Tunny rebuild completed

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TNMOC displays the entire codebreaking process from signal intercept to final decrypt by Tunny

BBC News Online video at the opening

Four World War II codebreakers will be present at the opening of the new Tunny Gallery at The National Museum of Computing today. 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.

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 National Museum of Computing.

The design of the original Tunny machines was the result of the ingenuity of a team led by Bill Tutte who worked in the Testery at Bletchley Park. Tunny was a re-engineering of the Lorenz SZ42 cipher machine used in radio teleprinter communications amongst the German High Command. No-one at the Testery saw the Lorenz until one was captured after the war, so Tutte had to work out the logical structure of the highly sophisticated 12-rotor machine using samples of its encrypted output and the manual decrypts laboriously and ingeniously achieved by the Testery. The 12 rotors of the Lorenz machine gave it 1.6 million billion possible start positions, so the work of the Testery was an astonishing achievement.

Built by the Post Office Research Station at Dollis Hill in London, Tunny started its first decrypts in 1942. When Colossus was completed in 1944, it supplied the wheel settings much more quickly than the earlier ‘Robinson’ machines, and the number of Tunny machines was increased to between 12 and 15. By the end of the war, they were working around the clock deciphering about 300 messages a week to gain vital intelligence.

Today a team led by John Pether and John Whetter has rebuilt a fully operational Tunny machine based on fragmentary evidence consisting of a few photographs, partial circuit diagrams and the fading memories of a few original Tunny operators.

John Pether said: “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.

“Sourcing 200 suitable relays and dealing with the complex wiring schedules was difficult, but we really got in tune with the original team when we had to set up the electronic timing circuits. They were a continuous source of problems then as they are even now for the rebuild team – except the original team didn’t even have the benefit of digital storage oscilloscopes!”

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.”

Notes To Editors

The original Tunny machines

In the Bletchley Park Testery, 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 Tunny machine was able to start decoding messages in 1942 using wheel settings laboriously found by hand, sometimes with the help of the sluggish and somewhat unreliable Robinson machines. 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 Tunny Rebuild

The rebuild of the Tunny machine was begun by Don Skeggs in the early 1990s in conjunction with the start of the rebuild of Colossus. Work on Tunny was suspended after a few years, but was restarted by a team led by John Pether and John Whetter in 2005.

The rebuild was in four stages: the one-wheel Tunny to ensure that timing circuits and relays worked properly, followed by the five-, seven- and twelve-wheel Tunny. At each stage, the rebuild was tested to ensure that it had been completed successfully.

As with the Colossus rebuild, key components for the Tunny rebuild were salvaged from decommissioned analogue telephone exchanges, kindly donated by BT.

About The National Museum of Computing

The National Museum of Computing at Bletchley Park, an independent charity, houses the largest collection of functional historic computers in Europe, including a rebuilt Colossus, the world’s first electronic programmable computer.

The Museum complements the Bletchley Park Trust’s story of code breaking up to the Colossus and allows visitors to follow the development of computing from the ultra-secret pioneering efforts of the 1940s through the mainframes of the 1960s and 1970s, and the rise of personal computing in the 1980s. New working exhibits are regularly unveiled and the public can already view a rebuilt and fully operational Colossus, the restoration of the Harwell / WITCH computer, and an ICL 2966, one of the workhorse mainframes computers of the 1980s, many of the earliest desktops of the 1980s and 1990s, plus the NPL Technology of the Internet Gallery. In June 2010 TNMOC hosted Britain’s first-ever Vintage Computer Festival.

Funders of the Museum include Bletchley Park Capital Partners, InsightSoftware.com, PGP Corporation, IBM, NPL, HP Labs, BCS, Black Marble, and the School of Computer Science at the University of Hertfordshire.

The Museum is currently open on Thursdays and Saturdays from 1pm, and on Bank Holidays in spring and summer. Guided tours are also available at 2.30pm on Tuesdays, Sundays and some other days. Groups may visit at other times by arrangement and special organisation Away-Days can be booked.

For more information, see www.tnmoc.org and follow @tnmoc on Twitter and The National Museum of Computing on Facebook.

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