"During the early part of 1945, as the Joint Chiefs of Staff discussed plans to force the unconditional surrender of Japan, General MacArthur's staff in Australia undertook intelligence studies to assess Japanese defensive capabilities remaining in the home islands. On 24 March, General MacArthur's G-2 issued the first official intelligence report concerning the yet unnamed operation to invade Japan; G-2 Estimate of the Enemy Situation With Respect to Operations Against Kyushu and Honshu. This report was a strategic overview of what naval, air, and ground forces the Japanese currently had which could oppose an Allied invasion scheduled for the fall of 1945. This preliminary report estimated that by the fall of 1945, three divisions would be deployed in southern Kyushu, three divisions in northern Kyushu, and up to four divisions could reinforce from Honshu. The intelligence estimate assessed that ten combat divisions were the maximum the Japanese could tactically employ on Kyushu.(1) General MacArthur's staff used this initial estimate of ten combat divisions as the basis for the early planning for Operation Olympic.
The second intelligence estimate to be published was much more detailed and specific in regard to the location of Operation Olympic. The USAFPAC G-2 Estimate of the Enemy Situation With Respect to an Operation Against Southern Kyushu in November 1945 was issued on 25 April 1945. It identified the Japanese Sixteenth Area Army, headquartered at Fukuoka, as having the responsibility for the defense of Kyushu. It was believed that Japanese planners would assign six combat divisions (plus two depot divisions) to garrison Kyushu initially, and that they were prepared to expend up to ten combat divisions. Air reconnaissance identified depot facilities in northern Kyushu to maintain such a force.(2) As first identified in the March estimate, it was expected that three of the divisions would be deployed in southern Kyushu and three north of the central mountain mass. The 25 April intelligence estimate addressed forces in southern and northern Kyushu as two distinct elements. The geographical feature of the central mountain region in Kyushu was assessed to pose a major obstacle in the Japanese coordination of forces between northern and southern Kyushu.
The 25 April document assessed the Japanese strength in southern Kyushu to be between 80,000 to 85,000 troops, of all classes. It estimated that by 1 November 1945, southern Kyushu would have been reinforced by two combat divisions, along with the corresponding number of base and service troops…"
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looks at another D-Day: German set for Flames of War.