How did they get over the catch-22 that if they used the information that Nazis could guess it came from breaking the code but if they didn’t use the information there was no point in having it.
EDIT. I tagged this as mathematics because the movie suggests the use of mathematics, but does not explain how you use mathematics to do it (it’s a movie!). I am wondering for example if they made a slight tweak to random search patterns so that they still looked random but “coincidentally” found what we already knew was there. It would be extremely hard to detect the difference between a genuinely random pattern and then almost genuinely random pattern.
In: Mathematics
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Partly by coming up with reasonable explanations for how they were finding things out. For example, when attacking axis vessels at sea they might send out a plane to “discover” the vessels’ location. The axis vessels would report they had been spotted by a plane, then attacked. The axis also mistakenly attributed at least some of the allied success at U-boat hunting to HFDF (high frequency direction finding), i.e. listening for U-boat radio transmissions to pinpoint their location.
They calculated how many successful intel interceptions could be interpreted as dumb luck or intel gathered by other means (e.g. sending scouts ahead even if they knew enemy positions), and rationed them out for really important missions.
They also had double agents who fed Nazis false information on intelligence available to Allies and how they viewed their success rates.
a) claiming other sources like spies
a) not using all the information from it, focusing on the big impact full decisions. This might mean even letting a few people die, to save more in the long term.
You do use the information, but you have to be very clever about when you are using it. For example, you might decide to use it non-optimally in some cases where it can be confused for a plausible coincidence. Imagine you have decoded that there is going to be a bombing of CITY on DATE. For some reason, high command has decided that this needs to be defended against. Military planners now need to come up with a plausible excuse for why CITY *just happened to have* some form of air defense that it would not otherwise have. But you also can’t make it too obvious. So maybe you divert a fraction of one of your armies in the region to temporarily be stationed there during DATE. You can’t divert the entire army without being obvious about it, but surely they can spare some anti-air capable machinery.
Depending on how secure(/paranoid) you want to be about the ruse, you can feed some fake documents/orders about the diverted forces complete with fake reasons to operatives that you are *pretty sure* are Nazi spies (top tip; don’t automatically arrest someone if you know they are a spy). Figuring this stuff out is essentially the day job of military intelligence.
You cannot use your decoded information *constantly* though. High command and military intelligence will need to coordinate/plan/decide what information is important enough to act on, what is irrelevant enough not to act on (irrelevant in the terms of the greater war), and what information is important enough to act on with such force it is obvious you have a decoder.
edit; there are far more fun things you can do. You can simply lie about having some form of new radar tech. Or you pretend that eating carrots has improved your pilot’s eyesight to justify your better intelligence. One of the ‘fun’ things about war is that there is chaos on all sides. Your excuses don’t have to be perfect because your opponent does not have the time and resources to verify everything anyway. Everyone on all sides is working with incomplete and often unverified and/or vague data. Your excuses only need to be *plausible*.
There’s a good book called [Bodyguard of Lies ](https://en.wikipedia.org/wiki/Bodyguard_of_Lies)that covers WW2 from an intelligence perspective. To summarize, they knew very well that if the fascists figured out Engima was comprised that they’d change to a different system.
So, they would engineer situations to create plausble alternative explanations. For example, if the Allies had intercepted a transmission that a very valuable cargo ship was to leave port on to-morrow at 8 AM, they’d arrange for a fly by of an on obsever aircraft that morning, and so forth.
Unfortunately, they could not do it all of the time. At one point, the British knew the Luftwaffe was going to bomb Coventry and realized that if they evactuated the city, it’d give the game away. [They did what they could but had to allow the city to be hit.](https://winstonchurchill.org/resources/myths/coventry-what-really-happened/)
They did use the information; they just had to be careful with it and use it to help win the war in the bigger picture.
In any situation where it seemed like the Allies were aware of their plans, the Nazis generally thought that there would have been an information leak elsewhere. There was almost always an alternative explanation. They ultimately believed that Enigma was unbreakable and never stopped to think that it could have been broken.
It’s also important to know that the operations at Bletchley Park were highly secretive. Only the highest echelons of the British forces and government were aware of it. There was almost no Axis spy network in Britain, so there was no way for them to find out that Engima had been broken outside of conflict.
In the book Double Cross (not the Patterson book) the author explains how they allowed certain non crucial plans to be executed by the enemy so they had a false sense of confidence in the security of their communications. The complexity and depth of the spy game in WW2 is actually really amazing. The allies had their enemies thoroughly infiltrated and the axis spy game was weak af. Despite being allies (at a certain point) the Russkies completely infiltrated their own allied intelligence up the highest level. If Germany hadnt turned on Russia their spies might have been able to turn the tide of the war in their favor but probably not even still once the American war machine was in 5th gear.
The information from enigma was never used unless there was some other possible way that the allies could have obtained the information.
It was super secret. Most of the Allies, even at the general level did not know about Enigma. There was also no axis spy network in the UK. They gave intelligence from enigma a new designation “ultra secret ” and then used a codename for that called Boniface.
MI6 created a fake master spy who supposedly ran a spy network across Germany and named him Boniface. Intelligence from cracking enigma was attributed to human intelligence from this network.
Not all the intelligence was directly actionable either, a lot of the most useful intelligence was hearing how little fuel and reinforcements the Axis had so knowing how hard they could push enemy forces.
But mostly the issue was that used correctly enigma is impossible to crack. Germany didn’t really consider it was possible. It wasn’t. It was only possible because of mistakes operators had made, and the capture of some working machines.
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