Answer:
to ready for an invasion, in 1942, Germany began construction on the Atlantic Wall, a 2,400-mile network of bunkers, pillboxes, mines and landing obstacles up and down the French coastline. But without the money and manpower to install a continuous line of defense, the Nazis focused on established ports. From the start, the top candidate for an Allied invasion was believed to be the French port city of Calais, only 20.7 miles across the English Channel from Dover.
As part of Joseph Goebbels’ Nazi propaganda machine, the Germans installed three massive gun batteries along the Calais coast with their 406-mm cannons pointed at Dover. The Nazi’s message was clear—attempt to storm Calais and we will drive you into the sea. Meanwhile, the rest of the French coastline, including the northern beaches of Normandy, was less fiercely defended.