By early 1944, the Allies, under the leadership of U.S. general Dwight D. Eisenhower, had been planning an invasion of France for more than a year. The Germans, anticipating such an invasion since 1942, had begun building the Atlantic Wall, a series of heavily armed fortifications all along the French coast. As the Allied invasion plan became more specific, it was dubbed Operation Overlord, and preparations and training for the mission began in earnest.
As part of the invasion plan, the Allies instigated a mass disinformation campaign in hopes of directing German forces away from the actual landing point. As part of this effort, the Allies made use of German spies in Britain who had been turned and were serving as double agents. These double agents helped convince the German leadership that the invasion would take place near Calais, the point where the English Channel was narrowest, when in fact the invasion was targeted farther south, in Normandy.
The invasion was launched early in the morning of June 6, 1944—the famous D-Day—barely a day after U.S. troops had liberated the Italian capital of Rome. Overnight, roughly 20,000 British and American airborne troops had been dropped by parachute and glider a short distance inland of the Normandy coast, ordered to do as much damage as possible to the German fortified coastal defenses. Meanwhile, over 6,000 ships were making their way across the English Channel to deliver a huge expeditionary force onto five separate beaches between Cherbourg and Caen. The first wave alone brought 150,000 Allied soldiers to the French shore, and over the coming weeks, more than 2 million more would enter France via the Normandy beaches—to this day the largest seaborne invasion in history. Opposing the invaders were thousands of German troops manning the fortifications above the beaches.
The first day of the invasion was costly for the Allies in terms of casualties—especially at one landing point, Omaha Beach—but the Germans were vastly outnumbered and rapidly overwhelmed by the incoming forces. The German high command still believed that a larger invasion was imminent at Calais or elsewhere, so they withheld reserve forces in the area from moving against the Normandy invaders. The Allies therefore accomplished nearly all of their set objectives for the first day, which included fully securing the landing areas.
Breaking out of the Normandy coast and into inland France proved more difficult, in part because of stubbornly defended German defense posts at Cherbourg and Caen, which framed the area. The Allies were unable to advance inland in significant numbers until July 28, 1944, by which time the two German forts had been defeated. During August, the Allied forces that continued to land in Normandy were able to move rapidly into the heart of France.
On August 15, a second Allied assault was made into France, this time along the Mediterranean coast in the south. This campaign, called Operation Dragoon, involved nearly 100,000 troops, who rapidly spread out northward into France. With this southern operation a success, Allied forces were able to approach the French capital from two directions.