Editing Operation Downfall (section)

===Ground threat===
Through April, May, and June, Allied intelligence followed the buildup of Japanese ground forces, including five divisions added to Kyūshū, with great interest, but also some complacency, still projecting that in November the total for Kyūshū would be about 350,000 servicemen. That changed in July, with the discovery of four new divisions and indications of more to come. By August, the count was up to 600,000, and [[Magic (cryptography)|Magic cryptanalysis]] had identified nine divisions in southern Kyūshū—three times the expected number and still a serious underestimate of the actual Japanese strength.

Estimated troop strength in early July was 350,000,{{r|MacEachin p16}} rising to 545,000 in early August.{{r|MacEachin p18}}

{{blockquote|The intelligence revelations about Japanese preparations on Kyushu emerging in mid-July transmitted powerful shock waves both in the Pacific and in Washington. On 29 July, MacArthur's intelligence chief, [[Charles A. Willoughby|Major General Charles A. Willoughby]], was the first to note that the April estimate allowed for the Japanese capability to deploy six divisions on Kyushu, with the potential to deploy ten. "These [six] divisions have since made their appearance, as predicted," he observed, "and the end is not in sight." If not checked, this threatened "to grow to [the] point where we attack on a ratio of one (1) to one (1) which is not the recipe for victory."{{sfn|Frank|p= 211|loc= Willoughby's Amendment 1 to "G-2 Estimate of the Enemy Situation with Respect to Kyushu"}}}}

By the time of surrender, the Japanese had over 735,000 military personnel either in position or in various stages of deployment on Kyushu alone.{{sfn|Giangreco|2009|loc=Appendix B.}} The total strength of the Japanese military in the Home Islands amounted to 4,335,500, of whom 2,372,700 were in the Army and 1,962,800 in the Navy.<ref>[http://www.geocities.co.jp/WallStreet/2687/siryo/siryo16.html Ministry of Health and Welfare, 1964.] {{Webarchive|url=https://web.archive.org/web/20160105112919/http://www.geocities.co.jp/WallStreet/2687/siryo/siryo16.html |date=January 5, 2016 }} Retrieved July 21, 2015.</ref> The buildup of Japanese troops on Kyūshū led American war planners, most importantly General George Marshall, to consider drastic changes to Olympic, or replacing it with a different invasion plan.{{citation needed|date=October 2009}}