William Brangham:

Christopher Nolan's upcoming film "Oppenheimer" tells the story of the brilliant physicist and his intense work to develop the weapons that would help America win the Second World War.

Two of the bombs he and his colleagues helped create were dropped on Japan, killing several hundred thousand people, mostly civilians, but helping bring the war to a quicker end. Afterwards, Oppenheimer expressed regret about these weapons and worked to stop their proliferation.

In 1954, at the height of anti-Soviet fervor, his security clearance was revoked over allegations that he had ties to communism. But almost 70 years later, long after his death, Energy Secretary Jennifer Granholm reversed that decision, saying: "As time has passed, more evidence has come to light of the bias and unfairness of the process that Dr. Oppenheimer was subjected to, while the evidence of his loyalty and love of country have only been further affirmed."

For more on this complicated man and his role in history, I'm joined now by Alex Wellerstein. He's a historian of nuclear weapons, a professor at the Stevens Institute of Technology, and author of "Restricted Data: The History of Nuclear Secrecy in the United States."

Professor Wellerstein, great to have you on the "NewsHour."

For those of us who are not familiar with Oppenheimer's work on the Manhattan Project, can you just remind us a bit of what role he played and how central he was to that?

Alex Wellerstein, Author, "Restricted Data": Oppenheimer was the scientific director of the Manhattan Project and the director of the Los Alamos Laboratory.

And so, in this position, he was in charge of all of the scientific decision-making, all of the advising on the production of the bombs, crucial to the planning for the actual use of the bombs, and was credited as sort of the glue that held together this massive, sprawling new industry that had been built in unprecedented time in total secrecy during World War II.

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