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Having just watched The Imitation Game, I am curious about the influence of the cracking of Enigma on the outcome of WWII.

Which battles did the information decoded by Enigma influence? Which battles would likely have been lost without the cracking of the code?

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    I think this is going to be a difficult question to answer. Enigma was just one intelligence source that was available to the high command. Due to its classified status and the time it took to produce information, it was more of a strategic tool than a tactical one. Also "influence" is a difficult thing to comparatively measure and evaluate.
    – Steve Bird
    Aug 25 '16 at 5:51
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    The Battle of the North Atlantic was the main one, though I have heard allusions to two convoys through the Mediterranean, one each to Egypt and Malta, that were timed using Enigma to avoid U-Boats. Recall that Enigma intelligence landed only on Churchill's desk; and was passed on only with his approval and only when it could be creditably attributed to other sources. The full story is not yet finished on its significance.
    – Pieter Geerkens
    Aug 25 '16 at 5:56
  • I've always read the decoded Enigma heavily influenced the war in the North African theater, but with the "Rommel myth" exposed, I don't know anymore.
    – Brasidas
    Aug 25 '16 at 11:58
  • Matapan, March 41, but that appears to have been Italian Enigma, which was basically the commercial version without plug-board.
    – Conrad Turner
    Aug 25 '16 at 13:38
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According to "Marching Orders", Enigma had a decisive impact on the (Second) Battle of El Alamein. Montgomery's first attacks were thrown back with heavy loss. Under different circumstances, he (or another commander) might have broken off the attack (as General US Grant did at Cold Harbor, in the Civil War).

But Enigma alerted Montgomery to the fact that Rommel's losses were just as heavy in absolute terms, and twice as heavy in proportional terms (Montgomery outnumbered Rommel by at least two to one), and that Rommel was in "truly terrible shape." So Montgomery continued the assault and destroyed Rommel's army by attrition.

Enigma played a part in later campaigns, in Italy, Normandy, etc., but never as decisively as at El Alamein.

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  • I agree with this. The timing of Operation Husky (while Germany had just fully committed itself to Operation Citadelle in the East) is also very suspicious to me...although I know of no evidence that Great Britain and the Americans knew of the massive battle at the time they decided to launch their assault on Sicily...but the timing did have a major impact on Citadelle resulting in the failure of the offensive and leaving Army Group Center in a dire position in the East.
    – Doctor Zhivago
    Aug 25 '16 at 19:54
  • @user14394: The timing was probably not a coincidence, but everyone almost to Tokyo knew of, and could make a good guess at the timing of, the Kursk Offensive. No ENIGMA needed for that one.
    – Pieter Geerkens
    Aug 25 '16 at 22:36
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    This seems wholly unrealistic as an explanation, and an even simpler one is at hand. dead tanks were and are easily spotted by aircraft on the desert sands, and the allies had near total air superiority over Eastern Egypt at this time. Why would Montgomery need ENIGMA intelligence to tell him what his pilots could readily prove to him.. It is also doubtful that ENIGMA intelligence could have turned around fast enough to meet this need, as it typically took days at least to decipher messages, and time on a battlefield waits for no man.
    – Pieter Geerkens
    Aug 26 '16 at 5:39
  • This explanation also plays too easily into the incorrect stereotype of Montgomery as an overly cautious general , when in fact just the opposite was more accurate - he just had difficulty inspiring subordinates to be as aggressive as he himself liked to be. Market Garden is hardly the brainchild of an overly cautious commander.
    – Pieter Geerkens
    Aug 26 '16 at 5:40
  • I agree with @PieterGeerkens: 2nd El Alamein was from the beginning a battel to be led until exhaustion of the Axis forces, using Malta as a noose on Axis's neck. But the battle of Medenine is a battle where Montgmomery could concentrate his antitank forces and minefields because he knew from Enigma that Rommel was grouping tanks from the West to attack at Medenine
    – totalMongot
    Dec 27 '21 at 16:51
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The most obvious single battle that was influenced by ENIGMA may, ironically, be the (early stages of the) Battle of the Bulge. Hitler's paranoia had finally advanced to such state in 1944 that he was convinced the Allies were eavesdropping on his intelligence; so he insisted that all plans drawn up for that attack NOT use the cracked cypher. It is likely that the Allies had become used to never being grossly surprised, leading to a degree of over confidence that cost lives in December 1944.

Note that even though Hitler's conclusion was correct, this is still really just Hitler's paranoia showing though. The use of ENIGMA intelligence by the Allies was so sparing that he had no logical basis for this conclusion. Other than in the North Atlantic, where the battle was truly existential for the British, it was kept as a reserve to prevent exactly the scenario that occurred Dec. 16, 1944 - a massive German surprise attack in a weakly defended sector.

In the Allied favour the key battle/campaign would be that of the merchant marine convoys in the North Atlantic through the dark days of 1941 and 1942. The British never realized that the Germans had broken the merchant marine codes in the mid 1930's, so it was only with the help of ENIGMA intelligence that sufficient convoys got through to keep Britain afloat as it were.

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    this is still really just Hitler's paranoia Just because you're paranoid doesn't mean they're not after you :-)
    – Matt
    Aug 25 '16 at 6:38
  • I have read the Allies prepared well for the Battle of the Bulge and the undefended sector in the middle was left so intentionally.
    – Anixx
    Aug 25 '16 at 7:46
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    @Anixx: Not by any accounts I have read. What is your source for that account?
    – Pieter Geerkens
    Aug 25 '16 at 10:53
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    You mean battle not ballet, right?
    – Ludi
    Aug 26 '16 at 18:26
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    [i]The use of ENIGMA intelligence by the Allies was so sparing that he had no logical basis for this conclusion[/i] Sooooo.... this means that Enigma was of no use?^
    – totalMongot
    Dec 27 '21 at 16:52
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The D-Day Landings.

The British Security Service (MI5) were operating a number of double-agents in UK territory, pretending to their German controllers that they were still diligently spying on the UK, but actually sending back misinformation. Because Enigma was cracked, MI5 realised that every single message being sent back to the German intelligence service was from these double-agents; this meant that there was no intelligence reaching Germany except that being generated and controlled by MI5.

Armed with this knowledge, they launched Operation Fortitude to deliberately feed controlled disinformation to Germany via the double-agents, misleading them as to the location of the planned D-Day landings. This was so successful that, even after the landings were well underway in Normandy, 15 German army divisions were kept in the Calais region to repel the supposed 'real' invasion there which was supposed to follow the 'diversionary' Normandy invasion. This was quite possibly crucial in allowing enough time for the invading forces to establish a beachhead strong enough to support the continued assault.

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The battle of Medenine, March 6th 1943, was influenced by ENIGMA.

Before this battle started, the situations was as follows:

  • In Souh-East of Tunisia, Montgomery was pushing hard but slowly
  • In the West, Rommel had used the time to defeat American forces
  • Rommel had to group again his forces to stop Montgomery

Now, why had the Germans the use of radio communications? Because phone communications were not that much developed in Tunisia, and French had sabotaged some. => So they used radios and Enigma helped decoding the message

Enigma helped knowing the place of the offensive because Rommel had to tell to dispersed armored units where to meet. This was probably as well a lack of cautiousness from German radio operators.

So Montgomery concentrated antitank guns, minefields and tank reserves and defeat the Germans suffered 50 tank as well as infantry losses.

Without Enigma, the German defeat would have not been that big and losses not that high. Moreover, British tanks would have suffered losses as well and that would have hampered later offensive.

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