After studying the Overlord concept, Generals Eisenhower and Montgomery concluded that the initial assault needed to be strengthened and yet made on a broadened front. This required additional landing craft, troops, and vehicles, and this in turn led to debate over whether the diversionary invasion on the Mediterranean coast of France, an operation code named Anvil, was really necessary. When the Anzio beachhead in Italy exerted its requirements for shipping, Eisenhower in March 1944 suggested canceling Anvil as an attack simultaneous with Overlord. In accepting the recommendation, the CCS assured SHAEF of the additional landing craft and other materiel needed for a stronger cross-Channel attack, but the complex requirements of assembling the means for the invasion of Europe had made it necessary to change the landing date from May to June. Meanwhile, on February 1, Montgomery, Ramsay, and LeighMallory had drawn the initial joint plan (Neptune) for the invasion. A refinement of the Overlord concept, Neptune was at the same time a directive instructing the subordinate headquarters to plan the assault in greater detail.
As finally completed in the spring of 1944, the invasion plan called for assaults by the United States First and British Second armies. The First Army was to invade the Normandy shore in the Carentan-Isigny area with two corps. Northwest of Carentan the 82d and 101st Airborne divisions were to drop near Ste.-MereEglise in order to assist the 4th Infantry Division of the 7th Corps to land on Utah Beach near Varreville. East of Isigny, in the 5th Corps zone, the 1st Infantry Division with part of the 29th Division was to land over Omaha Beach near Vierville-sur-Mer. Operating in the BayeuxCaen area, the British were to send the 50th Division under the 30th Corps across Gold Beach near Arromanches-les-Bains, the Canadian 3d Division under the 1st Corps across Juno Beach near Courseulles, and the 3d Division, also under the 1st Corps, across Sword Beach near Lionsur-Mer. The 6th Airborne Division was to drop northeast of Caen near the mouth of the Or.ne River to protect the British flank.
The troops making the amphibious landings were to be carried by naval transports to positions 11 miles offshore in the American zone and 7 miles offshore in the British zone. The troops then were to board LCVP’s (landing craft, vehicle and personnel) and LCA’s (landing craft, assault), each craft carrying about 30 men. The small craft were to go in abreast in waves and touch down at regular intervals along the length of the assault beaches. Following them were to be larger craft carrying heavy weapons, guns, tanks, and engineer equipment. Finally, LST’s (landing ships, tank) were to nose onto the beaches and disgorge additional men, equipment, and supplies. Naval fire-support plans emphasized neutralizing enemy positions rather than destroying them. The air forces planned to maintain an umbrella of fighter planes to protect the ground and naval units from German air attacks and also to provide air bombardment to help the ground forces overcome obstacles impeding their progress ashore.
Long before the day of invasion, called D-day, the air forces had begun to play a significant preparatory role. Since 1942, British and American airmen had bombed military targets in German-occupied Europe, but no clear directive or over-all plan had existed before the combined bomber offensive directed by the CCS at Casablanca in January 1943. The targets of this offensive were the German industrial and economic systems and the morale of the German people. The Americans favored daylight precision bombing to destroy critical sectors of German industry. Believing daylight bombing too costly, the British favored night bombardment aimed at destroying entire industrial and military areas. Each operated according to its own doctrine, both concentrating on submarine construction yards, airplane factories, transportation systems, oil plants, and other war industries. In October 1943, attempts were first made to coordinate the bombings from North African and Italian bases with the combined bomber offensive from the United Kingdom.
In April 1944, Eisenhower took control of the strategic air forces and used them in support of Overlord. Though the over-all mission of destroying the German military and economic system remained, the particular mission was to deplete the German Air Force and destroy the facilities serving it, to destroy the German oil industry, and to disrupt rail communications, especially those that might serve the Germans in moving reinforcements to the Overlord lodgment area. Heavy air attacks in May 1944 shifted to bridges over the Seine, Oise, and Meuse rivers, and by June Allied air attacks had weakened the railroad transportation system in France to the point of collapse.