“It was suppose to be only 6 megatons or twice as big as Hiroshima.”
Little Boy, the Hiroshima bomb was nowhere near that powerful. It’s estimated it was about .013 to.018 of one megaton. The most powerful nuke in our arsenal today is about 1.2 megatons.
https://en.wikipedia.org/wiki/Nuclear_weapon_yield
Okay and thanks.