The Allied invasion of western Europe, launched on June 6, 1944, was the implementation of Operation Overlord (and the phase of Overlord devoted specifically to the initial assault, Operation Neptune), the product of some two years of planning, training, and buildup of personnel, equipment, and supplies.

By May 1944, 47 divisions%u2014about 800,000 combat troops%u2014had been assembled at embarkation points in Britain, ready to cross the English Channel to designated beaches in Normandy, France. The operation was under the overall command of U.S. general Dwight David Eisenhower, supreme Allied commander, Europe, whose headquarters was designated Supreme Headquarters, Allied Expeditionary Forces (SHAEF). Directly under Eisenhower was British general Bernard Law Montgomery, who had field command of all Allied ground forces.

The Allies had chosen to land along a 50-mile expanse of Norman coast, from Caen west to the base of the Cotentin Peninsula. Tactically, this area was divided into five beaches, code-named, from east to west, Sword (to be assaulted by the British 3rd Division), Juno (Canadian 3rd Division), Gold (British 50th Division), Omaha (U.S. 1st Division and part of the 29th), and Utah (U.S. 4th Division). These initial landings represented about 156,000 troops.