Operation Downfall was the military code name for the Allied plan for the invasion of Japan, when World War II was coming nearer to its end. The operation was going to become the largest and greatest amphibious assault in military history, but it never took place.

The planned operation was abandoned when Japan surrendered following the atomic bombings of Hiroshima and Nagasaki. Downfall consisted of 2 steps: Operation Olympic and Operation Coronet. The first one, which was set to begin in 1945, was intended to capture the southern third of the southernmost main Japanese island, Kyūshū. Operation Coronet, which was to take place in 1946, would be the invasion of the Kantō Plain. Actually, the plan of invasion was quite obvious for the Japanese, as the geography of the country wouldn't let the anti-German coalition act any other way. As the operation never happened, D-Day (or the operation Neptune, which took place on the 6th of June, 1944) remained (and still remains) the largest operation of a kind of all time.

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