Preparations for D-Day
In June 1940 Germany's leader
Adolf Hitler had triumphed in what he called "the most famous victory in history"—the
fall of France. British craft evacuated to England over 338,000 Allied troops trapped along the northern coast of France (including much of the
British Expeditionary Force (BEF)) in the
Dunkirk evacuation (27 May to 4 June). British planners reported to
Winston Churchill on 4 October that even with the help of other
Commonwealth countries and the United States, it would not be possible to regain a foothold in continental Europe in the near future. After the Axis
invaded the Soviet Union in June 1941, Soviet leader
Joseph Stalin began pressing for a
second front in Western Europe. Churchill declined because he felt that even with American help the British did not have adequate forces for such a strike, and he wished to avoid costly frontal assaults such as those that had occurred at the
World War I. Two tentative plans code-named
Operation Roundup and
Operation Sledgehammer were put forward for 1942–43, but neither was deemed by the British to be practical or likely to succeed. Instead, the
Allies expanded their activity in the Mediterranean, launching the
French North Africa in November 1942, the
invasion of Sicily in July 1943, and
invading Italy in September. These campaigns provided the troops with valuable experience in
Attendees at the
Trident Conference in Washington in May 1943 took the decision to launch a cross-Channel invasion within the next year. Churchill favoured making the main Allied thrust into Germany from the
Mediterranean theatre, but his American allies, who were providing the bulk of the men and equipment, over-ruled him. British Lieutenant-General
Frederick E. Morgan was appointed Chief of Staff, Supreme Allied Commander (COSSAC), to begin detailed planning. The initial plans were constrained by the number of available landing-craft, most of which were already committed in the Mediterranean and in the Pacific. In part because of lessons learned in the
Dieppe Raid of 19 August 1942, the Allies decided not to directly assault a heavily defended French seaport in their first landing. The failure at Dieppe also highlighted the need for adequate artillery and air support, particularly
close air support, and specialised ships able to travel extremely close to shore. The short operating-range of British aircraft such as the
Typhoon greatly limited the number of potential landing-sites, as comprehensive air-support depended upon having planes overhead for as long as possible. Morgan considered four sites for the landings:
Cotentin Peninsula, Normandy, and the
Pas de Calais. As Brittany and Cotentin are peninsulas, the Germans could have cut off the Allied advance at a relatively narrow isthmus, so these sites were rejected.
Pas de Calais, the closest point in continental Europe to Britain, was the location of launch sites for
V-2 rockets, then still under development.
[c] The Germans regarded it as the most likely initial landing zone, and accordingly made it the most heavily fortified region. It offered the Allies few opportunities for expansion, however, as the area is bounded by numerous rivers and canals, whereas landings on a broad front in Normandy would permit simultaneous threats against the port of
Cherbourg, coastal ports further west in Brittany, and an overland attack towards Paris and eventually into Germany. Normandy was therefore chosen as the landing site. The most serious drawback of the Normandy coast—the lack of port facilities—would be overcome through the development of artificial harbours.
The COSSAC staff planned to begin the invasion on 1 May 1944. The initial draft of the plan was accepted at the
Quebec Conference in August 1943. General
Dwight D. Eisenhower was appointed commander of
Bernard Montgomery was named commander of the
21st Army Group, which comprised all of the land forces involved in the invasion. On 31 December 1943, Eisenhower and Montgomery first saw the COSSAC plan, which proposed amphibious landings by three
divisions, with two more divisions in support. The two generals immediately insisted on expanding the scale of the initial invasion to five divisions, with airborne descents by three additional divisions, to allow operations on a wider front and to speed up the capture of the port at Cherbourg. The need to acquire or produce extra landing craft for the expanded operation meant delaying the invasion until June 1944. Eventually the Allies committed 39 divisions to the Battle of Normandy: 22 American, 12 British, three Canadian, one Polish, and one French, totalling over a million troops all under overall British command.
