Bletchley Park WWII Code-breaking Machines Rebuilt from Memories
May 30, 2011 1:55 PM   Subscribe

Early 1940: British police listening for radio transmissions from German spies within the UK pick up weird signals, and pass them to Bletchley Park, the United Kingdom's main decryption establishment in WWII. The source of these German messages is an unknown machine, which the Brits dub Tunny (10 minute video with Tony Sale describing the Tunny). August 30, 1941: German operators send two very similar messages with the same key, providing insight into the encryption scheme. By January 1942, British cryptographers deduced the workings of the German code machines, sight unseen. The British were able to create their own Tunny emulators to decrypt messages sent by German High Command. After the war, these and other British code-breaking and emulating machines were demolished and/or recycled for parts and their blueprints destroyed, leaving a hole in the history of the British WWII code breaking. Efforts to rebuild the British Tunny emulator started in the 1990s, and quite recently a Tunny emulator replica was completed.

The German military had a number of different encrypted communications systems, from the relatively simple modified German military version of the commercially-available Enigma machine (Google Quickview / PDF). The more complex systems were based on teleprinters (wiki).

The Germans had three different types of teleprinter cipher machines (Google Quickview / PDF) : three models of the Lorenz system, dubbed Tunny by the British; various models of the Siemens & Halske Schlüsselfernschreibmaschine (SFM), named Sturgen by the British; and the Siemens T43, which may have been the unbroken system nicknamed Thrasher. Tunny was used by the German army, while Sturgen was used by the navy and air force. The German nickname for the special teleprinter equipment was Sägefisch (sawfish), which is the source of the Fish nickname in England, and the subsequent fish-related nicknames for specific systems.

When the British first found the "fish" messages, they realized these communications were quite important messages. The first break in Tunny came on August 30, 1941, when a German operator missed a message on first transmission and asked, in plaintext, that the message be re-sent. The key setting was the same and the message was largely similar, allowing British cryptographers to figure out the operations of the cipher machine without seeing it. About five months later, the Tunny emulator was built, allowing cipher text to be decrypted, once the decoding settings were figured out by hand.

The first attempt to speed up the process was Heath Robinson, a mechanical method of figuring out the decoder settings. The second is the world's first programmable electronic computer, Colossus, and made by Thomas Harold Flowers (MBE) at the Dollis Hill Post Office Research Station. A number of Colossi were built, and all of these machines were dismantled at the end of the war, to guard against their secrets becoming known.

By finding scraps of information and picking the memories of those who made and worked with the machines With the re-creation of the Tunny emulator, Bletchley Park once again has a complete set of re-created decrypting machines (photos of the exhibit at The National Museum of Computing, itself located at Bletchley Park).

More interesting details and rabbit trails:
* The Fish and I, Professor William T. Tutte's paper on FISH, as presented at the opening ceremony of Centre for Applied Cryptographic Research at the University of Waterloo. This paper is just one of the many fascinating features at Frode Weierud's CryptoCellar.
* WW II Codes and Ciphers, Tony Sale's website on the Colossus and Tunny rebuild efforts, Enigma, and other related topics.
* An introduction to Bletchley Park, a 2008 MetaFilter post.
posted by filthy light thief (12 comments total) 70 users marked this as a favorite
See also: NOVA Transcript from the 1999 episode Decoding Nazi Secrets
posted by filthy light thief at 1:57 PM on May 30, 2011

See also: eriko's great comment explaining the WWII origins of operational code names (eg "Odyssey Dawn") in the cryptography war between England & Germany.
posted by UbuRoivas at 2:01 PM on May 30, 2011 [2 favorites]

A man after my own heart. Great post, flt.
posted by spiderskull at 2:20 PM on May 30, 2011

Excellent! I can't get enough of this sort of thing.
posted by BungaDunga at 5:12 PM on May 30, 2011 [1 favorite]

What a fantastic post. This is going to take a while to get through. Thanks!
posted by dazed_one at 6:43 PM on May 30, 2011

Meanwhile, somewhere beneath Berlin, a lone T43 chatters nonsense onto its rusting platen.
posted by Kikkoman at 8:43 PM on May 30, 2011

The way so much of the stuff achieved at Bletchley Park was wiped, destroyed and/or hidden when the war was over is really criminal. I blame Churchill's love of dramatic gestures.
posted by Segundus at 11:53 PM on May 30, 2011

Shame it's not a unique occurrence - a lot of our engineering history has simply been wiped from the planet, normally by chucking it in the Irish Sea. The TSR-2 being a prime example.
posted by sodium lights the horizon at 1:29 AM on May 31, 2011

Great post, filthy light thief. I've been to Bletchley Park a few years ago, and it's an amazing day out for anybody with a passing interest in the subject. At the time they were still building a replica Colossus. Looks like it's time for another visit!
posted by salmacis at 3:06 AM on May 31, 2011

Awesome post. I'll remember this next time I'm getting my ass kicked by a Sudoku puzzle.
posted by double block and bleed at 6:39 AM on May 31, 2011

Damn ... the audio in that video must have been decoded with the wrong machine ... top 5 worst ever audio tracks (left channel only for starters!)

Otherwise, bravo!

Since it ties in, might as well mention that next year is the Turing centenary; some viewers may wish to follow that on the site (news, a year-full of planned events, email list) or at Twitter.
posted by Twang at 1:07 PM on May 31, 2011

A number of Colossi were built, and all of these machines were dismantled at the end of the war, to guard against their secrets becoming known.

Not quite. Although those were Churchill's orders, at least two machines were saved. They were moved to the newly created 'Government Communications Headquarters' (GCHQ) in Eastcote and then moved again to Cheltenham where at least one remained in operation until 1959.

What were they doing? According to Jack Copeland in Colossus, it's not entirely clear, however those now at Bletchley Park believe that they were used to decrypt Soviet messages sent using Lorenz (Tunny) machines captured at the end of the War.

If the Soviets were using captured Lorenz machines, it may have been to play games with the British and Americans. Churchill never revealed to Stalin that the Lorenz code had been broken (he did share that the Enigma codes were broken on a regular basis). It was believed that this was one of the last, great secrets of World War Two. The British might well have believed the Russians were using captured Lorenz machines, confident that they were secure.

They would have been wrong. Stalin had a mole in Bletchley Park, at the heart of the Colossus project, right from the beginning. He was receiving direct intercepts from the start.

All good fun. Bletchley Park is a marvellous day out and the volunteers at the National Museum of Computing are superb guides. To see Tony Sale demonstrate Colossus is unforgettable, here's a rather shaky video which gives a flavour of a truly great man, and an extraordinary achievement.

I can't put aside the image of Alan Turing cycling from Bletchley Park to London wearing a Gasmask.
posted by grahamwell at 7:04 AM on June 2, 2011 [1 favorite]

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