“Fortitude” was the codename given to the decoy (or disinformation) mission mounted by the Allies to deceive the Germans about the date and above all the place of the landings. The latter were convinced that the British and American attack would come in the Pas-de-Calais area and it was important not to disillusion them. They therefore had to be made to think that a whole group of armies was present in Kent, opposite the Pas-de-Calais.
To deceive the German observation planes, which their antiaircraft defences did their best to avoid, the local estuaries, creeks and harbours were crammed with dummy landing craft, made out of bits and bobs. A giant oil pumping head for PLUTO (made from papier mâché) was erected near Dover, while large numbers of inflatable rubber tanks were positioned in the fields. Plywood vehicles and guns lined the roadsides. At night, convoys of lorries ‑ always the same ones – drove back and forth across the region. For the benefit of the Germans, a team of technicians maintained constant radio traffic between totally fictitious units.
Fortitude succeeded beyond anyone’s wildest dreams. Long after June 6th, Hitler remained convinced that the Normandy Landings were a diversionary tactic to induce him to move his troops away from the Pas-de-Calais, so that a decisive attack could then be launched there. He therefore kept his best units in readiness there, until the end of July, desperately scanning an empty horizon, while the fate of the war was being decided in Normandy.