Did Alan Turing's decryption team develop an statistical analysis algorithm to decide whether to use information from decrypted Enigma messages without risking the Germans to find out that they had broken the code, as depicted in the film The Imitation Game?

I would have thought those decisions were made at a much higher level. Some sources claim that the scene in the movie where they decide not to save the brother of one of the members of the team so that the Germans don't suspect that the code has been broken, is fiction. However, there is a scene later where Turing suggests to Menzies (the head of British secret intelligence) that they could develop a method based on statistical analysis to decide when to use the code, only so that they could win the war, but not too much so that the Germans never find out that the code has been broken. The actual meeting between Turing and Menzies probably did not occur, since Turing did not meet him. But the question remains whether Turing (or any of the codebreakers) ever helped to develop or suggested to develop such a statistical analysis.

Other sources claim that in fact, it was Menzies who came up with Ultra, which was the name given to the system to determine which messages to use. Did Alan Turing, or any of the mathematicians in his team, have anything to do with Ultra? Exactly who were the people (besides Menzies) involved in the development of Ultra?

  • This is asking several things the title differs from the main question
    – mmmmmm
    Feb 11, 2015 at 16:46
  • @Mark I don't think so. If you expand a little I can edit to make it clearer.
    – becko
    Feb 11, 2015 at 19:05
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    From wikipedia and its cites and other books I have read Ultra is the codeword for any intellignce from Enigma decryption - so no statistical stuff here - that was just to break the code. Also Wiki says Ultra codeword was named by Geoffrey Colpoys
    – mmmmmm
    Feb 13, 2015 at 15:04
  • @Mark I read that Menzies did use some sort of statistical analysis (I don't know how sophisticated) to determine which decrypted messages to act upon. This was part of Ultra, but maybe Ultra was bigger than that?
    – becko
    Feb 13, 2015 at 15:10
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    If you're interested in a less fictionalized version of at least some of the events that took place see this series of videos: youtube.com/…
    – slebetman
    May 8, 2015 at 22:53

1 Answer 1


The code cracking team wouldn't actually know the contents of any significant message, except by a huge coincidence.

All encrypted messages were sent over radio and could be listened to and recorded by anyone, including the British. During any one day, all encrypted messages were encrypted with the same code. That meant if the code for one message was cracked, the code for all the messages in the day was cracked.

For cracking codes, you wouldn't choose messages that you would think might be important. You would look at unimportant messages that were likely to be handled less careful. An example were messages containing weather reports, which were not really that secret, and which were sent to some people using not very secure codes, and sent to submarines using the Enigma code. That gave the code crackers messages where the plaintext was known, making it much easier to crack. So a huge number of messages that the code crackers saw decrypted, were trivial weather reports.

Once the code was cracked, all the recorded messages would be decrypted, but that wasn't done by Alan Turing's team.

And to keep the fact secret that messages were decrypted, the British secret service used a lot of clever tricks. Ships whose position were found by decryption were "found" by coincidence by airplanes which just happened to search the areas where they already knew an enemy ship was present. Non-existing spies were sent congratulations and money rewards for delivering information that was actually found by decryption. And so on.

  • 1
    Please provide some references to support your claims. (You've been a visitor long enough to know this already, haven't you?)
    – Oddthinking
    May 6, 2015 at 5:23
  • Also, this doesn't seem to address the question.
    – Sklivvz
    May 6, 2015 at 7:42

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