Allied invasion plan
assault routes into Normandy
"Overlord" was the name assigned to the establishment of a large-scale
lodgement on the Continent. The first phase, the amphibious invasion and establishment of a secure foothold, was code-named
Operation Neptune. To gain the required air superiority needed to ensure a successful invasion, the Allies launched a bombing campaign (codenamed
Operation Pointblank) to target German aircraft-production, fuel supplies, and airfields. Under the
Transport Plan, communications infrastructure and road and rail links were bombed to cut off the north of France and to make it more difficult to bring up reinforcements. These attacks were widespread so as to avoid revealing the exact location of the invasion. Elaborate
deceptions were planned to prevent the Germans from determining the timing and location of the invasion.
The coastline of Normandy was divided into seventeen sectors, with codenames using a
spelling alphabet—from Able, west of
Omaha, to Roger on the east flank of
Sword. Eight further sectors were added when the invasion was extended to include
Utah on the Cotentin Peninsula. Sectors were further subdivided into beaches identified by the colours Green, Red, and White.
Allied planners envisaged preceding the sea-borne landings with airborne drops: near Caen on the eastern flank to secure the
Orne River bridges, and north of
Carentan on the western flank. The initial goal was to capture Carentan,
Bayeux, and Caen. The Americans, assigned to land at Utah and Omaha, were to cut off the Cotentin Peninsula and capture the port facilities at Cherbourg. The British at Sword and
Gold, and the Canadians at
Juno, were to capture Caen and form a front line from
Caumont-l'Éventé to the south-east of Caen in order to protect the American flank, while establishing airfields near Caen. Possession of Caen and its surroundings would give the Anglo-Canadian forces a suitable staging area for a push south to capture the town of
Falaise. A secure lodgement would be established and an attempt made to hold all territory captured north of the
Avranches-Falaise line during the first three weeks. The Allied armies would then swing left to advance towards the
The invasion fleet, led by Admiral Sir
Bertram Ramsay, was split into the Western Naval Task Force (under Admiral
Alan G Kirk) supporting the American sectors and the Eastern Naval Task Force (under Admiral Sir
Philip Vian) in the British and Canadian sectors. The American forces of the
First Army, led by Lieutenant General
Omar Bradley, comprised
VII Corps (Utah) and
V Corps (Omaha). On the British side, Lieutenant-General
Miles Dempsey commanded the
Second Army, under which
XXX Corps was assigned to Gold and
I Corps to Juno and Sword. Land forces were under the overall command of Montgomery, and air command was assigned to
Air Chief Marshal Sir
Trafford Leigh-Mallory. The
First Canadian Army included personnel and units from
Poland, Belgium, and the Netherlands. Other Allied nations also participated.
Map of the air plan for the Allied landing in Normandy
Allied Expeditionary Air Force undertook over 3,200 photo-reconnaissance sorties from April 1944 until the start of the invasion. Photos of the coastline were taken at extremely low altitude to show the invaders the terrain, obstacles on the beach, and defensive structures such as bunkers and gun emplacements. To avoid alerting the Germans as to the location of the invasion, this work had to be undertaken over the entire European coastline. Inland terrain, bridges, troop emplacements, and buildings were also photographed, in many cases from several angles, to give the Allies as much information as possible. Members of
Combined Operations Pilotage Parties clandestinely prepared detailed harbour maps, including
An appeal for holiday pictures and postcards of Europe announced on the
BBC produced over ten million items, some of which proved useful. Information collected by the
French resistance helped provide details on Axis troop movements and on construction techniques used by the Germans for bunkers and other defensive installations.
Many German radio messages were encoded using the
Enigma machine and other enciphering techniques and the codes were changed frequently. A team of code breakers stationed at
Bletchley Park worked to break codes as quickly as possible to provide advance information on German plans and troop movements. British military intelligence code-named this information
Ultra intelligence as it could only be provided to the top level of commanders. The Enigma code used by Field Marshal
Gerd von Rundstedt, Oberbefehlshaber West (Supreme Commander West;
OB West), commander of the
Western Front, was broken by the end of March. German intelligence changed the Enigma codes right after the Allied landings of 6 June but by 17 June the Allies were again consistently able to read them.
