By May of that year the war had reached its decisive phase, a phase in which invasion was inevitable. The British had been planning to return to Europe since they were kicked off in 1940. The Russians had been demanding the opening of a second front since the June of 1941, insisting that the Germans could never be beaten without one. And the Americans had been in agreement with the Russians since their entry into the war. Generals George Marshall and Dwight D. Elsenhower had argued forcefully for a second front in 1942 and 1943.

Despite the commitment by the three great allies, and despite intense public pressure, another strategy was followed. In November, 1942, the Allies landed in French North Africa, a long way from any major German forces (not to mention from any German cities). In July of the following year they landed in Sicily, and two months later in southern Italy. These operations ran into heavy German opposition, but they did not put a significant strain on enemy manpower. Nor did they seriously weaken Germany's capacity to make war: indeed, German factories were producing tanks and guns at record rates by the spring of 1944. And their guns and tanks were the best in the world - as well they might be, given the Nazis' ability to draw on the expertise and resources of all Europe. In short, the Allied operations in the Mediterranean during 1942 and 1943 were more important for their political than their military results. They left Hitler with few problems either of production or of manpower.

But Hitler did have one major worry in the Spring of 1944, and that was a single point at which his fighting forces were vulnerable.