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Operation Fortitude
Operation Fortitude was the codename for the deception operations used by the Allied forces during World War II in connection with the Normandy landings (Operation Overlord).
It was divided into Fortitude North, a threat to invade Norway, and Fortitude South, designed to induce the Germans to believe that the main invasion of France would occur in the Pas de Calais rather than Normandy.
Fortitude was one of the most successful deception operations of the war and arguably the most important. Both Fortitude North and Fortitude South were related to a wider deception plan called Operation Bodyguard.
http://en.wikipedia.org/wiki/Operation_Fortitude