Colossus & the Breaking of Lorenz

The National Museum of Computing

In World War II,  Hitler commissioned an encrypting machine that would be unbreakable.  The Lorenz was used to encrypt teleprinter messages.  Lorenz SZ40s were first used in June 1941, and the SZ42 from mid-1942 onwards.The SZ42 had 12 wheels with different numbers of cams or pins that could produce 1.6 billion different combinations.The Allies did not see a Lorenz machine until after the war but dubbed the machine and its messages "Tunny". Enigma, an entirely different system, was used for operational messages and was much less complex.
First identified as a different type of radio signal by the London Metropolitan Police, Lorenz-encrypted messages were monitored, usually by ATS personnel, at Knockholt in Kent and then transmitted to Bletchley Park for code-breakers to tackle. Reconstruction at TNMOC of receiving station.
Initially Lorenz messages were manually deciphered by linguists and others in the Testery. To demonstrate this in 2014, Captain Jerry Roberts (a Testery code-breaker), at the age of 93, recreated two Tunny (Lorenz) messages in “depth”. A depth was when two messages were sent using the same wheel settings. This gave the code-breakers a potential opening to decipher the message by hand and was how Colonel Tiltman made the first break. Breaking Lorenz codes by hand was a very time-consuming process.
When Bill Tutte had worked out the logical structure of the Lorenz machine, engineers set about building a functionally equivalent machine. Never having seen a Lorenz machine, the device they created looked entirely different and was electro-mechanical rather than purely mechanical. It was made mostly from telephone parts -- components with which the telephone engineers from Britain's General Post Office were most familiar.
To build on the successes of the Testery, attention was focussed on speeding up code-breaking with machines. Headed up by Max Newman, the Newmanry unit created machines that were dubbed Robinsons (after cartoonist Heath Robinson). They were electro-mechanical devices which were able to find the start wheel positions of the Lorenz messages, but they had serious shortcomings.
By this time, breaking of Lorenz messages was becoming routine. The data was transferred onto machine-readable paper tape, a vital process that was difficult and tedious and performed the ATS staff.
 By the end of the war ten Colossus machines were working around the clock to find the start wheels of the Lorenz-encrypted messages. They made a huge impact by accelerating the code-breaking and enabling many more messages to be deciphered. It is sometimes said that the Allies may have been able to read some messages even before Hitler's generals had seen them.The Colossi were operated by WRNS and this photograph, top secret for 30 years, is one of the few existing images of the original computers.  Professor Brian Randell tells the story about how he stumbled across a reference to the existence of  Colossus and how in 1975 that led to the UK government lifting the veil of secrecy surrounding this pioneering computer. 
A short film made by Google to celebrate Colossus and those who built it, in particular Tommy Flowers.
In 1994 a team led by the late Tony Sale began the rebuild of Colossus to commemorate the achievements of the work of Tommy Flowers, Bill Tutte and the men and and women who worked in the wartime codebreaking operations at Bletchley Park. Working with fragments of information, including eight photographs of Colossus taken in 1945 and a few circuit diagrams, the team managed to reconstruct Colossus Mark II. On November 15 2007, a rebuilt fully-functioning Colossus Mark II was unveiled to the public at The National Museum of Computing on Bletchley Park.
The Rebuild of Colossus Mark II stands in the exact location that Colossus No 9 occupied in 1945.
Colossus Valves
A composite picture of some of the 2500 valves of the Colossus Rebuild.
The world's first purpose-built computer centre that housed most of the Colossus computers is now home to the rebuild of Colossus which now occupies the original position of Colossus No 9. The working Colossus Rebuild can be seen daily at The National Museum of Computing. It is a lasting tribute to the men and women whose code-breaking work at Bletchley Park, Buckinghamshire, UK made such a huge impact on the outcome of World War II.
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The National Museum of Computing

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