D-Day, June 6, 1944, was the date of one of the key battles in the struggle for the liberation of Europe. The Allied landings in Normandy are the largest amphibious operation in history. More than 3 million people took part in it, it was prepared for several years and was kept in the strictest confidence. The Germans knew that an enemy landing was inevitable, but when and where it would take place remained a mystery to Hitler and his generals. For the success of the operation, the element of surprise was vital to the Allies - the opening of a second front preceded the attack on the Third Reich itself and ultimately contributed to the defeat of Hitler.