The British, evicted from Europe in the spring of 1940, vowed to return but it was clear that they could not do so alone, nor, they felt, could an invasion of Nazi-held mainland Europe take place for several years and until Germany had been severely weakened by attacks elsewhere, notably round the periphery of her conquests. In the end, an Allied return to the continent owed much to Soviet pressure on Germany from the east; the bulk of the German army was held on the eastern front. The Allies – chiefly Britain, the United States and Canada but also including elements of the occupied European countries – achieved a return to the continent in June 1944.

The date of the landings was a matter of dispute in the Combined Chiefs of Staff. The Americans, true to their military tradition, advocated an early and direct assault on Europe. They had argued for a diversionary landing in 1942 to draw pressure from the eastern front, where the Germans threatened to force the Soviet Union to surrender. The British Chiefs of Staff held firm against the Joint Chiefs of Staff. Not only did they wish to promote their own traditional indirect strategy, based on the Mediterranean, they felt that a descent on Europe in 1942 would be premature. Command of the surface of the Channel could not then be assured, while the Allies did not have overwhelming supremacy in the skies over the sea and Normandy. American troops in Britain in 1942 were very few and the majority of Britain's own soldiers were occupied mainly in North Africa, Burma and Madagascar. Moreover, the major bottleneck, never satisfactorily cleared throughout the war, was the lack of sufficient landing craft [129–30, 133–4, 144]. Even after the troops had been got ashore, much would depend on Germany's army being stretched by operations elsewhere and its means of reinforcement in Normandy effectively blocked. Moreover, as important as the initial landings was the capability to reinforce and supply the army quickly and steadily over many months. Planning for the great expedition, the assembly of much specialised equipment, the gathering of intelligence, elaborate deception and secrecy schemes, not to mention the training not only of the common soldiery but also numerous specialised units, would take many months. The JCS, somewhat chastened and chagrined after losing the argument over a 1942 invasion, proposed 1943.