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Operation Downfall was the codename for the Allied plan for the invasion of Japan near the end of World War II. The planned operation was abandoned when Japan surrendered following the atomic bombings of Hiroshima and Nagasaki and the Soviet declaration of war.〔Giangreco (2009) pg. xvi〕 The operation had two parts: Operations Olympic and Coronet. Set to begin in October 1945, Operation Olympic was intended to capture the southern third of the southernmost main Japanese island, Kyūshū, with the recently captured island of Okinawa to be used as a staging area. Later, in spring 1946, Operation Coronet was the planned invasion of the Kantō Plain, near Tokyo, on the Japanese island of Honshū. Airbases on Kyūshū captured in Operation Olympic would allow land-based air support for Operation Coronet. If Downfall had taken place, it would have been the largest amphibious operation in history.〔.〕 Japan's geography made this invasion plan quite obvious to the Japanese as well; they were able to predict the Allied invasion plans accurately and thus adjust their defensive plan, Operation ''Ketsugō'', accordingly. The Japanese planned an all-out defense of Kyūshū, with little left in reserve for any subsequent defense operations. Casualty predictions varied widely, but were extremely high. Depending on the degree to which Japanese civilians would have resisted the invasion, estimates ran up into the millions for Allied casualties. ==Planning== Responsibility for planning Operation Downfall fell to American commanders Fleet Admiral Chester Nimitz, General of the Army Douglas MacArthur and the Joint Chiefs of Staff—Fleet Admirals Ernest King and William D. Leahy, and Generals of the Army George Marshall and Hap Arnold (the latter being the commander of the US Army Air Forces). Douglas MacArthur at the time was also being considered for promotion to a special "super rank" of General of the Armies, so as to be granted operational authority over other five-star officers. However, the proposal to promote MacArthur was only at the level of informal discussion by the time World War II ended. At the time, the development of the atomic bomb was a very closely guarded secret (not even then Vice President Harry Truman knew of its existence until he became President), known only to a few top officials outside the Manhattan Project, and the initial planning for the invasion of Japan did not take its existence into consideration. Once the atomic bomb became available, General Marshall envisioned using it to support the invasion if sufficient numbers could be produced in time. Throughout the Pacific War, the Allies were unable to agree on a single Commander-in-Chief (C-in-C). Allied command was divided into regions: by 1945, for example, Chester Nimitz was the Allied C-in-C Pacific Ocean Areas, while Douglas MacArthur was Supreme Allied Commander, South West Pacific Area, and Admiral Louis Mountbatten was the Supreme Allied Commander, South East Asia Command. A unified command was deemed necessary for an invasion of Japan. Interservice rivalry over who it should be (the United States Navy wanted Nimitz, but the United States Army wanted MacArthur) was so serious that it threatened to derail planning. Ultimately, the Navy partially conceded, and MacArthur was to be given total command of all forces, if circumstances made it necessary. 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 Downfall」の詳細全文を読む スポンサード リンク
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