Downfall would have been the largest amphibious landing in history, including 42 aircraft carriers, 24 battleships, 400 destroyers and other ships. Fourteen U.S. divisions A division is a large military unit usually consisting of around ten to twenty thousand soldiers. would take part also as they used Okinawa as a staging base and then seized the southern portion of the island of Kyushu. The invasion was scheduled to start on November 1, 1945. But there were some other considerations that the planners had to take into account.
There was, naturally, to be a deception plan leading up to the Olympic invasion. By having such a plan it was hoped, as all deception plans in war were, that Allied casualties would be minimized because the enemy force would believe that it needed to focus itself elsewhere. The plan to precede Olympic was Operation Pastel, wherein which the Joint Chiefs of Staff would attempt to fool the Japanese into thinking that a direct invasion of the southern islands had been rejected and instead that the Allies would focus first on Japanese forces still in mainland China. The first strike would be a false Allied attack on China’s Chusan-Shanghai area, with a fictional landing date of October 1, 1945. This was to be followed by one of the smaller southern Japanese islands, Shikoku. After this the Allies hoped to surprise the Japanese with the Olympic invasion.
All of this was leading up to X-Day, as it was called, where the Alllied forces would invade Kyushu along the eastern, southeastern, southern and western coasts of the island near the towns of Miyazaki, Ariake, and Kushikino. The invasion force was to consist of three main groups landing on 35 different beaches, all codenamed after makes of automobiles. The Eastern Assault Force consisting of the 25th, 33rd and the 41st Infantry Divisions, would land near Miyaski and quickly move inland to capture Miyazaki and its nearby airfield. The Southern Force which was to consist of the 1st cavalry Division, the 43rd Division and American Division would land inside Ariake Bay and capture Shibushi and to capture, further inland, the city of Kanoya and its surrounding airfield. On the western shore of Kyushu near Kushikino the 2nd, 3rd, and 5th Marine Divisions would land and split, part of which would head inland to capture Sendai while the other half captured the port city of Kagoshima. Once these areas were secured more Allied reinforcements consisting of three American divisions would be brought in each month to strengthen the hold on the occupied portion of Kyushu.
Before and during all of this activity the U.S. Twentieth Air Force would be bombing strategic targets such as railroads, airfields and the various beaches that were to be hit. With a successful bombing campaign it was hoped that they could minimize any fast means that reinforcements could utilize to arrive at the various invasion points.
The four month timetable for Olympic was not to conquer the entire island but to gain a foothold for the Allies to jump off of and use as a staging ground for the even bigger invasion – Coronet. More on it in part 3.1The info for this piece came, once again, from Wikipedia, the the Combined Arms Research Library