GEOFF BENNETT: Eighty years ago this week, the U.S. altered the course of history when, for the first time ever, it dropped the extraordinarily powerful atomic bomb on Japan.

It ultimately led to the end of World War II.

The motivation and secrecy surrounding the development of that world-changing weapon and the devastating consequences of its use are the focus of a new oral history out today from author Garrett Graff.

He recently sat down with Amna Nawaz to discuss his book "The Devil Reached Toward the Sky."

AMNA NAWAZ: Garrett Graff, welcome back to the "News Hour."

Thanks for being here.

GARRETT GRAFF, Author, "The Devil Reached Toward the Sky": Thanks for having me.

AMNA NAWAZ: So you have compiled these incredible oral histories for some of the biggest moments in world history, D-Day, 9/11.

Why did you want to apply that approach to this, to the making and actual deployment of the first atomic bomb?

GARRETT GRAFF: Yes.

August, of course, marks the 80th anniversary of the bombing of Hiroshima, the bombing of Nagasaki, the end of World War II.

And so this is a moment where we have, effectively, every first-person memory of the atomic bomb we're ever going to have.

And so this is trying to sort of tell the story of the Manhattan Project through the eyes of the scientists at a moment when they don't know who's going to win World War II yet.

They don't know whether Adolf Hitler is going to get the first atomic bomb.

They don't even know whether an atomic bomb will work.

AMNA NAWAZ: And you do begin with the accounts and the stories of many of those scientists in Germany and in other nations, Albert Einstein, as you mentioned.

Even Sigmund Freud is quoted in there in the early 1930s.

They're commenting on the rise of Adolf Hitler in that moment.

Why start with that?

Why are their voices... (CROSSTALK) GARRETT GRAFF: Yes.

When we talk about the atomic bomb today, we instantly think of Japan.

We think of the war in the Pacific.

But understanding the roots of the Manhattan Project, it's all about the war in Europe.

It's about these mostly Jewish refugee scientists fleeing the enveloping cloak of fascism in Europe, coming to the United States and desperately trying to get the attention of the U.S. government and the U.S. military to launch a all-hands-on-deck atomic bomb effort because they are afraid Adolf Hitler will get the bomb first.

AMNA NAWAZ: Of course, for anyone who saw the movie, the role of Robert Oppenheimer is no surprise in this, but you write that the choice of Oppenheimer to lead this effort would come to define the Manhattan Project in so many ways.

Why and how?

GARRETT GRAFF: We too often think that the whole thing is Oppenheimer and Los Alamos, but the weight of the Manhattan Project really takes place in places like Oak Ridge, Tennessee, and Hanford, Washington where we build these 100,000-person cities, secret cities, where we refine and manufacture uranium and plutonium at the scale of kilograms with work forces who don't know what they're doing, don't know how they're contributing to the war effort in these incredibly secret communities and factories.

AMNA NAWAZ: This is another part that fascinates me.

For the scale and scope of this project, these multiple locations, as you mentioned, for all the folks that are pulled together in this, including Oppenheimer, his wife, Katherine, so many others, the secrecy under which they had to work, there are literally signs posted in all the places that they work saying they can't say anything any time they leave the grounds.

How did such an enormous undertaking remain a secret?

GARRETT GRAFF: Yes, it has a lot to say about wartime patriotism.

It has a lot to say about how hard it was for information to travel, for news to travel in that pre-Internet era.

But a lot of it is also just need to know.

There's this fabulous part of the story where in Oak Ridge at those uranium plants, much of the work is actually done by these sort of high school girls that Tennessee Eastman, the company that's running the plant... AMNA NAWAZ: They're all local high school girls they hire to work there, right?

GARRETT GRAFF: They're all -- exactly.

This is who you can hire in '43 and '44 in America.

And they run these Calutron, these machines, and most of them learned the word uranium for the first time on August 6, 1945, when Harry Truman announces the existence of the Manhattan Project.

AMNA NAWAZ: There's a major shift, of course, when Hitler dies by suicide in April of 1945.

As you mentioned, Hitler had been the primary justification for that atomic bomb work for so many and those scientists.

You quote one, Emilio Segre, who's an Italian-American nuclear physicist, who says: "Now that the bomb could not be used against the Nazis, doubts arose.

Those doubts were discussed in many private conversations."

What were those doubts, and how does the target shift to Japan?

GARRETT GRAFF: What's so striking in the memories of the scientists who were working on it was a lot of them are sad that their work is too late, that they wish that the bomb had been ready early enough to drop on Berlin.

And it's only in those final months of the war, when Germany has already defeated or on its way to defeat, that they sort of wrap their heads around, oh, this is actually going to be used in Japan.

And that's when their doubts arise, because they -- again, these are European, mostly Jewish, refugee scientists, and a lot of them say, hey, we signed up to build a bomb to stop Hitler.

We don't want this thing used on Japan.

Like, that's not the fight that we intended to have here.

AMNA NAWAZ: After the bombings -- and you go into incredibly fascinating detail about the B-29 squadron that's pulled together to pull this off -- after the bombings, some of the most haunting things in the book are the recollections of the children in Japan, what they saw and what they remember from that day, some 5, 6, 7 years old,.

There's a ninth grader, you quote, in there who says: "It was like being thrown into an iron melting pot.

My face burned.

I jumped into the river.

One of my friends found me and asked how his face looked.

The skin was hanging down from his face like a rag.

I was too scared to ask him about my own face," just horrific descriptions of what unfolded on the ground.

Did the general American public know about the impact of the bombs?

Did they support it at the time?

GARRETT GRAFF: Yes, those final chapters are just this incredible juxtaposition of the triumph of the Manhattan Project workers, the bomber crews, the Enola Gay, which delivers the bomb to Hiroshima.

They land.

They get medals pinned on their chest, and then they go off to a literal barbecue party to celebrate the bombing, while Hiroshima burns behind them.

And the reality of that bomb was kept from the American public and kept from the Japanese public actually for years.

And it's really only through the work of journalists like John Hersey writing for "The New Yorker" in the summer of 1946 who bring that full picture back to the American people for the first time.

AMNA NAWAZ: The very last quote is from Albert Einstein.

And you quote him as saying: "I don't know how the Third World War will be fought, but I can tell you what they will use in the fourth, rocks."

In looking back at the use of the atomic bomb, do you feel like you learned anything about where we are now or what the potential is for the use of a nuclear bomb now?

GARRETT GRAFF: Yes.

This year we have already seen conflict between India and Pakistan, the two largest nuclear arsenals in the world to ever come into direct conflict.

We have seen the U.S. and Israeli strikes on the Iranian nuclear program.

We're seeing the U.S. geopolitical instability prompt conversations about proliferation in Europe and Asia and countries like Korea, even some conversations in Japan, which was sort of once unthinkable.

And I think, for me, those searing survivor testimonies, one of the reasons I wanted to sort of tell that story right now, as that generation passes, is that I think we need to, as a society, as a country, as a people, recommit ourselves in this moment, where I think we're actually going to see more countries joining the nuclear club over the next decade, to fulfill the vision of those hibakusha, the survivors, that they be the last survivors of a nuclear weapon in our age.

AMNA NAWAZ: The book is "The Devil Reached Toward the Sky: An Oral History of the Making and Unleashing of the Atomic Bomb."

The author is Garrett Graff.

Garrett, always great to see you here.

Thank you so much.

GARRETT GRAFF: Thanks for having me.