It was a hot August day in Detroit. I was standing on a street corner downtown, looking at the front page of The Detroit News in a news rack. I remember a streetcar rattling by on the tracks as I read the headline: A single American bomb had destroyed a Japanese city. My first thought was that I knew exactly what that bomb was. It was the U-235 bomb we had discussed in school and written papers about, the previous fall.

I thought: "We got it first. And we used it. On a city."

I had a sense of dread, a feeling that something very ominous for humanity had just happened. A feeling, new to me as an American, at 14, that my country might have made a terrible mistake. I was glad when the war ended nine days later, but it didn't make me think that my first reaction on Aug. 6 was wrong.

Unlike nearly everyone else outside the Manhattan Project, my first awareness of the challenges of the nuclear era had occurred—and my attitudes toward the advent of nuclear weaponry had formed—some nine months earlier than those headlines, and in a crucially different context.