Rede von Dr David Kenyon
Report: Dr David Kenyon “The Real 'Imitation Game' - Bletchley Park in The Second World War”
On 23rd August 2017 Dr David Kenyon, the British archaeologist and military historian, held a talk for the Deutsch- Britische Gesellschaft about the truth story behind the American film 'The Imitation Game', released in 2014, which focuses on the British codebreaker Alan Turing and his work at the secret British espionage facility at Bletchley Park, north of London during the Second World War. The content of this talk is briefly summarised here.
First, the audience heard about the beginnings of the Government Code and Cypher School (GC&CS) and how until the late 1930s German traffic was not particularly interesting for the codebreakers since Germany was not seen as a strategic threat to UK security.
Bletchley Park was home to the GC&CS which was part of the Secret Intelligence Service (SIS, also known as MI6) from 1939. At first, the country house with and its estate was staffed with 180 personnel. Located outside London but close to the main telephone lines to the city and to the Oxford/Cambridge railway line, Bletchley Park was a perfect fit for their secret activities. The staff number grew fiftyfold in just five years, numbering almost 9,000 people by 1945.
An important part of Bletchley Park history is the Enigma cypher machine, which was used by the Germans from 1927. Dr Kenyon revealed to the audience that there are two main kinds of encryption, code and cypher. While coding involves the replacement of whole words or even phrases by codes or numbers, encipherment involves substituting individual letters with other letters. The enigma machine worked as a cypher method, whereby if the user pressed a letter on the machine another letter would be shown by a light – but not always the same one. Three rotors inside the machine would change the output after each letter, leading to over 17,000 different encryptions. The German bodies used a further manual complication: The user would choose a letter and connect it with another letter through 10 cables in the front of the machine, meaning that there was an additional step of encryption even before the information passed through to the rotors inside the machine. The complexity of encryption was thereby increased to 1023 (103,325,660,891,587,134,000,000) possible encryption options. Since this was quite a high level of encryption for the time, the Germans felt very safe.
Understanding how the Enigma machine worked was a task Polish, French and British secret services had figured out before World War II, but it did not mean they were able to decipher the messages encrypted through Enigma. In 1939 the Poles launched a secret meeting to share all information each service had collected about Enigma. Delegates of all three decryption services met in the Pyry forest close to Warsaw, where the Poles revealed they had already broken the Enigma code. This discovery was the key breakthrough for GC&CS, which started its work at Bletchley Park shortly after the secret meeting.
The two key figures involved in breaking the Enigma code at Bletchley Park were Dilly Knox and Alan Turing. Dilly Knox worked at Bletchley Park from 1939 until his death in 1943. He served as Chief Cryptographer and initiated the first break by GC&CS into the German Enigma code in 1940. Alan Turing was recruited in 1938 and started to work on the design of the Bombe machine, a crucial step in decrypting the Enigma signals. In August 1940, they finished developing the first functioning Bombe machine, which allowed routine decryption for the first time. By the end of the war, 200 Bombe machines had been produced in the UK and another 100 in the US. The system behind the machine was to look at a message in which it was believed the content was already known and then comparing letter relationships until the logic was deciphered. The film shows the message used for this was “Heil Hitler”, but in reality the weather report which came up repeatedly in German communication was a much more common ‘Crib’.
There were some points in history where the Germans had their suspicions that the Enigma cipher may have been broken, but ultimately GC&CS’s breakthrough was never discovered. German mathematicians were certain that the system was mathematically unbreakable, but in fact since people operated the Enigma machines there was certain predictable behaviour which enabled decrypting. The German authorities meanwhile assumed that human leaks were responsible for successes in British intelligence.
Huge quantities of information were processed and archived at Bletchley Park. Large numbers of the staff performed very dull and boring tasks, mostly without even knowing what exactly it was for. GC&CS brought some cultural life to the town of Bletchley though, since drama and other events were performed in an assembly hall, which was also open for local people. The locals did not know who exactly these almost 10,000 people at Bletchley Park were and rumour had it that the site served as a lunatic asylum. In fact, Bletchley Park was only bombed once during the war, and even then it was by accident. The centre did not catch too much attention as it was quite common in the UK during wartime that the Government would take over a country house and establish a secret site. Moreover, the staff were sworn to secrecy, a promise many of them kept until the end of their lives. Around 300 staff are still alive today and many of them meet annually at Bletchley Park’s veterans’ reunion.
29.08.2017, Deutsch-Britische Gesellschaft