Operation Overlord also called Normandy Invasion, or D-Day, during World War II, the Allied invasion of western Europe, which was launched on June 6, 1944 (the most celebrated D-Day of the war), with the simultaneous landing of U.S., British, and Canadian forces on five separate beachheads in Normandy, France. By the end of August 1944, all of northern France was liberated, and the invading forces reorganized for the drive into Germany, where they would eventually meet with Soviet forces advancing from the east to bring an end to the Nazi Reich.
Planning, 1941–43: Hitler’s Reich, east and west
In midsummer 1943, a year before the Anglo-American invasion of Normandy that would lead to the liberation of western Europe, Adolf Hitler’s Wehrmacht (“Armed Forces”) still occupied all the territory it had gained in the blitzkrieg campaigns of 1939–41 and most of its Russian conquests of 1941–42. It also retained its foothold on the coast of North Africa, acquired when it had gone to the aid of its Italian ally in 1941. The Russian counteroffensives at the Battle of Stalingrad and the Battle of Kursk had pushed back the perimeter of Hitler’s Europe in the east. Yet he or his allies still controlled the whole of mainland Europe, except for neutral Spain, Portugal, Switzerland, and Sweden. The Nazi war economy, though overshadowed by the growing power of America’s, outmatched both that of Britain and that of the Soviet Union except in the key areas of tank and aircraft production. Without direct intervention by the western Allies on the Continent—an intervention that would center on the commitment of a large American army—Hitler could count on prolonging his military dominance for years to come.
The second front
Since 1942, Soviet leader Joseph Stalin had been pressing his allies, U.S. President Franklin D. Roosevelt and British Prime Minister Winston Churchill, to mount a second front in the west. It was impossible in the circumstances. America’s army was still forming, while the landing craft necessary to bring such an army across the English Channel had not yet been built. Nevertheless, Britain had begun to prepare theoretical plans for a return to the continental mainland soon after the retreat from Dunkirk, France, in 1940, and the Americans, immediately after Hitler declared war on the United States on December 11, 1941, had started to frame their own timetable. Less inhibited than the British by perceived technical difficulties, the Americans pressed from the start for an early invasion—desirably in 1943, perhaps even in 1942. To that end, George C. Marshall, Roosevelt’s chief of staff, appointed a protégé, Dwight D. Eisenhower, to the U.S. Army’s war plans division in December 1941 and commissioned him to design an operational scheme for Allied victory.
Operations Roundup and Sledgehammer
Swiftly convincing himself that the priority of “Germany first” agreed to by Roosevelt and Churchill in the Atlantic Charter was correct, Eisenhower framed proposals for a 1943 invasion (Operation Roundup) and another for 1942 (Operation Sledgehammer) in the event of a Russian collapse or a sudden weakening of Germany’s position. Both plans were presented to the British in London in April 1942, and Roundup was adopted. The British, nevertheless, reserved objective doubts, and at subsequent Anglo-American conferences—in Washington in June, in London in July—they first quashed all thought of Sledgehammer and then succeeded in persuading the Americans to agree to a North African landing as the principal operation of 1942. Operation Torch, as the landing in North Africa, was to be code-named, effectively postponed Roundup again, while subsequent operations in Sicily and the Italian mainland delayed preparations for the cross-Channel invasion through 1943 as well. The postponements were a principal cause of concern at inter-Allied conferences at Washington (code-named Trident, May 1943), Quebec (Quadrant, August 1943), Cairo (Sextant, November 1943), and Tehrān (Eureka, November–December 1943). At the last gathering, Roosevelt and Stalin combined against Churchill to insist on the adoption of May 1944 as an unalterable date for the invasion. In return, Stalin agreed to mount a simultaneous offensive in eastern Europe and to join in the war against Japan once Germany had been defeated.
The decision taken at Tehrān was a final indication of American determination to stage the cross-Channel invasion; it was also a defeat for Alan Brooke, Churchill’s chief of staff and the principal opponent of premature action. Yet despite Brooke’s procrastination, the British had in fact been proceeding with structural plans, coordinated by Lieutenant General Frederick Morgan, who had been appointed COSSAC (chief of staff to the supreme Allied commander [designate]) at the Anglo-American Casablanca Conference in January 1943. His staff’s first plan for Operation Overlord (as the invasion was henceforth to be known) was for a landing in Normandy between Caen and the Cotentin Peninsula in the strength of three divisions, with two brigades to be air-dropped. Another 11 divisions were to be landed within the first two weeks through two artificial harbors that would be towed across the Channel. Once a foothold had been established, a force of a hundred divisions, the majority shipped directly from the United States, were to be assembled in France for a final assault on Germany. In January 1944 Eisenhower became supreme Allied commander, and the COSSAC staff was redesignated SHAEF (Supreme Headquarters Allied Expeditionary Force).