I was a member of a group that was led by Niels Bohr, after the test in Alamogordo, that was very much opposed to the use of this new weapon on civilian cities. … But by and large we were in a minority, but a rather distinguished minority. But the trouble was that this second memorandum to Roosevelt went off to him, but he never read it, he died before he read it. And Truman, of course, was a different kettle of fish.

On efforts to avoid civilian deaths in the first uses of atomic weapons, p. 32 - Portraits in Science interviews (1994)