Upvote:5
Norman Friedman claimed in Fifty-Year War: Conflict and Strategy in the Cold War that Ronald Reagan pretended to be slightly mad as US President to intimidate and unsettle the leadership of the USSR. I am not fully convinced.
On the sneaky stuff by the British, this kind of thing was attempted on a small scale during the operation of the WWII Double-Cross System. It was realised that German attempts to send agents to the UK looked suspiciously successful, from the German point of view. Most of the agents they sent got established and started sending useful information. The success rate was implausibly high.
What was actually happening was that the agents were all being caught and either doubled or impersonated. The Germans were notifying one of their agents in the UK about them, unaware that he'd been one of the first to be doubled, which allowed for considerable certainty about this. As an experiment, the next agent sent was impersonated in a conspicuously clumsy and heavy-handed manner. The Abwehr didn't notice. Source: Hesketh, Operation Fortitude.
Upvote:5
Acting on intelligence obtained via code breaking or spies will alert the enemy and cause them to fix the flaw losing that valuable intelligence source. As much as possible, the western Allies in WW2 made sure that before they acted on any intelligence obtained via code breaking they had to give the enemy some other plausible explaination.
For example, if the location of an enemy ship or convoy was discovered via code breaking the Allies would send out a recon aircraft to conspicuously overfly the target. Only after a plausible period of time after the "sighting" would an attack come. Similarly, the Allies would "let slip" they had spies at enemy ports to explain their uncanny ability to find convoys. This was done particularly in the Mediterranean when attacking vital Axis convoys between Italy and North Africa.
To avoid raising suspicion by sinking every enemy ship, some known targets would have to be let go.
A famous example when this rule was not followed was the brazen shooting down of Admiral Yamamoto's flight by the US. The Americans had obtained details of his flight plans via , their code breaking of Japanese codes. No explanation was offered for how 16 P-38s just happened to intercept the admiral's flight deep in enemy territory. Fortunately for the US, the Japanese did not suspect their codes were broken.
Computer security uses "honeypots" to catch attackers. A honeypot is a system which seems legit but is all fake. Its purpose is to divert attackers from the real systems and leave them thinking they have made a real break-in. Honeypots are carefully monitored for break-ins which are then analyzed to harden the real systems and catch the attackers.