In January 1944 the Allies also appointed an invasion commander. Bernard Law Montgomery, Rommel's desert opponent in North Africa, was nominated, under Eisenhower, as commander of the ground invasion forces. Walter Bedell Smith, an American, continued as Eisenhower's chief of staff, but his other principal subordinates were British: Air Chief Marshal Arthur Tedder as his deputy, Admiral Bertram Ramsay as naval commander, and Air Chief Marshal Trafford Leigh-Mallory as head of the expeditionary air forces.

Montgomery's first acts were (1) to demand and get five divisions to make the initial landing and (2) to widen the landing area to include the Orne River estuary and the base of the Cotentin Peninsula. As finally constituted, the invasion force was to consist of five infantry divisions--two American, two British, and one Canadian--assigned to beaches code-named, from west to east, Utah, Omaha, Gold, Juno, and Sword. On D-Day (the projected first day of the invasion), two American airborne divisions were to land behind the western end of the assault area and one British at the eastern, while amphibious armour was to swim ashore with the leading waves. The Americans constituted the U.S. 1st Army, under Major General Omar Bradley, the British and Canadians the British 2nd Army, under General Miles Dempsey. The British divisions had been under intensive training since 1942, the American since 1943. Meanwhile, intensive logistic preparations provided, by May 1944, almost 6,500 ships and landing craft, which would land nearly 200,000 vehicles and 600,000 tons of supplies in the first three weeks of the operation.