- J. Robert Oppenheimer: [on the proposal for talks to halt the spread of nuclear weapons] It's twenty years too late. It should have been done the day after Trinity.
- Frank Oppenheimer: [on Hiroshima] The first reaction was, "Thank God it wasn't a dud." But before the whole sentence of that broadcast was finished, one suddenly got this horror of all the people that had been killed. And I don't know why - up to then I don't think I'd really thought of all those flattened people. We talked often about having a demonstration where there weren't people. Maybe on the mainland so that the military would see it, but where there weren't people. And then the thought that they had actually dropped it on a place where all those people were and the image of those people, which came before any pictures of it, really was pretty awful. But the first thing was, I'm sure, "Thank God it worked."
- Frank Oppenheimer: [on Trinity] I wish I could remember what my brother said, but I can't. But I think we just said "It worked." I think that's what we said, both of us. "It worked."
- Haakon Chevalier: Stinson Beach, California. August 7th, 1945. Dear Oppie, you're probably the most famous man in the world today, and yet I am not sure that this letter will reach you. But if it does, I want you to know that we are very proud of you. And if it doesn't, you will know it anyway. We have been irritated by your reticence these past few years, but under the itchy surface we knew that it was all right. The work was progressing, but the heart was still there, and the warm being we have known and cherished. I can understand now, as I could guess then, the somber note in you during our last meetings. There is a weight in such adventure, which few men in history have had to bear. I know that with your love of men, it is no light thing to have had a part, and a great part, in a diabolical contrivance for destroying them. But in the possibilities of death are also the possibilities of life. You have made history. We are happy for you.