Allies listen to German communications, and ultimately win the war. Now, modern day code experts have recreated a fully function version of the British "Tunny" machine based on a few photos, partial circuit diagrams and the fading memories of surviving Tunny operators.

The original Tunny machine was created from just a few encrypted and decrypted Nazi messages intercepted by a British codebreaking station at Bletchley Park, England. Mathematician Bill Tutte worked out the logical structure of the German Lorenz cipher machine that sent the messages, despite the fact that the Lorenz machine's 12 rotors meant it had 1.6 million billion possible start positions.

"We’ve succeeded in rebuilding Tunny with scraps of evidence, and although we are very proud of our work it is rather different from the truly astonishing achievement of Bill Tutte’s re-engineering of the Lorenz machine," said John Pether, a computer conservationist at the National Museum of Computing.

World War II Codebreakers

The newly rebuilt Tunny went on display inside the National Museum of Computing at Bletchley Park starting on May 26. [Read more: Computer Interface Technology Through the Ages]

Tunny machines first started their codebreaking work in 1942. The creation of Colossus computers in 1944 supplied wheel settings for the Tunny much more quickly than earlier 'Robinson' machines, and so the Tunny machines could crack codes much faster.

The codebreaking supported the pivotal Allied invasion of Normandy, France, and also helped the Soviets win a crucial tank battle over German forces at the Battle of Kursk.

By the end of the war, the Tunny machines deciphered about 300 messages a week while working around the clock.

Efforts to rebuild the Tunny machine began in the early 1990s to coincide with the rebuilding of the Colossus computer. But the Tunny effort ended up on hold until John Pether and John Whetter restarted it in 2005.

The Tunny rebuild began with just a one-wheel machine to ensure that timing circuits and relays worked properly. The computer conservationists then created a five-, seven- and twelve-wheel Tunny to work their way up to the original.

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