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The Crown Inn, where Alan Turing lodged
(my photo, 1979)
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Alan Turing at War
After Britain declared war on Germany on 3 September 1939, British codebreaking operations were moved from London to Bletchley Park. This country house was near the then small railway town of Bletchley, half-way between Oxford and Cambridge.
See this modern map for the site, close to Bletchley railway station.
Between 4 September 1939 and the summer of 1944, Alan Turing lodged at The Crown Inn, at Shenley Brook End, a village to the west of Bletchley.
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The Shenley area (see this map)
is now completely
changed. | War did not stop Alan Turing being an individualist. In 1940 he buried some silver bars near Shenley. In 1944, 1946 and 1952 he tried to find them and failed. No-one knows what happened to his buried treasure! |
Bletchley Park Mansion |
Bletchley Park today
Bletchley Park can still be seen today because the wartime site was left largely unchanged after 1945.
In 1991, the site was saved from property development, and amazing work of reconstruction was done by the original curator, Tony Sale, and his collaborators.
Now the house and grounds are managed by the Bletchley Park Trust.
There has been much controversy over the conservation of the site. In 2005, English Heritage published a detailed report on its value.
In August 2008, the Independent newspaper took up the cause of saving it. See this article and a further one.
The long-term future is still insecure. See the Government statement of 2009, and a later grant from the National Lottery.
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The Bletchley Park Trust website gives full details of how to visit the museum and the various events held there. It has a
history section.
It is hoped to create an
Alan Turing Science Centre at the site, thanks to a large American donation. |
Tony Sale manages a complementary website, www.codesandciphers.org.uk,
which gives extensive technical explanation and copies of original documents.
It also gives a Virtual Tour of Bletchley Park with many photographs. See also the Codes and Ciphers Heritage Trust. |
The huts: my photo, August 1998. | The nerve centreEverything to do with intelligence was dominated by the technicalities of the Enigma cipher machine, the key to German communications.
Alan Turing's wartime life was spent mainly in the Huts erected in the grounds of Bletchley Park, where the technical work of codebreaking was done.
Hut Eight, where Alan Turing worked on the naval Enigma, is in the centre of the picture. To the left is Hut Six (Army and Air Force signals). To the right is Hut One. This is where, in 1940, the first Bombe, Turing's codebreaking machine, was installed. |
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The Enigma
Most German communications were enciphered on the Enigma
cipher machine. It was based on rotors whose movement produced ever-changing alphabetic substitutions.
In its military use, the basic machine was greatly enhanced by a plugboard, visible on the front of the machine.
The ciphers it produced were supposed to be unbreakable even by someone in possession of the machine. Ideas of great logical ingenuity were needed to defeat it.
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If you want to see an Enigma in real life, this page by
David Hamer tells you some locations. If you are Bill Gates, you may like to
buy one.
Cheaper: a modern replica.
Even cheaper: this on-line simulator by Dirk Rijmenants, with elegant and realistic graphical layout and a challenge.
The Enigma has become an icon and a cult object in its own way. This is explored in a book by Dominik Landwehr (in German): Mythos Enigma.
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Who broke the Enigma?
In fact, the Enigma had to be broken afresh over and over again. The hardware in the picture is not the whole story, and capturing it did not allow Enigma messages to be read. The German use of the Enigma depended on systems for setting the keys for each message transmitted, and it was these key-systems that had to be broken. There were many such systems, often changing, and the hardware was changed as well from time to time. The brilliant pre-war work by
Polish mathematicians enabled them to read Enigma messages on the simplest key-systems. The information they gave to Britain and France in 1939 may have been crucial, but it was not sufficient for the continuation and extension of Enigma breaking over the next six years. New ideas were essential.
In 1939-40 Alan Turing and another Cambridge mathematician, Gordon Welchman, designed a new machine, the British Bombe. The basic property of the Bombe was that it could break any Enigma-enciphered message, provided that the hardware of the Enigma was known and that a plain-text 'crib' of about 20 letters could be guessed accurately. |
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The cottage in the stable yard of Bletchley Park, where Alan Turing worked in 1939-40.
(My photo, July 2002). |
Alan Turing made a brilliant contribution to the design with an idea that he himself related to the principle in mathematical logic that 'a false proposition implies any proposition.' It was this idea that overcame the apparently insuperable complication of the plugboard attachment. But that idea was just the beginning of a continuous struggle.
The work done by Turing and his colleagues at Bletchley Park brought cryptology into the modern world. It required ingenious logic, statistical theory, the beginnings of information theory, advanced technology, and superb organisation.
