The invasion of Normandy, which was the largest land and sea attack in history, code-named Operation Overlord. At dawn on this day, British, American, French, and Canadian troops fought their way onto a 60-mile stretch of beach in Normandy. The Germans had dug in with machine guns, rocket launchers, and cannons. They sheltered behind concrete walls three feet thick. Not surprisingly, the Allies took heavy casualties. Despite heavy losses, the Allies held the beachheads. Within a month of D-Day, more than one million additional troops had landed. Then, the Allies punched a hole in the German defenses near Saint-Lo, and the U.S. Third Army broke out.A month later, the Allies marched triumphantly into Paris. By September, they had liberated France, Belgium, and Luxembourg. They then set their sights on Germany.