In response to the lessons learned at the disastrous Dieppe raid, the Allies developed new technologies to help ensure the success of Overlord. To supplement the preliminary offshore bombardment and aerial assaults, some of the landing craft were equipped with artillery and anti-tank guns to provide close supporting fire. The Allies had decided not to immediately attack any of the heavily protected French ports and two artificial ports, called
Mulberry harbours, were designed by COSSAC planners. Each assembly consisted of a floating outer
breakwater, inner concrete
Phoenix breakwaters) and several floating piers. The Mulberry harbours were supplemented by
blockship shelters (codenamed "Gooseberries"). With the expectation that fuel would be difficult or impossible to obtain on the continent, the Allies built a "Pipe-Line Under The Ocean" (
PLUTO). Specially developed pipes 3 inches (7.6 cm) in diameter were to be laid under the Channel from the
Isle of Wight to Cherbourg by D-Day plus 18. Technical problems and the delay in capturing Cherbourg meant the pipeline was not operational until 22 September. A second line was laid from
Dungeness to Boulogne in late October.
The British military built a series of specialised tanks, nicknamed
Hobart's Funnies, to deal with conditions expected during the Normandy campaign. Developed under the supervision of Major-General
Percy Hobart, these were specially modified
M4 Sherman and
Churchill tanks. Examples include the
Sherman Crab tank (equipped with a mine flail), the
Churchill Crocodile (a flame-throwing tank), and the
Armoured Ramp Carrier, which other tanks could use as a bridge to scale sea-walls or to overcome other obstacles. In some areas, the beaches consisted of a soft clay that could not support the weight of tanks. The "
bobbin" tank would overcome this problem by deploying a roll of matting over the soft surface and leaving the material in place as a route for more conventional tanks. The
Armoured Vehicle Royal Engineers (AVREs) were modified for many tasks, including laying bridges and firing large charges into
pillboxes. The Duplex-Drive tank (
DD tank), another design developed by Hobart's group, was a self-propelled amphibious tank kept afloat using a waterproof canvas screen inflated with compressed air. These tanks were easily swamped, and on D-Day many sank before reaching the shore, especially at Omaha.
In the months leading up to the invasion, the Allies conducted
Operation Bodyguard, the overall strategy designed to mislead the Germans as to the date and location of the main Allied landings.
Operation Fortitude included Fortitude North, a misinformation campaign using fake radio-traffic to lead the Germans into expecting an attack on Norway, and Fortitude South, a major deception designed to fool the Germans into believing that the landings would take place at Pas de Calais in July. A fictitious
First U.S. Army Group was invented, supposedly located in
Sussex under the command of Lieutenant General
George S. Patton. The Allies constructed dummy tanks, trucks, and landing craft, and positioned them near the coast. Several military units, including
II Canadian Corps and
2nd Canadian Division, moved into the area to bolster the illusion that a large force was gathering there. As well as the broadcast of fake radio-traffic, genuine radio messages from 21st Army Group were first routed to Kent via landline and then broadcast, to give the Germans the impression that most of the Allied troops were stationed there. Patton remained stationed in England until 6 July, thus continuing to deceive the Germans into believing a second attack would take place at Calais. Military and civilian personnel alike were aware of the need for secrecy, and the invasion troops were as much as possible kept isolated, especially in the period immediately before the invasion. One American general was sent back to the United States in disgrace after revealing the invasion date at a party.
The Germans thought they had an extensive network of spies operating in the UK, but in fact all their agents had been captured, and some had become
double agents working for the Allies as part of the
Double-Cross System. The double agent
Juan Pujol García, a Spanish opponent of the Nazis known by the code name "Garbo", developed over the two years leading up to D-Day a fake network of informants that the Germans believed were collecting intelligence on their behalf. In the months preceding D-Day, Pujol sent hundreds of messages to his superiors in Madrid, messages specially prepared by the British intelligence service to convince the Germans that the attack would come in July at Calais.
