German Miscalculations Regarding D-Day
The Germans made many miscalculations regarding the Allies invasion of Normandy on D-Day.
While our plans developed and the build-up of supplies and men in readiness for the operation continued with regularity, we had been studying the possible action which the enemy might take in the expectation of an assault against him mounted from the United Kingdom. In any operation as large as OVERLORD it was palpably impossible to keep from the enemy the fact that we intended, during 1944, to launch an attack against Europe. Where, when, and in what strength the attack would be launched was another matter, and I was not without hope that he would not necessarily appreciate that our target was the Normandy beaches. Indeed we had some reason to believe that the enemy expected numerous attacks from many quarters and was continually uncertain as to the strength of any of them, unable in his own mind to determine or distinguish between a threat which we had no intention of launching, a diversion in strength, or an all-out main assault. Thus, he was stretched to the utmost in every theater.
We thought that to the German High Command an assault upon the Pas-de-Calais would be the obvious operation for the Allies to undertake. Not only was this the shortest sea journey where the maximum air cover would be available, but a lodgement in the Pas-de-Calais would lead the Allies by the shortest road directly to the Ruhr and the heart of Germany. Such an operation would have to be mounted mainly from Southeast England and the Thames area. Concentrated in the Pas-de-Calais was the German Fifteenth Army, which had the capability both of shifting its forces to Normandy prior to the assault if the intended area of the attack were to become known and also of quickly reinforcing the divisions in Normandy, after the assault.
Acting on the assumption that this would be the German estimate we did everything possible to confirm him in his belief. Without departing from the principle that the efficient mounting of the operation remained at all times the first consideration, we took every opportunity of concentrating units destined ultimately for the Normandy beachhead in the east and southeast rather than in the southwest. In this way it was hoped that the enemy, by his observations based on aerial reconnaissance and radio interception, would conclude that the main assault would take place farther to the east than was in fact intended. As a result of these measures, we also felt that had an enemy agent been able to penetrate our formidable security barrier, his observations would have pointed to the same conclusion.
Shipping arrangements were made with the same end in view. Surplus shipping was directed to the Thames Estuary where an enormous concentration was already assembled in preparation for the invasion, while landing craft were moored at Dover, in the Thames, and at certain East Anglian ports.
Further support was afforded by the aerial bombing program. The distribution of bombing effort was so adjusted as to indicate a special interest in the Pas-de-Calais. It was also hoped that the bombing of the V-1 sites would be misinterpreted in our favor. Finally the large and very visible components of the artificial harbors, which were subsequently set up on the Normandy beaches, were anchored in Selsey Bay immediately before the invasion, a point farther east than originally proposed.
After the assault had gone in on 6 June we continued to maintain, for as long as possible, our concentrations in the southeast and our displays of real and dummy shipping, in the hope that the enemy would estimate that the Normandy beachhead was a diversionary assault and that the main and positive blow would fall on the Pas-de-Calais when the diversion had fulfilled its purpose. The German Fifteenth Army remained immobile in the Pas-de-Calais, contained until the latter part of July by what we now know from high-level interrogation was the threat of attack by our forces in the southeast of England. Not until 25 July did the first division of the Fifteenth Army advance westward in a belated and fruitless attempt to reinforce the crumbling Normandy front.
Every precaution was taken against leakage of our true operational intentions against Normandy. The highest degree of secrecy was maintained throughout all military establishments, both British and American, but additional broader measures affecting the general public were necessary as D-day approached.
On 9 February, all civilian travel between Britain and Ireland was suspended to prevent the leakage of information through Dublin, where German agents continued officially to represent their government. On 1 April, also as a result of a request made by me, the British Government imposed a visitors' ban on the coastal areas where our assault was being mounted and extending inland to a depth of 10 miles.
Because even the most friendly diplomats might unintentionally disclose vital information which would ultimately come to the ears of the enemy, the British Government took the further unprecedented step of restricting diplomatic privileges. On 17 April it banned the movement of diplomats or their couriers into and out of the United Kingdom and subjected hitherto immune correspondence to censorship. At my request this ban was maintained until 19 June.
Lastly, it was considered expedient on 25 May to impose an artificial delay of ten days on the forwarding of all American mail to the United States and elsewhere and to deny to American personnel trans-Atlantic telephone, radio, and cable facilities. The mail of all British military personnel due to take part in the Normandy operation had been, even within England itself, subject to strict censorship since April.
Preparatory Operations for D-Day