D-Day Planning & Preparation: Development of Overlord

D-day, Developing Overlord

During the period of this staff planning for OVERLORD, I was personally occupied with the Mediterranean campaigns and was not in close touch with the plans evolved for the campaign in Northwest Europe, nor did I during this period know that I would ultimately be connected with the operation. In December, however, I was notified by the Combined Chiefs of Staff that I had been appointed Supreme Commander of the Allied Expeditionary Force and that prior to assuming command in England early in January I was to return briefly to Washington for conferences with General George C. Marshall and the Combined Chiefs.

Prior to leaving my Headquarters in North Africa, I was able early in December 1943 to see a copy of the Outline Plan of OVERLORD and to discuss it with Field Marshal (then General) Sir Bernard L. Montgomery, who was to command 21 Army Group, and with my Chief of Staff, Lieut. Gen. (then Maj . Gen.) Walter B. Smith. I instructed them to consider the plan in detail upon their arrival in England because, while agreeing with the broad scope of the operation and the selection of the assault area, I nevertheless felt that the initial assaulting forces were being planned in insufficient strength and committed on too narrow a front. This they did, and shortly after my arrival in London on 15 January, I was able, with them and my other commanders, to reach an agreement which altered the OVERLORD operation in this respect.

While my appointment as Supreme Commander did not become official until the receipt of a directive from the Combined Chiefs of Staff on 14 February, and while the status of my Headquarters-to be known as SHAEF-was not recognized until the following day, the basic work of planning continued during tI,is transitional period. The staff brought into being as COS SAC came under my control and was greatly expanded as the pressure of time and the vast scope of our work required.

I patterned my Headquarters upon the closely integrated Allied establishment which it had been my policy to maintain at AFHQ in the Mediterranean, and in this respect I was fortunate in obtaining for my staff men whose proved ability had already been demonstrated in previous campaigns - Air Chief Marshal Sir Arthur W. Tedder as my Deputy Supreme Commander, General Smith as my Chief of Staff, and Lieut. Gen. Sir Humfrey M. Gale as Chief Administrative Officer. General Morgan remained as Deputy Chief of Staff, his detailed knowledge of tactical plans making him absolutely indispensable.

Relationship between SHAEF and the Headquarters of my Commanders-in-Chief for the Navy, Army, and Air Forces was established on the operational planning level through a Joint Planning Staff which closely integrated the work of all. The Headquarters of COSSAC had been located at Norfolk House, St. James's Square, with an annex at 80, Pall Mall, and it was here initially that my own Headquarters came into being. However, I was convinced by past experience that a Headquarters located in the heart of a great city would not be as unified as one located elsewhere. Accordingly SHAEF was moved in March to Bushy Park, near Kingston-an-Thames. Here we studied the operation in detail and ironed out all the numerous and frequently vexing problems relating to so vast an undertaking.

The chief changes which we were to make in the assault plan were considered at the first meeting which I held with my Commanders-in-Chief at Norfolk House on 21 January. Field Marshal Montgomery (Commanding General, 21 Army Group), Admiral Sir Bertram H. Ramsay (Commander of the Allied Naval Expeditionary Force), and Air Chief Marshal Sir Trafford Leigh-Mallory (Commander of the Allied Expeditionary Air Force) reviewed operation OVERLORD as a whole with me and were in agreement upon certain amendments to the plan.

The COSSAC plan called for an initial assaulting force of three divisions. I had felt when I originally read the OVERLORD plan that our experiences in the Sicilian campaign were being misinterpreted, for, while that operation was in most respects successful, it was my conviction that had a larger assault force been employed against the island beachheads our troops would have been in a position to overrun the defenses more quickly. Against the better prepared defenses of France I felt that a tllree-division assault was in insufficient strength, and 3 that to attain success in this critical operation a minimum of five divisions should assault in the initial wave. Field Marshal Montgomery was in emphatic agreement with me on this matter, as were also Admiral Ramsay and Air Chief Marshal Leigh-Mallory, even though a larger assault force raised great new problems from both the naval and air points of view.

In addition to increasing the assault force from three to five divisions, I felt that the beach area to be attacked should be on a wider front than that originally envisaged. Particularly, it was considered that an attack directly against the Cotentin Peninsula should be included in the plan, with a view to the speedy conquest of Cherbourg. In the event that our troops were able to attain a high degree of surprise in the attack, they would be in a better position to overwhelm the strungout defenses before the enemy could regroup or mass for a counterattack. Conversely, in the event of strong resistance, we would be more advantageously situated, on a wider front and in greater force, to find "soft spots" in the defense.

