On the Anniversary of the First Use of Nuclear Weapons
It is important to appreciate that the Japanese nuclear physicists got samples of the dust, and determined that Little Boy was a Uranium-235 bomb. They had their own nuclear program, and knew that Uranium 235 is hard to separate from U-238. They reported to the cabinet that this was a catastrophe, but would not happen again. The Japanese cabinet decided to continue the war, with the intent of accepting 30 million Japanese deaths if that was necessary to cause 1 million US deaths. They were sure that the US would not accept that many casualties. They were certain that they would be able to force the US to negotiate with them.
Fat Man, dropped later on Nagasaki was a plutonium bomb, as shown by analysis of the dust. The Japanese physicists knew that plutonium could be chemically separated from Uranium 238, and mass production of nuclear bombs must be anticipated.
The US knew the Japanese strategy, due to masterful decryption efforts, grouped under the code name MAGIC. Fat Man saved a million US lives, and 30 million Japanese lives. It also prevented Soviet occupation of part of Japan.