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Totally secret for thirty years
Everything about the breaking of the Enigma cipher systems remained secret until the mid-1970s. Partial accounts then emerged constrained by continuing secrecy about technical matters. Gordon Welchman gave the central principle of the Bombe in describing his own contribution in The Hut Six Story, 1983. In the mid-1990s virtually everything was released from secrecy and now it is possible for scholars to investigate this fascinating history in considerable detail.
Recent books are:
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Hut 6, Bletchley Park, where the German Air Force signals
were broken with the help of Turing's Bombes.
(My photo, 1998) |
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Simon Singh's popular work The Code Book claims to explain 'how Turing broke the Enigma.' Unfortunately it makes the Enigma problem look much easier than it actually was, and so undervalues Turing's contribution.
Mark Baldwin offers illustrated talks and an extensive specialist book service.
Station X
The television programme series Station X about Bletchley Park, made for Channel Four television in the UK, was first transmitted in early 1999.
The video can be bought on-line from the Bletchley Park Shop. For the United States it was reduced to a two-hour programme shown on Nova as Decoding Nazi Secrets. It is evocative and valuable as a archive of interviews but weak in showing that the secret of success at Bletchley Park was the application of scientific method. Michael Smith's book, Station X, accompanied the TV series.
Other sites on World War II cryptography
Frode Weierud's CryptoCellar
Geoff Sullivan's Crypto Barn
The Imperial War Museum has a sequence of pages on codes and ciphers which is not, however, entirely accurate (it says that the Colossus machine was used for deciphering Enigma.)
A series of articles on the uses of deciphered Enigma information.
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Alan Turing and the Battle of the Atlantic
The Bombe was used with success from the summer of 1940 onwards, to break messages enciphered on the simpler Enigma system used by the German Air Force. But the most important messages were those to and from the U-boat fleet, and these were enciphered on a much more secure Enigma system. Alan Turing took on this problem, going against the prevailing view that it would prove unbreakable. Although he had crucial new ideas at the end of 1939, not much practical progress could be made. In 1940 they were desperate.
See the October 1940 Operation Ruthless plan devised by Ian Fleming, later the creator of 'James Bond', to capture such information for Turing's work.
The breakthrough came in February 1941, with the capture of papers from the Krebs off Norway.
From then on, with the help of some further captures, the U-boat communications were effectively mastered. Alan Turing continued to head the cryptanalysis of all German Naval signals in Hut Eight.
The naval Enigma was more complicated than those of the other German services, using a stock of eight rather than five rotors. For the Bombe to work in a practical time it was necessary to find ways of cutting down the number of possibilities. Alan Turing developed 'Banburismus,' a statistical and logical technique of great elegance, to find the identity of the rotors of the enciphering Enigma before using the Bombe. Turing made major developments in Bayesian statistical theory for this work, with his assistant (I. J.) Jack Good.
See this news article about recent work extending Turing's theory, with more technical web-page and downloadable pdf on 'Almost Good Turing.'
See Steve Hosgood's page 'Banburismus' for a very detailed description of the whole process.
Tony Sale also has a sequence of pages on Naval Enigma explaining in considerable detail what Alan Turing did and how Banburismus worked.
Books concentrating on the naval Enigma capture operations:
On 1 February 1942, the U-boats changed to an even more complicated Enigma system, involving a fourth rotor. Their communications became unbreakable until December 1942, when a brilliant trick allowed codebreaking to be restored.
Fact and Fiction
An American film, U-571, drew on the story of the material captured in 1941 but fictionalised it as an American achievement. You can see US Navy comment on this fictionalisation here.
Robert Harris's thriller novel Enigma has been adapted as a film Enigma with a screenplay by Tom Stoppard. It depicts the naval Enigma problem in the 1943 period. However the story is fiction, and the film does not show the actual Bletchley Park location. The film also endows the fictional lead character with allusions suggesting he is 'really' Turing himself. See my review of the film. However, more care was taken in representing the technical background.
You can see in Tony Sale's detailed pages how he scrupulously devised suitable messages and Enigma methods for this film.
Still being broken
U-boat messages that Bletchley Park were unable to break are being attacked successfully today: see the M4 Message Breaking Project and this BBC news item about it.
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The end of the beginning
At the end of 1942, Alan Turing's war experience had changed him in many ways.
- It made him a top level liaison between the United Kingdom and the United States. Go to
the next Scrapbook page.
- It made him an enthusiast for 'intelligent machinery'. Go to a further Scrapbook page for an outline of how Turing started the Artificial Intelligence program.
- It gave him experience of digital electronics. Go to a further Scrapbook page to see what happened next with the codebreaking technology.
All these developments were to come together in the post-war world of the computer, with Alan Turing at its centre. But no-one knew it was...
The beginning of the end
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