TWO YEARS of planning and preparation led up to the Allied landings in Normandy on 6 June 1944. British and American staffs had to work out every foreseeable detail for an undertaking that would involve the major military resources of the two Allied powers; immense stocks of shipping, aircraft, and supplies were assembled in the British Isles in an effort that taxed the war industries of both countries; before D Day the Allied air forces had carried out several months of bombing operations which were an integral part of the invasion itself.
The first decisions were strategic in the broadest sense, since the opening of a front in Western Europe had to be considered in reference to over-all Allied plans for offensive operations against Germany, as well as the developments of the war in Russia and of the war against Japan. In May 1943 the Anglo-American conference in Washington concluded this stage of strategic planning; Prime Minister Churchill and President Roosevelt together with their highest military advisers decided to launch an offensive in 1944 against Hitler's Atlantic Wall.
Allied planners, after weighing all the possibilities, finally selected 50 miles of coast in western Normandy, from the Vire Estuary to the Orne, as the assault area for securing a lodgement. This area was near good, relatively undamaged ports in southern and southwestern England, and was in range of fighter planes operating from English bases; the major French ports of Cherbourg and le Havre were within striking distance; and air attacks on railways and river bridges might be able to isolate the region behind the assault area from the main enemy centers of supply and reinforcement to the east. In comparison with the stretch of coast northeast of the Seine (Pas-de-Calais), along the narrowest part of the English Channel, western Normandy was somewhat further from English bases but was not as heavily fortified. At the Quebec Conference in August 1943 Allied leaders approved the choice of this battleground for invasion.
The staffs of ground forces, air forces, and navies had now entered the second stage of planning for the largest amphibious operation in military history. The tactical difficulties to be faced were only one part of a problem that required complete coordination and teamwork, not merely between the military forces of two nations but also between all arms of those forces. Planning necessarily included preparation for operations over an extended period of time, and had to cover far more than the initial task of securing beachheads. In some respects the critical factor was the Allies' ability to reinforce and supply the assault rapidly enough both to meet enemy counterattacks and to prepare for a larger Allied offensive beyond the landing area. The Allied navies and services of supply had to solve logistical problems on which would depend the fate of the whole undertaking.
In this phase of planning, as main policies were worked out in ever more complex detail by staffs of subordinate commands, the work was coordinated under the Chief of Staff, Supreme Allied Command, Lt. Gen. Sir Frederick E. Morgan. In his organization, British and American officers of all the services worked side by side in shaping their joint enterprise. The fusion of Allied planning staffs under a single command involved a principle which was carried into the command organization for the operation itself. On 21 January 1944 Gen. Dwight D. Eisenhower, called from the North African Theater of Operations, had his first meeting with the high Allied planning staff in England. He took formal command at Supreme Headquarters, Allied Expeditionary Forces, on 13 February.
Planning now approached the final stage. The approximate target date (Y Day) had been set as 31 May, after earlier designation as 1 May; the postponement was made in order to obtain a larger supply of assault craft and to give more time for the preliminary air operations to produce their desired effect. By February, the staffs of higher commands had finished their plans, which would determine the major outline of the assault, and the plans of lower echelons were nearing completion. What remained was the difficult task of shaping last details, with due regard to ever increasing intelligence of enemy defenses and to the experience gained in training exercises. Final loading plans, among the most complex features of the whole operation, were subject to change as late as May because of uncertainties as to the number of ships and craft available.
Services of Supply, commanded by Lt. Gen. John C. H. Lee, was completing its program of mounting the supplies for an operation which has been described as "an assault of materiel, operated by man." Planning for this aspect of the invasion had begun in April 1942, and along with it went the work of preparing facilities and assembling stores, work which was interrupted by the need to furnish 50,000 tons of cargo for the invasion of North Africa in November 1942. By June 1944 the number of United States troops in the United Kingdom had risen to 1,526,965, half of them arriving after the end of 1943. The stock pile for invasion--over and above basic loads and equipment--was 2,500,000 tons. In the process of mounting the assaults, 1,200 troop concentration camps and 100 marshaling camps had to be set up and operated, and 144,000 tons of supplies were preloaded, waiting for D Day.
Allied naval forces in the NEPTUNE operation, commanded by Admiral Sir Bertram H. Ramsay, faced a task of primary importance. They had to convey the ground forces to the area for assault on a hostile and defended shore, assist their landings by gunfire support, protect their lines of communication against enemy surface and underwater attack, and insure the flow of supplies for an indefinite period of future operations. Some 4,100 ships and craft of all types were involved in the assault, including major units of both British and American fleets.
Navy and Air Forces
The Allied air forces, under command of Air Chief Marshal Sir Traford L. Leigh-Mallory, were assigned a complex role both defensive and offensive in character. They would protect the huge assault convoy at every stage on its approach to Normandy and throughout the battle for the beaches. Offensively, they had the mission of assisting the operation by landings of airborne troops, by air bombardment of coastal defenses, and by attacks on enemy lines of reinforcement and supply.
