The Normandy landings, codenamed Operation Neptune, were the landing operations of the Allied invasion of Normandy, in Operation Overlord, during World War II. The landings commenced on Tuesday, 6 June 1944 (D-Day), beginning at 6:30 AM British Double Summer Time (GMT+2). In planning, D-Day was the term used for the day of actual landing, which was dependent on final approval.
The landings were conducted in two phases: an airborne assault landing of 24,000 British, American, Canadian and Free French airborne troops shortly after midnight, and an amphibious landing of Allied infantry and armoured divisions on the coast of France starting at 6:30 AM. There were also decoy operations under the codenames Operation Glimmer and Operation Taxable to distract the German forces from the real landing areas.
Supreme Commander of the Allied expeditionary forces was General Dwight Eisenhower while overall command of ground forces (21st Army Group) was given to General Bernard Montgomery. The operation, planned by a team under Lieutenant-General Frederick Morgan, was the largest amphibious invasion in world history and was executed by land, sea, and air elements under direct British command with over 160,000 troops landing on 6 June 1944. 195,700 Allied naval and merchant navy personnel in over 5,000 ships were involved. The invasion required the transport of soldiers and material from the United Kingdom by troop-laden aircraft and ships, the assault landings, air support, naval interdiction of the English Channel and naval fire-support. The landings took place along a 50-mile (80 km) stretch of the Normandy coast divided into five sectors: Utah, Omaha, Gold, Juno and Sword.
The Allied invasion was detailed in several overlapping operational plans according to the D-Day museum:
"The armed forces used codenames to refer to the planning and execution of specific military operations. Operation Overlord was the codename for the Allied invasion of northwest Europe. The assault phase of Operation Overlord was known as Operation Neptune. Operation Neptune began on D-Day (June 6, 1944) and ended on 30 June 1944. By this time, the Allies had established a firm foothold in Normandy. Operation Overlord also began on D-Day, and continued until Allied forces crossed the River Seine on 19 August 1944."
Just prior to the invasion, General Eisenhower transmitted a now-historic message to all members of the Allied Expeditionary Force. It read, in part, "You are about to embark upon the great crusade, toward which we have striven these many months." In his pocket was a statement, never used, to be read in case the invasion failed.