Bletchley veterans take front seat as Colossus codebreaker springs back to life

By Richard Moss | 06 June 2016

Veterans from the codecracking compound at Bletchley Park say retracing their heroics is an "incredible" experience on the anniversary of D-Day

a photo of a group of seated elderly ladies with a WWII re-enactor in front of a large computer
Colossus veterans (left to right): Irene Dixon, Lorna Cockayne, Shirley Wheeldon, Joanna Chorley, Margaret Mortimer and (standing) Jacqui Garrad, of TNMOC, in front of the Colossus Rebuild© Mark Crick / National Museum of Computing
“Of course, we had no idea how important these messages were at the time. It was decades later that we Wrens came to understand the significance of what we were doing.”

The words of Irene Dixon, a former Womens Royal Naval Service operator of the codebreaking computer Colossus at Bletchley Park, offer a sober view of the groundbreaking work of the codebreakers of British intelligence to break Lorenz, Hitler’s most secret cipher, in the run-up to D-Day on June 6 1944.

Irene was one of a handful of veterans who this weekend returned to the site of her secret wartime service for a full re-enactment at the Bletchley-based National Museum of Computing, recreating their work on the Colossus codebreaking machine.  

The cracking of the top-secret Lorenz messages of German High Command is today credited with shortening the war and saving countless lives from D-Day onwards.

Much more complex than Enigma, the Lorenz cipher (called Tunny in Britain) was broken thanks to the codebreaker and mathematician Bill Tutte, who cleverly deduced the principles of a Lorenz machine without ever having seen one. As a result, the Allies were routinely able to read German High Command’s top secret messages.

a photo of a woman in WWII WRNS dress pulling a sheet of paper out of a typewriter style machine
A re-enactor takes the wheel settings sheet discovered by Colossus© Mark Crick / National Museum of Computing
From 1944, with the creation of the Colossus computer by the brilliant British engineer Tommy Flowers, the Allies were able to reduce the decrypt time from weeks to hours - a speed that effectively undermined the German military machine.

And it was WRNS servicewomen like Irene and her colleagues who operated the equipment used in making and breaking Lorenz at a crucial time in the war.

Intelligence gained from the breaking of the cipher was highly significant at several points during the war, especially during the run-up to D-Day on 6 June 1944, when the Allies realised that the deception of where the landings might be had been successful.

For Irene, who was one of the guests on hand at Bletchley to witness the full "end to ends" re-enactment of the codebreaking process, her work was all the more poignant.
“I didn’t know it at the time, but my future husband was on his way to Normandy as part of the D-Day landings,” she explains. “The messages that, as a Colossus Operator, I was helping to decipher were vital in telling the Allies that Hitler thought the landings would be elsewhere.

“To see it all remembered and demonstrated today is incredible."

a photo of a woman with a 1940s hairdo in front of a large bank of computers
Side-by-side: the Lorenz SZ42 used in Germany-occupied territories and the reconstructed Tunny machine that decrypted the messages at Bletchley© Mark Crick / National Museum of Computing
For twenty years, volunteers at the museum have researched and worked meticulously to reconstruct the British equipment used in the Breaking of Lorenz from intercept to decrypt. Now, with some recently acquired original equipment, the Museum is also demonstrating the other side: how the messages were encrypted and transmitted in German-occupied territories.

The newly arrived equipment representing the German operations includes an original Lorenz SZ42 encryption device, on long loan from the Norwegian Armed Forces Museum, a 1943 German military teleprinter and a Spruchtafel used to determine the starting positions of the rotors of the Lorenz SZ42 for each message.

Andy Clark,  the Chairman of the museum, said it was the first time all the equipment been seen together and demonstrated under one roof.

“Thanks to the incredible work of TNMOC volunteers, the full story can now be seen daily by the general public,” he added. “And it is fitting that the location is Block H, the world’s first purpose built computer centre, the home of Colossus, on Bletchley Park.

“For decades this story could not be revealed to the public. Yet its impact during wartime and post-war society has been huge and resonates to this day.

"The technologies at the core of the Breaking of Lorenz – encryption, communications and computing – are at the very heart of our modern world, so the narrative is as relevant today as it was then and an inspiration to the next generation of computer scientists and engineers.”

a photo of two men in khaki coveralls and a third in British WWII battledress
Museum volunteers John Watson, John Pether and Charles Coultas were part of the team responsible for the reconstructions and restorations in the workshop with the Lorenz SZ42© Mark Crick / National Museum of Computing
The complex Colossal rebuild was led by the late Tony Sale, who began a reconstruction of a Colossus computer at The National Museum of Computing in 1994.

Five surviving Colossus Wrens, a female Colossus wireman and relatives of key figures in the Breaking of Lorenz were all on hand to see the full re-enactment.

  • The Colossus and Tunny Galleries are open daily. The whole Museum is currently open to the public from 12 noon on Thursdays, Saturdays and Sundays, spring and summer Bank Holidays and during school holidays. Visit

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