Author's note: This is the first installment of my personal memoir of the nuclear era, The American Doomsday Machine. This online book, being published on Truthdig and other sites, will recount highlights of my six years of research and consulting for the Departments of Defense and State and the White House on issues of nuclear command and control, nuclear war planning and nuclear crises. It further draws on 34 subsequent years of research and activism largely on nuclear policy, which followed the intervening 11 years of my preoccupation with the Vietnam War.

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One day in the spring of 1961, soon after my 30th birthday, I was shown how our world would end. Not the Earth, not -- so far as I knew then -- all humanity or life, but the destruction of most cities and people in the Northern Hemisphere.

What I was handed, in a White House office, was a single sheet of paper with some numbers and lines on it. It was headed "Top Secret -- Sensitive"; under that, "For the President's Eyes Only."

Long after the ending of the Cold War, the chance that some nuclear weapons will kill masses of innocent humans somewhere, before very long, may well be higher than it was before the fall of the Berlin Wall.

One phase of the Nuclear Age, the period of superpower arms race and confrontation, has indeed come to a close (though the possibility of all-out, omnicidal exchange of alert forces triggered by a false alarm remains, inexcusably, well above zero). But another dangerous phase now looms, the era of nuclear proliferation and with it, an increased likelihood of regional nuclear wars, accidents, and nuclear terrorism. And the latter prospect is posed not just by “rogue” states or sub-state terrorists but by the United States, which has both led by example for 60 years of making nuclear first-use threats that amount to terrorism and may well be the first or among the first to carry out such threats.

Averting catastrophe -- not only the spread of weapons but their lethal use -- will require major shifts in attitude and policy in every one of the nuclear weapon states, declared and undeclared. But such change is undoubtedly most needed, and must come first, in the United States and Russia.

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.

It was in a ninth-grade social studies class in the fall of 1944. I was 13, a boarding student on full scholarship at Cranbrook, a private school in Bloomfield Hills, Mich. Our teacher, Bradley Patterson, was discussing a concept that was familiar then in sociology, William F. Ogburn's notion of "cultural lag."