What did the Allies do in order to mislead Hitler and keep the plan a secret?

Since Allied code-breakers had been successful in deciphering Germany's secret communications, they knew that the Nazis had fallen for the deception as D-Day approached. In the weeks leading up to the invasion, the Allies stepped up their aerial attacks on Pas de Calais to throw the Nazis off the scent.

The Allied intelligence services had helped keep the invasion site a secret by a massive disinformation campaign. They misled the Germans with fake army camps, filled with inflatable trucks and tanks, supported with dummy warships.

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