For what its worth, my understanding is that American POW's imprisoned at the Fukuoka 14 Prison Camp doing slave labor witnessed the Nagasaki bomb delivery. They felt the heat and experienced some of the blast wave. The bomb signaled that their daily beatings and random executions would end within days. A couple of years ago, one POW survivor published the book "Nagasaki Saved My Life: How One POW Survived Burma's Death Railway, Japanese Hell Ships, And The Atom Bomb". Look it up.
Wes
N78PS
There were some American POWs in Hiroshima who were killed by the bomb, I think. I don't have the book with me right now, but I think it is in the Enola Gay book, which is a good one to read.