[NVSmith]

-These comments are in the "for what it's worth" category. I'm retired Army & have been studying Operation Downfall, the invasion of Japan proper, since the big kerfluffle over exhibiting the "Enola Gay" at the Smithsonian. I have a number of books and articles on the subject and have done research at the National Archives, the Army Historical Center and the Marine Corps Library & Historical Center at Quantico, VA. I have virtually the entire Allied and Japanese orders of battle. The Allied fleet dwarfs June 6, 1944.
-First, there were political reasons to end the war quickly. With the war in Europe over and soldiers being discharged on “points” the thought of at least another year in combat, with the possibility of 500 thousand to 1 million casualties was not something either politicians or the public wanted to think about. The casualties at Iwo Jima and Okinawa frightened the crap out of a lot of policy makers, particularly with the heavy presence of Kamikazes at Okinawa.
-Second, there were some alternative weapons that hadn’t been used. (A) The 22nd Air Force was finally convinced (read “ordered”) to start an anti-ship mining campaign. By 1945 most of the remaining Japanese merchant marine was hugging the coastline where US submarines couldn’t safely operate but mines were effective. (B) The Army Chemical Warfare Service developed and published a Top Secret plan to use poison gas against the Japanese. A copy of the plan was uncovered a few years back, declassified and published in Military History Quarterly magazine. (C) In addition to measures listed by previous commentators, there were plans to spray plant killers and petroleum products on rice paddies as planting season began; it was hoped to eliminate up to 80% of the domestic rice harvest.
-Third, the largest organized Japanese military force remained virtually intact in Manchuria. That force, combined with whatever troops might be pulled out of China, would add at least an order of magnitude to Japanese defenses if they could be brought to the Home Islands.
-By the way, the Japanese high command knew EXACTLY where we were going to attack and even had a reasonable estimate of the timeline. In contrast, the US high command completely underestimated Japanese home defense/civil defense plans and capabilities. The Japanese had thousands more suicide vehicles than we estimated including weapons we knew nothing about and hidden fuel reserves for operations.
-The bombs brought the war to an end, partially because the Japanese had no idea how many more bombs we had; we still had the capability to invade and the Soviet Union had just entered the war, opening a new front.
-Many, but not all, Japanese historians believe that the bombing saved countless Japanese (and American) lives while retaining at least some infrastructure that could be used for rebuilding.
-There are other issues to consider, including one that very few historians have considered. If anyone is interested in further flagellating this deceased equine, let me know and I’ll post some more.