When the CCS met at Casablanca in January 1943, it was a time of optimism. The Germans had been decisively defeated in North Africa, though the campaign would continue until May. The Russians had taken the offensive after stopping the Germans at Stalingrad (now Volgograd), and Japanese expansion in the Pacific had definitely been checked. As a consequence, the greatest obstacle blocking offensive operations against the European continent that year was the relative paucity of Allied resources, particularly the shortage of shipping due to the effectiveness of German submarine warfare.
To make the Mediterranean safe for shipping, the Allies at Casablanca decided to invade Sicily after completing the conquest of the North African shore. By seizing Sicily, they hoped also to remove Italy from the war. To increase pressure on Germany, they agreed to initiate intensified air attacks from the United Kingdom, called the combined bomber offensive (Operation Pointblank). But for a major invasion across the Channel in 1943 the Allied leaders judged their resources insufficient. Though they set up a combined command and planning organization, it was designed to plan for small-scale raids and a return to the Continent in 1943 only if the Germans collapsed. A full-scale invasion was reserved for 1944.
Studying the Dieppe experience, the CCS planners concluded that the strength of the enemy defenses along the Channel coast required an immense concentration of power in the initial assault. Instead of dispersed landings, instead of many separate assaults by regimental and Commando units, it was better to make a single main landing. The beachhead initially secured should then be expanded and developed into a lodgment for the entire invasion force scheduled to follow. The area of initial assault and subsequent lodgment had various requirements. It had to be within range of fighter planes based in the United Kingdom; it had to provide airfields and sites suitable for constructing airfields soon after the invasion; it had to have at least one major port; and the landing beaches had to be sheltered from winds, suitable for prolonged maintenance operations, provided with adequate exits, and backed by good road nets. Furthermore, naval shelling, air bombardment, or airborne landings would have to be capable of reducing or crippling the beach defenses. The area most appropriate for initial landings, the planners decided, was the Channel coast of France between Caen and Cherbourg.
When the CCS approved this analysis on March 1, 1943, they transmitted it as the basic paper for cross-Channel planning to Lt. Gen. (later Sir) Frederick E. Morgan, a British officer appointed that month as chief of staff to the supreme Allied commander (COSSAC). In a subsequent directive issued on April 23, the CCS instructed Morgan to set up an Allied headquarters for the supreme commander, who had yet to be named, and to plan to invade northwestern Europe as early as possible in 1944. Meanwhile, in February 1943, General Eisenhower, the supreme Allied commander in the Mediterranean, had relinquished command of ETOUSA, with its headquarters in England, to Lt. Gen. Frank M. Andrews. In May, when Andrews died in an air accident, Lt. Gen. (later Gen.) Jacob L. Devers took his place.
In May 1943, at the Trident Conference in Washington, the CCS enlarged the Allied bomber offensive from the United Kingdom, decided to exploit the projected Sicily operation to ensure the elimination of Italy from the war, and set a target date for a cross-Channel operation on May 1, 1944. In the future, men, materiel, and supplies were not to be diverted from the Bolero buildup for Mediterranean operations; on the contrary, 7 Allied divisions were to return from the Mediterranean area to the United Kingdom. The Allies visualized 29 divisions available for the invasion of France by the spring of 1944.
The reason for this optimistic estimate was the success of Allied warships and planes in destroying a growing number of German submarines during the spring of 1943. The decrease in shipping losses, combined with an increase in shipyard production and the freezing of resources in the Mediterranean, made possible a tremendous buildup of American forces in the United Kingdom. It was predicted that 1,300,000 United States troops (400,000 air force and 900,000 ground combat and service troops, including more than 18 combat divisions) would be in the United Kingdom by May 1944.
During the summer of 1943, COSSAC formulated three plans: Cockade, essentially a deception operation designed to pin German forces down in the west by encouraging their expectations of an Allied invasion that year; Rankin, a blueprint for occupying the Continent in case of a sudden German collapse; and Overlord, an invasion in the Caen-Cotentin area with an initial assault of from 3 to 5 divisions. In reality a concept to be used as the basis for later detailed planning, Overlord accepted the risk of prolonged beach maintenance by depending on the development of two prefabricated ports (code named Mulberries) to be towed across the Channel during the invasion. Under Overlord the initial mission of the invasion forces was to gain a lodgment area between the Seine and Loire rivers in France. As increasing numbers of combat units entered the lodgment area, ports, airfields, and supply installations would be developed and organized to support a subsequent drive toward Germany.
The planners assumed that it would take three months to secure lodgment. They then expected a pause for logistical reasons before an advance could be made beyond the Seine. Because they anticipated that the Germans would destroy the facilities of Cherbourg and Brest, they thought of developing a major port of entry for United States forces on the south shore of Brittany at Quiberon Bay (Operation Chastity).
The Allied conquest of Sicily ( July-August 1943), the fall of Benito Mussolini ( July 25), negotiations for the surrender of Italy (eventually announced on September 8), and preparations for an Allied invasion of the Italian mainland (to be initiated on September 3), together with the Soviet seizure of initiative on the eastern front, provided a bright background for the CCS meeting at Quebec in August 1943. Though the CCS accepted COSSAC’s Overlord concept, the debates between the Allies demonstrated divergent points of view. The British espoused a strategy essentially opportunistic, a view that reemphasized peripheral operations aimed at reducing German power by indirect attack (increased air and sea operations, plus intensified ground operations in the Mediterranean) in order to make the cross-Channel attack a success without question. They favored leaving the timing of Overlord somewhat indefinite. The Americans, wanting a power thrust to be made as quickly as possible, urged a definite commitment for Overlord, preferably May 1. The result was a compromise. Though May 1 remained the target date, it was not an altogether firm commitment. Yet the Allies agreed to give Overlord strict priority over operations in the Mediterranean. Accepting COSSAC’s wish for a diversionary invasion of southern France, the CCS instructed General Eisenhower to draw plans for an operation to be executed from Mediterranean resources, timed to coincide with Overlord, and designed to gain lodgment in the Toulon-Marseille area, with a subsequent exploitation to the north and a juncture with the Overlord forces.