The following excerpts are taken from Alan Moorehead's Eclipse: An Eyewitness Account of the Invasion of Europe first published in 1945, a year after the invasion..
THE CAEN-CHERBOURG BATTLES
[June 6th, the day of the landing, General Jodl ordered from Hitler's headquarters that the Allied bridgehead must be 'cleaned up by midnight.' He was told that this was impossible.]
ROMMEL by the middle of June had taken his decision. Or rather the decision began to be forced on him, partly by his own imperious aggressiveness and partly by the dreams of Hitler. The Allies had won the first 'battle of the beaches.' Well and good. They could still be driven off. They could be contained in the narrow bridgehead. They could be continually harassed and attacked. Then at the first sign of weakness the panzers would make their drive through to the sea. The battle of France was going to be fought in Normandy. And the order was: 'Attack. Keep on attacking.'
It was a policy the end of which no one could see, a bull-at-a-gate policy, a short range policy, a gambler's policy that might eventually suck up every German reserve in France. And it was the policy which we could most nearly have wished for. There were still two strong German armies in northern France; the Fifteenth, north of the Seine, and the Seventh, grouped round the bridgehead. In addition there were still the forces in the south. Even at this early date the Germans decided to abandon southern France. All troops down there which were capable of movement were directed northward on to the bridgehead. At the same time several panzer divisions were brought across from Russia, and Rommel began to milk the Fifteenth Army. Bit by bit the reinforcements were brought up to the line in Normandy and out directly into battle. A series of chiselling attacks were developed along the line; principally around Caen.
This is the point at which the flying bomb enters the story. The launching sites were established north of the Seine, largely in the area between Amiens and Dunkirk. They were designed to destroy London. It was also hoped that they would break up the invasion by smashing the embarkation ports in southern England. But the programme for the flying bomb was much delayed. First there had been the fantastically lucky and successful raid by the RAF on the experimental station at Peenemunde, when so many of the German scientists had been killed. Then when some two hundred launching sites had been established the RAF had blotted them out. The opening barrage of flying bombs, which was planned for the autumn of 1943, was only ready to come operation on a limited scale in the summer of 1944: nine months late.
With some reason Germany placed tremendous hopes in the flying bomb. Vast underground factories were at work. There was a reasonable chance that by October 1944 they would be able to increase by five times the number of missiles in their original barrage. One can imagine that Rommel was therefore instructed with some urgency that the launching sites north of the Seine were to be protected at all costs. It was reasonable to suppose that the Allies might attempt another landing in the Calais area in order to silence the flying bomb. How far then could Rommel milk the Calais garrison, the Fifteenth Army, in order to reinforce his troops in Normandy? He needed the troops badly at the bridgehead. He was running round the outside of a perimeter, while the Allies sat compactly inside. Given the whole of the Fifteenth Army he might smash the invasion, or at least contain it until the rains came and he had thrown up a defensive line. But could he take the risk of entirely denuding the flying bomb sites of their garrison?
In the end it was a compromise. He took divisions away from the Fifteenth Army one by one. As the German position round the bridgehead became more and more critical he accelerated the process. At length only a skeleton army remained north of the Seine. Some forty divisions were committed to the Normandy battle, and when they were outmaneuvered and beaten there was nothing left in all France; not even enough men to defend the flying bomb sites for a few weeks.
The whole battle of Normandy becomes clear if this point is understood; the fact that one by one the German divisions were lured on to the Allied lines round the bridgehead, and there cut up one by one. Had they all been committed together the Allies might well have been contained in Normandy for another six months or a year. It might have been another, larger Anzio. Alternatively, had Rommel abandoned the Normandy battle in June, and withdrawn his forces to stand on the Seine or even back on the Rhine, the war might have been still further prolonged. As it was, he suited our purposes perfectly. ...