In a very real sense, the invasion began with air force operations that had commenced long before D Day. From the summer of 1943 to the following spring, the U. S. Eighth Air Force had concentrated its attacks on German aircraft industries and airfields, with the primary purpose of preventing the enemy from increasing his strength in the air. Both by destruction of factories and of enemy planes met in combat this program was successful, and its success counted in the invasion. In addition to losing between 5,000 and 6,000 planes in the period, the enemy was unable to enlarge his first-line force in preparation for the expected assault.
In April and May 1944, while continuing attacks on Germany often enough to force concentration of enemy air strength in that area, the heavy bombers entered on a phase of operations directly related to the impending assault. This was a series of heavy attacks on marshaling yards and airfields in France, the Low Countries, and western Germany, over an area large enough to preclude any indication of the precise invasion area. The attack on marshaling yards was designed to paralyze repair and maintenance facilities, thus wearing down the capacity of railways for movement of troops and supplies and forcing the enemy to maximum use of road transport. During May the range of air attacks was gradually narrowed, coming to a climax in the three days preceding D Day. However, even in this period of final blows against rail junctions and airfields a majority of the targets were along the Channel coast east of the Seine.
Ninth Air Force medium bombers and fighter-bombers had also shared in the preparatory phases of the campaign. Beginning in April and continuing with increased vigor in May, they delivered attacks on enemy airfields in northern France, with the aim of ultimately neutralizing all fields within 130 miles of the assault beaches. During May, 36 airfields from Brittany to Holland received one or more attacks. Marshaling yards were also a target of medium bombers; between 1 March and 5 June, 36 yards in Belgium and northern France were hit in a total of 139 attacks. Results were excellent. The important yard at Creil, near Paris, was estimated as 60 percent out of commission on 24 May. Late in that month, rail bridges on the Seine and the Meuse Rivers were given first priority. By 4 June, all rail bridges (10) between Rouen and Conflans, inclusive, were knocked out, and all but 1 of the 14 road bridges. Fighter-bomber attacks on enemy rolling stock during May inflicted considerable damage. On 21 May, in the most active day for this type of work, 500 aircraft claimed results of 46 locomotives destroyed and 32 damaged, and damage to 30 trains. The Ninth Air Force was also busy on reconnaissance missions, which included heavy activity north of the Somme River as well as in the invasion area.
Bomber Command of the Royal Air Force switched the main effort of its attacks during May from Germany to France and the Low Countries. Of 37,250 tons dropped during the month, 28,703 were directed at targets which were chosen as part of the "softening-up" program leading to the invasion.
The ground forces in the Normandy operation were led by Gen. Sir Bernard L. Montgomery, commanding 21 Army Group. His troops would assault in three main areas (Map No. I)1 with initial strength of six reinforced infantry divisions landing from the sea and of three airborne divisions.
21 Army Group
Map No. 1: Disposition of German Forces in the West -- 6 June 1944
On the left the Second British Army would attack with three divisions (two of I Corps, one of XXX Corps) on three landing beaches. A brigade of the 6 British Airborne Division was to be dropped behind the beach defenses to secure vital bridges over the Orne River, between Caen and the sea. The objectives for D Day of the Second British Army included Bayeux, Caen, and Cabourg.
The First U. S. Army, commanded by Lt. Gen. Omar N. Bradley, was responsible for the other two assault areas. VII Corps (Maj. Gen. J. Lawton Collins, commanding) would land one division just north of the Vire Estuary (Beach "Utah"). In the early morning hours of D Day, four to five hours before the assault from sea, the 82d and 101st Airborne Divisions were scheduled to be dropped in the area southeast and west of Ste-Mere-Eglise, where their mission was to capture the crossings of the Merderet River, secure the line of the Douve River as a barrier to the south, and assist the landings at Utah Beach. At the end of D Day, VII Corps should control the area east of the Merderet from just south of Montebourg to the Douve.
Between the other assault areas, V Corps, commanded by Maj. Gen. Leonard T. Gerow planned its attack on a 7,000-yard stretch of beach to be known as "Omaha."2 The scheme and objectives of this assault will be described later in detail.
General Montgomery's intention after the initial beachheads were secured, was to hold in the area south and east of Caen while the First U. S. Army meantime maneuvered to cut of the Cotentin peninsula and capture Cherbourg. This port, to be opened as a major supply channel for further operations, was to be taken by D+15. The First Army, reinforced to a strength of three corps, was then to attack south toward Coutances and the base of the Brittany peninsula. Tentative phase lines allowed for capture of the Cerisy Forest area by D+5 or 6; St-Lo and Caumont by D+9. These phase lines were set with the most favorable possible development of the operation in mind. They insured readiness for maximum progress but represented neither a hard-and-fast schedule nor an optimistic forecast.
