Why is Alan against preventing the first attack after breaking enigma?
In the scene from The Imitation Game, where they are able to crack engima, Alan convinces his teammates to not prevent the next attack.
He says something like:
Lie to somebody when they are expecting to be lied.
What does the above line mean?
And how is preventing this particular attack riskier than preventing any future attack?
Best Answer
I presume this scene is based on a famous urban legend from WWII, known as the "Coventry dilemma".
The story goes that, in November 1940, Bletchley Park decoded an Enigma-encrypted transmission revealing that a bombing raid on Coventry was planned for the 14th. The dilemma was thus: did the British prevent the raid, and risk revealing to the Germans that they'd cracked the Enigma code, or do nothing and keep the decryption a secret at the cost of hundreds of lives?
Winston Churchill supposedly chose the latter, and let the raid happen. 568 people were killed, and central Coventry was almost totally destroyed, but the Germans were left unaware that the Enigma had been deciphered and Bletchley Park was able to go on intercepting German communications.
This is why Turing is reluctant to act on the information they've learned from having cracked the Enigma code: if they do, the Germans will realise the Enigma has been cracked, and change their encryption method. By doing nothing, and pretending they haven't cracked the code, they are effectively lying to the Germans about how much intelligence they have.
[For the record, there is no evidence that the British actually knew of the Coventry raid in advance. It's merely an urban legend. See Wikipedia's section on the myth for more detail.]
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Did Alan Turing actually break the Enigma code?
As early as 1943 Turing's machines were cracking a staggering total of 84,000 Enigma messages each month - two messages every minute. Turing personally broke the form of Enigma that was used by the U-boats preying on the North Atlantic merchant convoys.Why was it so important that Alan Turing cracked the Enigma code?
Cracking the code This machine was able to use logic to decipher the encrypted messages produced by the Enigma. However, it was human understanding that enabled the real breakthroughs. The Bletchley Park team made educated guesses at certain words the message would contain.How did Alan Turing solve Enigma?
Well, the Enigma wasn't perfect, and contained one flaw which was exploited by Turing in order to solve the code. He did this by building a giant machine called the Bombe, which essentially worked backwards through the Enigma Machine coding process in order to determine how the machine was set each day.How Was Hitler's Enigma Machine Cracked?
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Answer 2
How is preventing this particular attack riskier than preventing any future attack?
The answer is given at 2:05 in the video. If the British suddenly attack the U-boat:
"The Germans will know we have broken Enigma."
"They'll stop all radio communications by mid-day, and they will change the design of Enigma by week-end."
The Germans will quickly realize there was no other way that the British could have learned about the attack. They will realize that the British must have cracked the secret Enigma code.
The Germans would then cease all radio communications, and change Enigma within days. If they do that, the British will lose this incredible military advantage that they have. It could take years before they could crack the upgraded version of Enigma, and there's no guarantee that they actually could crack it. The value of being able to decipher the coded German messages, and thereby having an advantage in every future battle and probably the war, outweighs the value of preventing this one attack. It's tragic but logical.
Answer 3
To add to the other two answers, shortly after this scene in the movie they discuss determining HOW MUCH they can interfere, and how to interfere with German plans, to hide the knowledge that Enigma is broken. The fact that Enigma was broken was kept a secret from almost everyone, with Alan's team leaking out what THEY chose for the army to act on and how to act on it.
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