On August 6, 1945, the United States dropped an atomic bomb on the Japanese city of Nagasaki. The bombing caused cataclysmic destruction to the city and killed an estimated 40,000 people. Among those in Nagasaki were hundreds of Allied prisoners of war. Now we can read the stories of some of those survivors in their own words. Author John Willis included notes, diaries and memoirs of the Allies who witnessed the attack in his new book "Nagasaki: The Forgotten Prisoners." Willis joined GBH All Things Considered host Arun Rath to discuss those survivors' stories. This transcript has been lightly edited.

Arun Rath: So first, give us a sense of this group of prisoners. It was a fairly diverse group of people, right?

Willis: Yes, it was. There were British, Dutch, Australian and some Americans as well — so it was quite a mixed bag — and there were two camps in Nagasaki. One was very close to what turned out to be the detonation point of the atomic bomb, and one was a little further away.

Rath: And I have to imagine they would have arrived in Nagasaki from diverse paths, as well.

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Willis: Well, I think that Nagasaki was just the end of their endurance test. They'd already been captured in places like Java and Singapore, housed in pretty brutal conditions in those countries. Many had worked on the Thai-Burma railway, the place where they built the famous Bridge on the River Kwai.

And then they were transported to Nagasaki on what were called "hell ships," which were basically rusty old hulks that were 20 or 30 years old and had hundreds or, indeed, sometimes thousands of prisoners crammed so tightly in the holds that they couldn't lie down, they just had to sit up because it was so full of people.

Rath: Now, as you're describing, Imperial Japan was notorious for its brutal treatment of prisoners of war. There was abuse, torture, slave labor. How did things in Nagasaki — which was the end of the line, as you're describing it for these men — how did things there compare?

Willis: I think that for some of them, having survived the "hell ships" and having worked in the jungles alongside the River Kwai, Nagasaki — to a certain extent — was a relief. It was a big city, quite European. But the work there was very hard. They were basically driving the Japanese military industrial machine, and they weren't at all well-treated. Food was meager. There were lots of cases of people catching pneumonia, but no medicine was provided. So I think in both camps, over 100 people died of pneumonia during this period. So Nagasaki, although it was in one way a relief, for most of us it would still be a pretty bleak place to work and to live under Japanese rule.

Rath: And as we're getting up to this period in August of 1945, it's at a time when mainland Japan is being bombed quite extensively by the United States at that point. What was their sense of what was going on in the war at that time?

Willis: I think they picked up fragments of information. One or two guards or locals might say a few things. They might pick up a little bit of a Japanese newspaper. There were no radios in the camps in Nagasaki, it was just too dangerous. They vaguely knew the war in Europe was over. I think their first clue that things were changing was when they started to hear U.S. bombers coming overhead, and Tokyo and Osaka and other major Japanese cities were firebombed in the spring of 1945. But it wasn't until later on, in the summer, August the first, that Nagasaki started to be bombed with conventional bombs. And I think that was the moment they started to think "This might be our route out of here."

Rath: Any word come around of what had happened days earlier at Hiroshima?

Willis: They had absolutely no idea. They had no idea [what happened in] Hiroshima. Most of them had probably never heard of it. They certainly didn't know an atomic bomb been dropped on it. And they had no idea what an atomic bomb was. It was something that was just completely and totally unknown to them. And so when the bomb dropped and the city was swept aside — as if by a broom, as one of them said — they just didn't know. They thought maybe this is the end of the world.

Rath: You mentioned there were two camps. So where were the men distributed when the bomb was dropped over Nagasaki?

Willis: Well, in the camp that was just over a mile from the detonation point, they were really lucky. There were nearly 200 prisoners there and only eight of them were killed because they were mainly inside buildings. And outside where, in the open air as it were, ordinary Japanese civilians on the same radius from the detonation point died in very large numbers. So they're extremely lucky.

The second camp, which is actually where the Americans were, was about 4 or 5 miles away from the detonation point. They lost all the windows, roofs were blown off, they were blown off their feet. But they survived. And the bomb has actually been dropped not at the designated target, because they were running out of fuel. And if they'd have dropped it where it should have been dropped, then that second camp, the one with the Americans in it, would have been destroyed.

Rath: And tell us a bit more of what they experienced immediately and in the aftermath.

Willis: They woke. Quite a lot of them were knocked out by flying bricks or roofs, but they emerged from it. And the camp that had been there with its barracks and guardsroom and cookhouse and everything else was just completely flattened. There was smoke, dust. And then one of them describes seeing about a hundred Japanese civilians running past him like wild animals trying to escape from the hunt. And they had, you know, blistered arms and what he described as "wind-torn pennants." And they just ran and ran and ran and didn't even look at him. Others saw shadows in concrete where people had been standing when the bomb dropped and they were just now shadows. There were obviously lots of dead bodies. So they all ran up to the hills and looked down on this scene of utter devastation, just an old skeleton of a building. And some Australians just piled onto the the cart, including the wounded. The several of them said, "I thought I was dead. I thought this was the end of the world."

Rath: These men who have been through hell, multiple hells, they're already so traumatized. How did this stay with them in various ways after the fact. I mean, it's almost PTSD that I can't even imagine.

Willis: When they arrived back to the various countries, people didn't really know how to treat them, and they didn't really know how much they should talk about it. They didn't really want to frighten their their families or their friends. And but, of course, they were physically very different. They were thin, under 100 pounds. They continued to have lots of malaria, there were cases of people having malaria for 40 or 50 times. And of course, they were deeply disturbed. All prisoners of war in Japanese hands were disturbed, but obviously those who went to Nagasaki had the most brutal of experiences. And lots of them had nightmares. Quite a lot of them found it really difficult to manage their relationships with their fiancées or wives when they got home. Some didn't really know how to deal with their kids and the children not know who was this man suddenly coming through the door, and people calling him "Daddy: and I've never met him before? And so it was extremely difficult to to manage.

And one of the prisoners whose son I spoke to quite a lot when writing the book said the tragic thing was that he survived the war and all these endurance tests, but he lost the peace. When he got home, he was just never a happy man. He was just never settled, never happily married and just always unhappy. So I think it was difficult. It wasn't over that day, on the 9th of August — that was a beginning, in a way, of another chapter.

Rath: John, this is amazing stories and it's been great talking with you. Thank you.

Willis: Thank you.

Rath: John Willis is one of Britain's most distinguished television executives. He's a former director of programs at Channel 4 and director of factual and learning at the BBC. He was vice president of national programs at GBH Boston when we were WGBH. His new book, "Nagasaki: The Forgotten Prisoners," is out now. This is GBH is All Things Considered.