Many of the German radar stations on the French coast were destroyed by the RAF in preparation for the landings. On the night before the invasion, in
No. 617 Squadron RAF dropped strips of "window",
metal foil that caused a radar return mistakenly interpreted by German radar operators as a naval convoy. The illusion was bolstered by a group of small vessels towing
No. 218 Squadron RAF also dropped "window" near
Operation Glimmer. On the same night, a small group of
Special Air Service (SAS) operators deployed dummy paratroopers over
Le Havre and Isigny. These dummies led the Germans to believe an additional airborne assault had occurred.
Rehearsals and security
Training exercises for the Overlord landings took place as early as July 1943. As the nearby beach resembled the planned Normandy landing-site, the town of
Slapton in Devon, was evacuated in December 1943 and taken over by the armed forces as a site for training exercises that included the use of landing craft and the management of beach obstacles. Near Slapton on 28 April 1944 749 American soldiers and sailors died when
German torpedo-boats surprised members of Assault Force "U" conducting
Exercise Tiger. Exercises with landing craft and live ammunition also took place at the Combined Training Centre in
Inveraray in Scotland. Naval exercises took place in Northern Ireland, and medical teams in London and elsewhere rehearsed how they would handle the expected waves of casualties. Paratroopers conducted exercises, including a huge demonstration drop on 23 March 1944 observed by Churchill, Eisenhower, and other top officials.
Allied planners considered tactical surprise to be a necessary element of the plan for the landings. Information on the exact date and location of the landings was provided only to the topmost levels of the armed forces. Men were sealed into their marshalling areas at the end of May, with no further communication with the outside world. Troops were briefed using maps that were correct in every detail except for the place names, and most were not told their actual destination until they were already at sea. A news blackout in Britain increased the effectiveness of the deception operations. Travel to and from the
Republic of Ireland was banned, and movement within several kilometres of the coast of England restricted.
Men of the British 22nd Independent Parachute Company,
6th Airborne Division
being briefed for the invasion, 4–5 June 1944
The invasion planners specified a set of conditions regarding the timing of the invasion, deeming only a few days in each month suitable. A full moon was desirable, as it would provide illumination for aircraft pilots and have the
highest tides. The Allies wanted to schedule the landings for shortly before dawn, midway between low and high tide, with the tide coming in. This would improve the visibility of obstacles the enemy had placed on the beach while minimising the amount of time the men had to spend exposed in the open. Specific criteria were also set for wind speed, visibility, and cloud cover. Eisenhower had tentatively selected 5 June as the date for the assault. However, on 4 June, conditions were clearly unsuitable for a landing; high winds and heavy seas made it impossible to launch landing craft, and low clouds would prevent aircraft from finding their targets.
By the evening of 4 June, the Allied meteorological team, headed by Group Captain
James Stagg of the
Royal Air Force, predicted that the weather would improve sufficiently so that the invasion could go ahead on 6 June. He met Eisenhower and other senior commanders at their headquarters at
Southwick House in Hampshire to discuss the situation. General Montgomery and Major General
Walter Bedell Smith, Eisenhower's chief of staff, were eager to launch the invasion. Admiral Bertram Ramsay was prepared to commit his ships, while Air Chief Marshal Trafford Leigh-Mallory expressed concern that the conditions would be unfavourable for Allied aircraft. After much discussion, Eisenhower decided that the invasion should go ahead. Allied control of the Atlantic meant that German meteorologists did not have access to as much information as the Allies on incoming weather patterns. As the Luftwaffe meteorological centre in Paris predicted two weeks of stormy weather, many Wehrmacht commanders left their posts to attend war games in
Rennes, and men in many units were given leave. Marshal
Erwin Rommel returned to Germany for his wife's birthday and to meet Hitler to try to get more Panzers.
Had Eisenhower postponed the invasion, the next available period with the right combination of tides (but without the desirable full moon) was two weeks later, from 18 to 20 June. As it happened, during this period the invaders would have encountered a major storm lasting four days, between 19 and 22 June, that would have made the initial landings impossible.