The original COSSAC plan included the beachhead areas from Courseulles in the east to Grandcamp in the west. We decided to extend this area eastward to include the Ouistreham beaches, feeling that this would facilitate the seizure-by rapidly securing the eastern flank--of the important focal point of Caen and the vital airfields in tl,e vicinity. Westward, we decided that the assault front should be widened to include the Varreville beaches on the eastern side of the Cotentin Peninsula itself. A strong foothold on the peninsula and a rapid operation to cut its neck would greatly speed up the capture of the port of Cherbourg.

For the operation against the neck of the Cotentin to be successful, it was believed tlut two airborne divisions should be employed in support of the troops assaulting the Varreville beaches, still leaving one airborne division to hold vital bridges in the Orne-Dives Rivers area to the northeast of Caen. Field Marshal Montgomery and Admiral Ramsay were in agreement on this point, but Air Chief Marshal Leigh-Mallory saw technical difficulties which it was necessary to consider closely.

It was his feeling, both then and subsequently, that the employment of airborne divisions against the South Cotentin would result in landing losses to aircraft and personnel as high as 75%-80%. In the face of this estimate, however, I was still convinced of the absolute necessity of quickly overrunning the peninsula and attaining the port of Cherbourg, vital to the support and maintenance of our land forces. Without the airborne divisions an assault against the Varreville beaches would have been most hazardous, since our attack here could only be on a one-division front. Behind the landing beach was a lagoon, traversed only by a few causeways; the exits of these had to be captured from the rear, or else the strip of beach would quickly become a death trap. In addition, this beach was separated from the other four beaches to be assaulted by an estuary and marsh lands which would have effectively prevented the junction and link-up of the forces for several days, permitting the enemy in this sector more easily to dislodge us and threaten our right flank. Support by the airborne troops was essential, and I ultimately took upon myself the heavy responsibility of deciding that the airborne operation against the Cotentin be carried out. The decision, once taken, was loyally and efficiently executed by the airborne forces, and it is to them that immeasurable credit for the subsequent success of the western operation belongs. The airborne landing losses proved only a fraction of what had been feared, amounting in fact to less than 10%.

Our decisions to strengthen the forces employed in the initial assault, to widen the area of attack, and to employ the airborne forces in the Cotentin rather than at Caen, were communicated to the Combined Chiefs of Staff on 23 January, and at the same time I brought up the subject of the target date for the operation.

In the original plan, the target date for the D-day assault had been 1 May. A new factor, however, which made me doubt that the date could be adhered to was our deficiency in assault craft for the larger five-division attack. In the COSSAC plan, three divisions in the assault and two immediate follow-up divisions, a total of five, were to be preloaded in assault craft. Sufficient craft for five divisions had been planned. The new plan, calling for five divisions in the assault, still retained the two follow- up divisions, requiring therefore sufficient craft to preload seven divisions. There was considerable doubt that the additional craft could be made available by I May, and I informed the Combined Chiefs of Staff that, rather than risk failure with reduced forces on that date, postponement of the target date for a month would be preferable if I could be assured of then obtaining the strength required. My planners had advised me that a month's additional production of assault craft in both Great Britain and the United States would go far toward supplying the deficiency foreseen for the earlier date.

From the air point of view, the extension of the target date would afford a longer opportunity for the strategic bombing of Germany and the wearing down of German air strength. In addition, the tactical bombing of railheads and transportation centers, the preliminary softening of fortifications on the Channel coast, and the diversionary heavy air attacks in the Pas-de-Calais could be undertaken with greater thoroughness. The training of the invasion forces, and particularly the troop-carrier crews for the airborne operations, could also be carried on more thoroughly.

The Navy, moreover, desired additional time for the training of the assault craft crews and for the delivery and assembly of the extra vessels needed in the enlarged attack. From the naval viewpoint a postponement of the target date to the first of June was preferable to any briefer postponement, say of two weeks, since an early June date guaranteed the favorable tides necessary for the beach operations as well as a full moon.

From the strategic point of view the postponement seemed desirable, since weather conditions at the end of May would be likely to be more favorable for the mounting of a large-scale Russian offensive to assist the OVERLORD operation. Additionally, the situation in the Mediterranean might be sufficiently resolved by that time to preclude the necessity of an operation against the south of France closely coordinated with our western assault. The German forces in that theater might be so heavily engaged by our armies that a diversionary and containing assault would not be required in direct and immediate assistance to OVERLORD.

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