Deception

In World War 2, British undercover security service MI5 devised a clever tactic called XX(Double Cross). Name itself is pretty ironic since this system used captured or self-exposed Nazi German agents against Germany, in a word counter-intelligence.  Thanks to this system London was saved from getting bombed. Germans thought they were bombing coordinates German agents broad casted, thinking they were bombing London but they were bombing nothing the whole war, never correcting their aim.