The bomb
From Antipixel:

He'd been taken prisoner somewhere in the Pacific (can't recall where) and was being held with other POWs in the hold of a old freighter moored in Nagasaki harbour.

They were kept in the bottom of the ship, below the waterline, and he said that when the bomb went off they heard it and then the sides of the hold became too hot to touch.

Jesus. That might be the best weblog entry I've ever read.