Operation Overlord, the plan to invade France and push back the Nazi forces, was in development for years, but it couldn't be executed until the time was right. After the Allied forces had destroyed much of Germany's submarine force, they were able to build up a large number of ships in the British isles and make preparations for the invasion.
On June 5, 1944, Allied ships moved into place off the southern coast of France. Among them were hundreds of amphibious landing vehicles filled with 156,000 troops. In the early morning hours of June 6th, Allied bombers began conducting bombing runs on specified targets along the beaches to soften the defenses.
As dawn broke, Operation Neptune was executed and the landing crafts rode up onto the beaches at Normandy, allowing Allied forces to stream out under heavy machine gun fire. The beach was divided into six parts, designated Omaha, Juno, Gold, Utah, and Sword. Three of the parts were taken by American forces, two by British, and the last by Canadians.
Before the landing, a large number of paratroopers had been dropped behind the heavily fortified beach, effectively surrounding the German defenses. Although casualties were high, particularly on Omaha, allied landing forces managed to move forward past mines and obstacles to seize the bunkers and sandbagged machine guns.
Once the beaches were secured, more landing craft arrived to deposit much needed supplies and additional armor. Despite numerous counterattacks by German forces, the Allies were able to fight them off using their newly arrived artillery and armor. By the end of the day, it was obvious that Germany's previously tight grip on France was loosening.
It is estimated that 2,500 Americans were killed in the invasion, along with another 4,000 wounded. An estimated 3,000 British and Canadian troops also died, while the Germans experienced close to 8,000 casualties. The battle was rather costly for the Allies, but absolutely necessary to begin the liberation of France.