However, despite devastating bombing of Japan's cities and the nearly total strangulation of her imported supplies, neither the Emperor or his government were willing to surrender. They were fully prepared for a suicidal attack on invading allied forces with whatever they could put together. Though they could not have more than slowed an allied invasion in the fall of 1945, they would have continued a guerrilla war against occupying forces for years. Allied POW's also would have been automatically killed once the invasion started.
What Truman hoped to accomplish was a knockout punch that would move the idea of surrender forward. The dropping of the second bomb was done simply because it was ready and the Japanese government had nor responded in time. The idea of using it as a "test" is absurd--the device had already been tested on New Mexico in July 1945. The Hiroshima bomb was the untested one.
So much for revisionist history.
The "test" some people wanted, mostly scientists at Los Alamos and Oak Ridge, was to explode the bomb off the coast of Japan in order to demonstrate the power of the bomb without killing people. Since we only had enough Uranium-235 for one bomb (Little Boy) and enough Plutonium for three "Fat Man" style bombs (although Hanford was producing enough were by late Sept. we could have 3 or 4 bombs per month) it was decided not to offer a demonstration.
The theory behind the Uranium gun weapon (Little Boy) was so simple the scientists knew it would work without testing. They had to test the plutonium bomb in order to make sure it worked. This left the U.S. with enough plutonium for more bombs. One was Fat Man which detonated over Nagasaki with a yield of 20-22 kilotons. Col. Tibbets had sent several B-29's back to the U.S. after Nagasaki in order to pick up the next bomb but Gen. Groves halted the shipment to see if the Japanese would surrender.
the device had already been tested on New Mexico in July 1945.
And I took the tour of Trinity just last month. For a historian who has focused on atomic history, it was a blast. No pun intended. LOL