At Iwo Jima, Okinawa, and other island bases of the Japanese forces, the Japanese created a network of deep tunnels and bunkers that made US attempts to evict Japanese forces extremely difficult, time consuming and expensive in terms of loss of lives. Based on these experiences, U.S. military planners anticipated that the human cost of invading Japan would be severe. See Giangreco, D.M., "Casualty Projections for the U.S. Invasion of Japan, 1945-1946: Planning and Policy Implications," Journal of Military History, 61 (July 1997), pp. 521-582, at pp. 534-35.

Given that MacArthur planned an amphibious assault against the Japanese homeland at Kyushu, an obvious choice that the Japanese expected, did the Japanese create defense positions similar to those at Iwo Jima at Kyushu, and if so, when did they begin work how much progress had they made on these defenses by the time the atomic bomb was dropped on Hiroshima?

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    I would upvote if the assertions in the first paragraph were linked to resources. This is an great example of a question that can educate even if it is never answered. – Mark C. Wallace Aug 22 '14 at 18:22
  • @MarkC.Wallace See the source I provided. Interesting reading, too. – Bruce James Aug 22 '14 at 20:26
  • It is maybe better if you compare the situation to Okinawa and not to Iwo Jima. Iwo Jima is a small, uninhibited island with extreme number of soldiers. Okinawa is an inhibited island. At the Battle of Okinawa the effectiveness of Japanese defense was much weaker, and the big part of casualties are civilians who got caught between the two armies. – Greg Oct 23 '14 at 7:42
  • @Greg Indeed, the Okinawa invasion was relatively smooth on the most part, in spite of heavy kamikaze efforts and tunnel system. However Kyushu cannot even compared to Okinawa: it is an island of several hundreds kilometer long, which means thousand of kilometer seashore. Even in Okinawa landing meant landing on all shores. Landing Kyushu is very much like the D-day and Germany's problem: no-one knows for sure where the invasion force will come, and it is impossible to build an effective defense line hundreds kilometers long. – Greg Jan 17 '15 at 17:14

The standard Japanese defense plan was in place for opposing Olympic. While the bunkers might not have the complexity of Iwo Jima's due to different geology on Kyushu, they would have been tough enough.

The two aspects that were being explored that were unique to this invasion was the planning to deploy small Tokko boats (Kamikaze boats with explosives) to attack not the large ships, but the landing craft loaded with troops. There were also plans to use civilians to carry bombs to attack US troops. Even if these had only a marginal military effect, the human cost on the soldiers to be forced to shoot down civilians would have been large, and the loss to the Japanese civilians would have been large.

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  • Can you provide sources? – Bruce James Aug 22 '14 at 19:58
  • Strategy & Tactics Magazine #45 with Operation Olympic, the Invasion of Japan 1945, Simulations Publications, Inc 1st Edition – Oldcat Aug 22 '14 at 20:27
  • Often overlooked in discussion of the planned Japanese invasion is that the United States intended to drop atomic bombs (I believe 3 were considered) just before the invasion forces started their landing operations (see the Wikipedia article on Operation Downfall). This could easily have ended the war right then and there as Japanese soldiers were certainly not ready to defend against the atomic bomb. – Barry Aug 23 '14 at 1:38
  • Barry. That is incorrect. there were no more atomic bombs, at least not for another 9 months. One of the reasons why the two bombs were dropped just 3 days apart was, the US wanted to give the impression that there was a lot more where that came from. Had the japanese known the US was out of bombs, they would probably have fought on. – sofa general Dec 5 '18 at 17:15

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