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| combatant2 = | commander1 = | commander2 = | strength1 = | strength2 = | casualties1 = | casualties2 = | casualties3 = Civilian deaths: }} Operation Overlord was the code name for the Battle of Normandy, the Allied operation that launched the successful invasion of German-occupied western Europe during World War II. The operation commenced on 6 June 1944 with the Normandy landings (Operation Neptune, commonly known as D-Day). A 1,200-plane airborne assault preceded an amphibious assault involving more than 5,000 vessels. Nearly 160,000 troops crossed the English Channel on 6 June, and more than three million Allied troops were in France by the end of August. The decision to undertake a cross-channel invasion in 1944 was taken at the Trident Conference in Washington in May 1943. General Dwight D. Eisenhower was appointed commander of Supreme Headquarters Allied Expeditionary Force (SHAEF), and General Bernard Montgomery was named as commander of the 21st Army Group, which comprised all the land forces involved in the invasion. The Normandy coast was chosen as the site of the invasion, with the Americans assigned to land at Utah and Omaha Beaches, the British at Sword and Gold Beaches, and Canadians at Juno Beach. To meet the conditions expected on the Normandy beachhead, special technology was developed, including two artificial ports called Mulberry harbours and an array of specialised tanks nicknamed Hobart's Funnies. In the months leading up to the invasion, the Allies conducted a substantial military deception, Operation Bodyguard, using both electronic and visual misinformation. This misled the Germans as to the date and location of the main Allied landings. Adolf Hitler placed German Field Marshal Erwin Rommel in charge of developing fortifications all along the Atlantic Wall in anticipation of an invasion. The Allies failed to reach their goals for the first day, but gained a tenuous foothold that they gradually expanded as they captured the port at Cherbourg on 26 June and the city of Caen on 21 July. A failed counterattack by German forces on 8 August led to 50,000 soldiers of the German 7th Army being trapped in the Falaise pocket. The Allies launched an invasion of southern France (Operation Dragoon) on 15 August, and the Liberation of Paris followed on 25 August. German forces retreated across the Seine on 30 August 1944, marking the close of Operation Overlord. == Preparations for D-Day == In June 1940, German dictator Adolf Hitler had triumphed in what he called "the most famous victory in history"—the fall of France. The defending British Expeditionary Force, trapped along the northern coast of France, was able to evacuate over 338,000 troops to England in the Dunkirk evacuation (27 May to 4 June). British planners reported to Prime Minister 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 Germans invaded the Soviet Union in June 1941, Soviet leader Joseph Stalin began pressing for the creation of a second front in Western Europe. Churchill declined because, even with American help, he felt 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 Passchendaele and the Somme in 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 launched the invasion of French North Africa in November 1942, the invasion of Sicily in July 1943, and of Italy in September. These invasions provided the troops with valuable experience in amphibious warfare. The decision to undertake a cross-channel invasion within the next year was taken at the Trident Conference in Washington in May 1943. Churchill favoured making the main Allied thrust into Germany from the Mediterranean theatre, but was over-ruled by his American allies, who were providing the bulk of the men and equipment. 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 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 landings. 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 Spitfire and 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: Brittany, the Cotentin Peninsula, Normandy, and the Pas de Calais. As Brittany and Cotentin are peninsulas, it would have been possible for the Germans to cut off the Allied advance at a relatively narrow isthmus, so these sites were rejected. The Pas de Calais is the closest point in continental Europe to Britain and was the location of launch sites for V-1 and V-2 rockets, which were still under development. The Germans considered it to be the most likely initial landing zone, so it was the most heavily fortified region. It offered 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 hence 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 launch 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 SHAEF. General 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 that the scale of the initial invasion be expanded to five divisions, with airborne descents by three additional divisions, to allow operations on a wider front and speed up the capture of the port at Cherbourg. The need to acquire or produce extra landing craft for the expanded operation meant that the invasion had to be delayed to June. Eventually, 39 Allied divisions would be committed 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Operation Overlord」の詳細全文を読む スポンサード リンク
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