German preparations and defences
Nazi Germany had at its disposal 50 divisions in France and the Low Countries, with another 18 stationed in Denmark and Norway.
[e] Fifteen divisions were in the process of formation in Germany, but there was no strategic reserve. The Calais region was defended by the
15th Army under
Generaloberst (Colonel General)
Hans von Salmuth, and Normandy by the
7th Army commanded by
Friedrich Dollmann. Combat losses throughout the war, particularly on the
Eastern Front, meant the Germans no longer had a pool of able young men from which to draw. German soldiers were now on average six years older than their Allied counterparts. Many in the Normandy area were
Ostlegionen (eastern legions)—conscripts and "volunteers" from
Turkestan, Russia, Mongolia, and elsewhere. The Wehrmacht had provided them mainly with unreliable captured equipment; they lacked motorised transport. Formations that arrived later, such as the
12th SS Panzer Division Hitlerjugend, were for the most part younger and far better equipped and trained than the static troops stationed along the coast.
Alarmed by the raids on
St Nazaire and Dieppe in 1942, Hitler ordered the construction of fortifications all along the Atlantic coast, from Spain to Norway, to protect against an expected Allied invasion. He envisioned 15,000 emplacements manned by 300,000 troops, but due to shortages, particularly of concrete and manpower, most of the
strongpoints were never built. As the expected site of an Allied invasion, Pas de Calais was heavily defended. In the Normandy area the best fortifications were concentrated at the port facilities at Cherbourg and
A report by Rundstedt to Hitler in October 1943 regarding the weak defences in France led to the appointment of Rommel to oversee the construction of further fortifications along the expected invasion-front, which stretched from the Netherlands to Cherbourg. Rommel was given command of the newly re-formed
Army Group B, which included the 7th Army, the 15th Army, and the forces guarding the Netherlands. Nazi Germany's tangled command structure made it difficult for Rommel to achieve his task. He was not allowed to give orders to the
Organisation Todt, which was commanded by armaments minister
Albert Speer, so in some places he had to assign soldiers to do construction work.
Rommel believed that the Normandy coast could be a possible landing point for the invasion, so he ordered the construction of extensive defensive works along that shore. In addition to concrete gun-emplacements at strategic points along the coast, he ordered wooden stakes, metal tripods, mines, and large anti-tank obstacles to be placed on the beach to delay the approach of landing craft and to impede the movement of tanks. Expecting the Allies to land at high tide so that the infantry would spend less time exposed on the beach, he ordered many of these obstacles to be placed at the high-tide mark. Tangles of barbed wire, booby traps, and the removal of ground cover made the approach hazardous for infantry. On Rommel's order, the number of mines along the coast was tripled. Given the Allied air supremacy (4,029 Allied aircraft assigned to operations in Normandy plus 5,514 aircraft assigned to bombing and defence, versus 570 Luftwaffe planes stationed in France and the Low Countries), booby-trapped stakes known as Rommelspargel (
Rommel's asparagus) were set up in meadows and fields to deter airborne landings.
Rommel, believing that the Germans' best chance was to stop the invasion at the shore, requested that mobile reserves—especially tanks—be stationed as close to the coast as possible. Rundstedt, General
Leo Geyr von Schweppenburg (commander of
Panzer Group West), and other senior commanders believed that the invasion could not be stopped on the beaches. Geyr argued for a conventional doctrine: keeping the Panzer formations concentrated in a central position around Paris and Rouen and deploying them only when the main Allied beachhead had been identified. Geyr also noted that in the
Italian Campaign the armour stationed near the coast had been damaged by naval bombardment. Rommel's opinion was that because of the overwhelming Allied air superiority, large-scale movement of tanks would not be possible once the invasion was underway. Hitler made the final decision: he left three divisions under Geyr's command and gave Rommel operational control of three tank-divisions as reserves. Hitler took personal control of four divisions as strategic reserves, not to be used without his direct orders.