The military, knowing how tough the battling was on Iwo Jima and Okinawa, didn't want to shed thousands more troops on mainland Japan, so Truman gave the greenlight to bomb Hiroshima and Nagasaki, while the US could have delayed an actual invasion of mainland Japan for several days, it did mean more fighting in the meantime. The first detonation was definitely warranted, although, if I were the president at the time, I would have insisted that they drop the first bomb on the largest military command that was still functioning and wait. Then, if after two weeks, no word of surrender came, I'd have given the word to drop it on Tokyo to get their attention.Whatever labored, embarrassing arguments one can make for the nuking of Hiroshima cannot be made for the nuking of Nagasaki just three days later. From my article "Did We Really Need to Use the Atomic Bomb Against Japan?":
On August 9, 1945, just three days after we nuked Hiroshima, and before Japan’s leaders had sufficient time to process and respond to our nuclear attack on Hiroshima, we dropped an atomic bomb on the city of Nagasaki, which was home to Japan’s largest Christian population. The atomic bombing of Nagasaki was even more inexcusable than the nuking of Hiroshima. . . .On August 9, we nuked Nagasaki, just three days after Hiroshima, and hours after the Soviets began to maul the Japanese army in Manchuria,, and while Japan’s civilian leaders were understandably absorbed with trying to process what had happened to Hiroshima and with responding to the Soviet attack in Manchuria. Surely Truman and other high officials knew that three days was not enough time for Japan’s government to formulate a formal response to the unprecedented use of the atomic bomb on Hiroshima and to the Soviet invasion in Manchuria. Even McGeorge Bundy, who helped Henry Stimson write his defense of the atomic bombing of Japan, acknowledged that Truman was too quick to nuke Nagasaki:
"It is hard to see that much could have been lost if there had been more time between the two bombs. . . . Such a delay would have been relatively easy, and I think right." (https://miketgriffith.com/files/immoraluse.pdf)The Japanese were not even able to get a scientific team to Hiroshima until August 7, the day after the attack. Meanwhile, Japan's leaders were getting conflicting, fragmentary information about what had happened in Hiroshima. Some Army officials were telling the government that the bombing of Hiroshima was merely a very large conventional bombing raid, and they were suppressing information about the kinds of wounds that had been inflicted. There was no Internet back then, no fax machines, no Skype.
Surely it was obscene for us to nuke Nagasaki just three days, 72 hours, after we had nuked Hiroshima.