If you have never read it, I high recommend "The Atomic Bombings of Hiroshima & Nagasaki" by the Manhatten Project [1].

There are some facinating technical details (in particluar the way heat reflected in the hills of Nagasaki) but in general it makes for grim reading.

I was always struck by the contrast between the dispassionate analysis in the report and the final eye witness account in the appendix.

I always had the feeling that they knew what they had done and knew that it was wrong.

[1] https://www.abomb1.org/hiroshim/hiro_med.pdf