Enemy strength in France and the Low Countries (Map No. 1) was estimated at 60 divisions, having been built up from 53 since February 1944. Of these, 17 were infantry divisions, 26 were characterized as "limited employment" units (coastal defense units of limited mobility), 7 were training units, and 10 were panzer or panzer grenadier divisions. The armored divisions were located at inland points whence they could be moved as striking forces into a threatened coastal area. As a possible indication of where the German high command expected the assault, no fewer than 22 divisions guarded the region from the Seine to Holland.
The sector in which the blow was actually to fall came under the German Seventh Army, commanded by Col. Gen. Friedrich Dollmann with headquarters at le Mans in Normandy. LXXXIV Corps was responsible for the defense of the French coast from the Orne River to the northeast corner of Brittany. At the end of the winter the enemy force in or very near the assault area was estimated at only five infantry divisions, plus minor ground force elements. During May, Allied intelligence found evidence of reinforcement by two infantry divisions and (just south of Caen) the 21st Panzer Division. As a mobile reserve, two panzer divisions had come into the Alencon-Evreux region, from which they could reach the assault area quickly. A number of the enemy units in Brittany would also be available as reinforcement within a few days, and (depending
on the success of Allied air attacks) divisions from north of the Seine and south of the Loire could be brought to Normandy. Allied estimates of enemy build-up, assuming no interference to his road and rail movement, fixed his maximum possible strength in the assault area at 18 to 20 divisions, including 8 armored, by D+3.
At this same date Allied forces ashore were scheduled to number 13 divisions, including elements of 2 armored divisions.3 The success of the invasion would depend in considerable measure on the outcome of a race between Allied build-up and enemy reinforcement, in which it was hoped that the operations of the Allied air forces against rail and road communications would impose a decisive handicap on the Germans.
As the highest U. S. Army field-force headquarters then in Britain, V Corps Headquarters began in July 1943 to share in the early planning for employment of American forces in assault on the continent. On 12 September, by directive of the Chief of Staff, Supreme Allied Headquarters, V Corps' work was focused on the specific problem of an assault landing in Normandy. By October the headquarters of First U. S. Army and U. S. 1st Army Group were established in Britain. Since the decisions taken at higher levels determined the mission and objectives of subordinate units, the work had to be done concurrently and with constant interchange of views between the different levels of command and between the different services. The final plans for ground forces were produced in a series from January to May, beginning with 21 Army Group. First Army NEPTUNE Plan was issued on 25 February, V Corps' plan on 26 March, and that of the 1st Infantry Division on 16 April. No final decisions on troop lists and loading were possible until even later dates, and revisions of detail in many parts of the plans were necessary as late as the end of May.
V Corps Planning
A special planning group, headed by Col. Benjamin B. Talley, had been put in charge of shaping the V Corps NEPTUNE Plan. As the First Army and V Corps planning groups proceeded in their work, they felt the necessity of practical experiment with the problems involved in an amphibious operation on the scale proposed, particularly those of mounting and loading assault troops. A training center at Ilfracombe, northwest Devonshire, for study of assault techniques had been in use since 1942, and experiments on methods of loading and landing had been conducted near Dartmouth since September 1943 with cooperation of the British Navy. In December a stretch of coast at Slapton Sands (South Devonshire) was provided by the British Government as an assault training area for American forces. Here the conditions of tide, beach, and terrain were roughly similar to those on the Normandy coast, and the area was large enough to permit large-scale exercises and the use of live fire including naval and air bombardment. From January on, this training ground was used for every type of experiment and for exercises involving naval, air force, and service force units as well as the assault infantry and tanks.
In addition to its training value, the work done here was of direct influence on the planning, particularly in the case of exercises conducted on a scale large enough to embrace major units. Exercise "Duck," held in January, involved a division plus corps troops and took in all the stages of assault from concentration and marshaling to a landing after air bombardment and naval fire. From this exercise it was learned that three divisions could be mounted from the Plymouth-Portland-Falmouth-Dartmouth
port areas, instead of one as previously supposed. In March, Exercise "Fox" was staged at corps level and involved two divisions. From 3 to 8 May, "Fabius I" concluded the series of larger exercises with what amounted to a dress rehearsal for the NEPTUNE operation. The troops used a scheme of maneuver closely similar to that of the NEPTUNE plans, and the concentration and embarkation took place in areas soon to be used for NEPTUNE mounting. Throughout these months, training and planning went hand in hand, and the Planning Group used lessons learned at Slapton Sands in its final adjustments and revision of details. V Corps NEPTUNE Plan, consisting of an operations plan proper and 22 annexes (practically all of these completed by revisions in April or May), totaled 326 legal-size pages with 23 maps and charts.
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 Maps numbered in roman are bound in sequence on the inside of the back cover.
 From "O" Force, assigned to the area.
 Also several British and U.S. tank units attached to infantry divisions or employed as corps troops.