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
They avoided using too much of the information, carefully restricted who could access it, and created various ruses to make it appear that they had alternative sources of intelligence. None of this was new or unique to the Second World War: it’s standard spycraft stuff.
A similar issue comes up in counterintelligence: if you have convinced an enemy spy to turn traitor, how do you stop your enemy from realising that they have suddenly stopped getting useful information from them? Well, you continue to allow them to send some information, but remove some of the detail or ensure it arrives a bit too late to be useful. Then you can mix in some fake information that will actively hurt the enemy (e.g. by suggesting that you are about to launch an attack in one location, when you are actually planning an attack somewhere completely different).
Of course, your enemy will be aware of all these possibilities and will be careful to obscure their own knowledge, so you will never be completely certain whether they suspect something is up.
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Adding to what others have said, the actual investigative abilities of the germans was pretty poor. The Gestapo while very feared, were essentially beaurocrats filtering through denunciations and heavily reliant on people denouncing each other.
The actual German military intelligence, the Abwher, was run by Admiral Canaris, who very much hated the Nazis and may or may not have been a British spy.
For some uses in meshed with multiple other sources (eg u-boats were reported by agents, sighting by aircraft and ships, HF/DF), so it was one element among many and not the most obvious. In other uses the information was more of strategic value than tactical, so informed senior leadership decisions in ways that were not obvious to the Germans.
They took care to ensure tactical information was not compromised. As an example – Enigma intercepts told when Italian convoys to Africa would depart and what route. So reconnaissance planes would be tasked to fly over the area (as well as other areas of course). Convoy reports being spotted, RAF and RN show up and wreak havoc, hit explained. In one case when no planes were available they decided to hit the convoy anyway, then transmitted a signal to Agent 99 in Naples – “Congrats on accurate convoy info. 2,000 Fr in Swiss account”, knowing that this cipher had been broken by the Germans. Hit explained and as a bonus Germans disrupt Naples docks for weeks trying to find Agent 99.
This question reminds me of a story of Afghanistan after 9/11. Osama bin Laden was putting out videos, and at one point an American geologist recognized the rock Osama was standing in front of. It was a particular type of stone only found in one part of the country — in other words, he knew where Osama was filming the videos.
So he contacts the U.S. government and lets them know. The military was all “Awesome! We’ll be able to catch him!”
The dude is so happy his very specialized knowledge was so useful that he did what any red blooded American in that situation would do: he *bragged about it on the Internet*.
Thousands of Intel experts cried out in anguish, the fell silent (again).
The next video from bin Laden, he’s standing in front of a tarp, because apparently the Taliban has Internet access.
We were able to keep the secret in WWII because there was no Internet, and people weren’t self-aggrandizing morons.
This exact question was included in the movie the imitation game. What they portrayed was that some messages must be “missed” thus some allies will have to die.
They called the intelligence Ultra, like “ultra secret”, above even “top secret”.
https://en.wikipedia.org/wiki/Ultra_(cryptography)
It wasn’t allowed to be left unattended. Once read by officers in the field, it was burned. The entire programme was secret.
The rest of the operation relied on deception… fake spies, sending planes to “scout” areas the Allies already knew about from Enigma before attacking, turning Nazi spies and using them to report back.
While collecting the intelligence relied mostly on mathematicians and computer scientists, “safe” use of the intelligence was mostly psychological operation.
As others have stated, if they used every piece of info they received to make decisions, the Nazis would have caught on quickly. Basically, they had to only act on the most vital information and act such that it appears the information could’ve been gathered differently or the response to an attack, for example, was just a coincidence.
If you’re interested, there’s a whole scene in the movie The Imitation Game where the characters argue about this. Essentially the discussion was: “Sure, we could do a lot if we crack the code, but if we do too much, it’ll be obvious and they’ll change how the code works. We have to be careful how we use the information, even if lives are at stake, for the greater war effort and to save more lives.”
You should read Cryptonomicon by Neal Stephenson, or listen to the audiobook. It’s a fantastic novel that is all about this.
The British using misinformation to conceal crucial military secretes is nothing new in fact it’s partly where the “carrots are good for your night vision” idea comes from— the Brit’s claimed that they were feeding their pilots extra carrots because it improved their vision and made them better able to “find” German bombers during the blitz, when in reality they had developed an advanced radar system…. And in another case had been intercepting German naval transmissions and intercepting the ships and lied and said they had developed a sensor system that could detect [something] (I can’t remember the details) and the Germans believed the lie so they “solved” the problem by developing a radar absorbing paint to prevent detection by the sensor system (that didn’t actually exist)…
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