You and
@tsubaki might know about this. I understand why the first bomb was dropped after the fierce defence of the Japanese islands but why was the second bomb dropped on Nagasaki?
Like
@tsubaki said, they hadn't surrendered and that's even after an amendment to the Potsdam declaration for unconditional surrender to allow the Emperor to stay.
They actually saw the amendment, which was there to stop them being nuked, as an act of weakness and the Supreme War Council wanted to keep fighting on.
You had the Kyujo incident, like
@tsubaki also mentioned, where the coup failed because they couldn't find the tape.
General Anami (War Minister) and General Umezu (Chief of Army) were pretty much hell bent on fighting on, with the Second Army (key to defence) in Hiroshima.
Unknown to them, we (well the Yanks) had no more weapons after that and it would have took a while to produce some more, so thank God they did surrender.
@degsy the first weapon (Little Boy) was a uranium weapon with a gun-type trigger, whereas Fat was plutonium (made from uranium-238) with an implosion mech.