I think there was also the shock effect of this one tiny bomb with that much power. And the Japanese didn't know that America only had those two available. They

I think there was also the shock effect of this one tiny bomb with that much power. And the Japanese didn't know that America only had those two available. They could have had thousands for all they knew. And this is also something that could strike their leadership. You can build bunkers against conventional bombs but for nuclear that's a different ball game