What were Truman's options and why did he drop the atomic bomb?

Answer 1

Truman did not just "drop the atomic bomb", he had the Army, Navy, and Marines simultaneously preparing every single option available for destroying Japan's military ability to continue the war. Some of these were already in process, some of them were on the verge of being used, some of them would take significant time to prepare before they could be used.

1. The Army Air Forces were already carrying out multiple nightly 1000 plane firebombing raids, each of these firebombing raids did as much damage and killed as many people as one of the atomic bombs did.
2. The Army Corp. of Engineers Manhattan Project had plans and facilities to produce 23 atomic bombs by the end of 1945 (and many more in 1946, 1947, etc. if necessary). The first 2 of these became available in August and were used on August 6 and August 9. A 3rd had been manufactured before the Japanese surrender and could have been used sometime in late August.
3. The US and USSR had agreed that the Soviets would declare war on Japan in the middle of August and attack both Manchuria and the far northern islands of Japan. The Soviets actually accelerated this after the atomic bombing.
4. The Navy, Marines, and Army were planning and making preparations for a massive D-day invasion (bigger than the 1944 Normandy D-day invasion) of southern Japan in late October or early November of 1945.
5. Large stockpiles of chemical weapons (e.g. nerve gas, mustard gas) were being prepared for use during the invasions of Japan.
6. The Navy, Marines, and Army were planning and making preparations for a massive D-day invasion (bigger than the 1944 Normandy D-day invasion) of northern Japan in the spring of 1946.

The surrender of Japan after the 2nd atomic bomb caused Truman to cancel the orders for all of these various military options that were already in process and needed no authorization, approval, or further orders from anyone (and would have been automatically carried out as ordered, had Truman not canceled them).

The reason any and all of these options were being used or being prepared to be used was simple: it was believed that Japan would "fight to the last man" and unless their military ability to continue the war was completely destroyed the war in the pacific was not going to end. It seemed likely that this might require a 90% or larger fatality rate of the Japanese and the US was both willing and prepared to do that if it was actually necessary! Every single option and means to do this was in use by Truman!