Since the release of the film The Imitation Game, it has been widely asserted that

The cracking of Germany’s Enigma code shortening the war by two to four years and saving an estimated 14 million to 21 million lives.

What is the source of this claim and how widely is this view held among historians?

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    See also: history.stackexchange.com/questions/17464/… Mar 29, 2015 at 19:09
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    @JasonAller: A very different question.
    – orome
    Mar 29, 2015 at 19:11
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    – MCW
    Mar 29, 2015 at 20:12
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    @raxacoricofallapatorius Cochise explained why Enigma was not important enough to have a huge effect on the war, which it must have had if the claims here were true. If you can't see the relevance in that, I don't know what to tell you.
    – Semaphore
    Mar 29, 2015 at 22:37
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    This is a question of the type "what if...". Such questions do not belong to history but to the "alternative history". There cannot be any well-justified answer on such a question in principle.
    – Alex
    Mar 30, 2015 at 2:03

3 Answers 3


The very breaking of Enigma - by Turing et al using Bombe and also by pinching of the German Naval codebooks - gave the British a blind spot that did nearly cost them the war. That blind spot was that German Naval Intelligence had broken the British Merchant Marine codes in 1938-9 and was reading transmissions using that code into 1944. The British never suspected, and never changed the code.

When times became particularly tough for the UK in Winter-Spring-Summer of 1942, their focus on fighting the U-boat through Enigma, either using Bombe or pinched codebooks, most likely distracted them from thoroughly investigating why the U-boats were so successful in locating convoys. Yes, the UK was in dire straits through mid-1942, but breaking the German codes was not the only way to fight that battle - changing their own codes would have been sufficient, and was an avenue still available even without Bletchley Park's achievements.

So in the final analysis, the achievements of Bletchley Park were only one of two clear paths to success in the U-Boat war; that war could still have been won without it - whether it would have cannot be said.

If the British Isles had been forced into surrender by starvation, it is hard to imagine that a D-Day landing, or defense of the Suez, could have been maintained. The Soviets could have possibly been forced into a peace by exhaustion if the Germans had another million or so men to defend the Eastern Front, as it is well known that they were running short of manpower by 1945.

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    Could you cite evidence for the causal link between the success in breaking the Enigma and the "blind spot"?
    – orome
    Mar 30, 2015 at 15:07
  • @Pieter Geerkens The point you're missing there is that ships were not transmitting their position all the time: what would the point? The Germans conducted air reconnaissance and wolfpack tactics to detect ennemy convoys and concentrate subs on them. The Allies used gonio to detect concentrations of U Boote and react, and the question was more about having the means to fight the U Boot (asdic, asm grenade launchers....) rather than approximately locating them with Enigma cracking or gonio Jul 2, 2021 at 12:58
  • @totalMongot: 1) What is your point? 2) How is it relevant to my answer or the question? The Germans knew the details - including composition and departure date - for British convoys as a consequence of breaking the British marine codes. Jul 2, 2021 at 13:05
  • @PieterGeerkens 1/ The point is that you give two reasons for the defeat/shortening of the war: breaking enigma versus the possibility to change marine codes. 2/ It is to relevant to highlight that all these causes are few in front of the "hunter-killer" tactic 3/ So there is no shortening nor lengthening Jul 2, 2021 at 13:21

As Andrew Hodges, the author of the authoritative Turing biography The Enigma reports, "the main serious source for this type of claim comes from a talk given at Cambridge in 1993 by Sir Harry Hinsley, the official historian of British Intelligence in WW2":

Now the question remains how much did it shorten the war, leaving aside the contribution made to the campaigns in the Far East on which the necessary work hasn't been done yet. My own conclusion is that it shortened the war by not less that two years and probably by four years - that is the war in the Atlantic, the Mediterranean and Europe.

His argument is worth reading in full, but is based on several lines of reasoning but begin with turning, in North African an "almost certain defeat into a stalemate", keeping Rommel "out of Egypt between his victory at the Battle of Gazala in 1942 and the British getting ready for their own victory at El Alamein" chiefly by "killing off his seaborne supplies" without which success, the Allies would have abandoned the operation against North West Africa, resulting wither in delays of at least a year of other crucial strategic efforts — notably the Normandy landings. Further these landings themselves could not have been conducted at the scale and with the success they were, without the successes at Bletchley Park, and to the extent that the Allies "wouldn't in fact have been able to do the Normandy Landings, even if [they] had left the Mediterranean aside, until at the earliest 1946, probably a bit later."

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    However the claim that the African campaign had its seaborne supplies cut off thanks to breaking the Enigma code should be taken with caution: first, the italian were also broken and they were not based on Enigma, and second in the little Mediterranean Sea, the question was not to be able to locate the convoys, but to be able to attack them: Malta was the base for Allied (mainly British) sea and air forces attacking the convoys, and keeping Malta out of water was a matter of convoys breaking with bruteforce their path to the island against air and naval forces rather than an intelligence war Jun 6, 2019 at 21:08
  • @totalMongot The question is: what is the source.
    – orome
    Jun 6, 2019 at 22:32
  • Oh sorry, as I am not a native speaker, I did not understand that. I understood it as "on what basis/facts does the claim stand" Jun 7, 2019 at 16:42

The premise of the question is incorrect, in that the Enigma was never "cracked". If you read "The Hut Six Story" by Gordon Welchman, you will find that Enigma messages could only be translated when operators made errors such as using the same key repeatedly or repeated use of the same base codes ("discriminants"). When the Enigma was used correctly it was unbreakable.

Nevertheless, many transmissions were intercepted and decrypted due to improper operational use of the machine.

The estimate of lives saved is based on the idea that the project shortened the war by "two to four" years, thus extrapolating that 2 years times 7 million deaths per year is 14 million. The origin of the "two to four" years idea I think is the 1974 book "The Ultra Secret" by Winterbotham.

While cryptography operations were certainly helpful, claiming that it shortened the war by two years is an overstatement. For example, in the Battle of Atlantic, the theater in which the decryptions were supposedly most important, I doubt anyone would characterize code breaking as the decisive technology. Radar, direction finding, convoy tactics, sonar, and anti-submarine aerial patrols, especially from Iceland, were all probably more important to the outcome than code breaking.

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    Read One Day in August for the most up-to-date interpretation of the significance of the Enigma. Mar 30, 2015 at 1:06
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    @PieterGeerkens Why are you posting this as a comment on my answer? Mar 30, 2015 at 1:07
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    Because it describes the importance of pinched codebooks in reading the Enigma code, even when properly used. This was how the Brits read German coded transmission in real-time, through most of 1941 and again from late 1942 onwards. Even when Turing's Bombe worked, it was very slow. Mar 30, 2015 at 1:20
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    @PieterGeerkens What does this have to do with answer? Put it in your own answer or maybe a comment to the question. This has nothing to do with my answer. Mar 30, 2015 at 1:40
  • @TylerDurden: How do you arrive at the conclusion that "the Enigma was never 'cracked'"; specifically that "when the Enigma was used correctly it was unbreakable"? This is certainly wrong..
    – orome
    Mar 30, 2015 at 16:09

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