The recent false alarm in Hawaii is a stark reminder of how on edge the world is over fears of a nuclear attack. Many national security experts warn the world is at higher risk of a nuclear-armed conflict today than during the Cold War. North Korea’s nuclear capabilities have progressed quicker than many expected. The Iranian nuclear agreement is at risk of crumbling. India and Pakistan have weapons pointed at each other. Israel’s stockpile of an estimated 80 nuclear weapons add to tensions in the Middle East. And the U.S. and Russia, with close to 14,000 weapons between them, are embroiled in renewed political tensions.

Few people know the complexities of nuclear proliferation like Daniel Ellsberg, who worked as a strategic analyst at the RAND Corporation, focused on control of nuclear weapons. It was during his time at RAND that Ellsberg leaked the Pentagon Papers in 1971, setting off a debate about the U.S.’ role in the ongoing war in Vietnam. While he remains an activist and a supporter of whistleblowers, Ellsberg has turned his attention back on the weapons that continue to threaten the future of humanity through in his new book The Doomsday Machine: Confessions of the Nuclear War Planner.

Daniel Ellsberg: One day in the spring of 1961, soon after my thirtieth birthday, I was shown how our world would end. Not the earth itself, not—so far as I knew then, mistakenly—nearly all humanity or life on the planet, 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 a simple graph on it. It was headed “Top Secret—Sensitive.” Under that was “For the President’s Eyes Only.”

The “eyes only” designation meant that, in principle, it was to be seen and read only by the person to whom it was explicitly addressed—in this case, the president. In practice, it usually meant that it was seen by one or more secretaries and assistants as well: a handful of people, instead of the scores to hundreds who would normally see copies of a Top Secret document, even one marked “sensitive,” which meant that it was to be especially closely held for bureaucratic or political reasons.

Later, working in the Pentagon as the special assistant to the assistant secretary of defense, I often found myself reading copies of cables and memos marked “Eyes Only” for someone, even though I was not the addressee. And by the time I read this one, as a consultant to the Office of the Secretary of Defense, it was already routine for me to read Top Secret documents. But I had never before seen one marked “For the President’s Eyes Only.” And I never did again.

The deputy assistant to the president for national security, Bob Komer, showed it to me. A cover sheet identified it as the answer to a question that President Kennedy had addressed to the Joint Chiefs of Staff a week earlier. Komer showed their response to me because I had drafted the question, which Komer had sent in the president’s name.

The question to the Joint Chiefs was this: “If your plans for general [nuclear] war are carried out as planned, how many people will be killed in the Soviet Union and China?”

Their answer was in the form of a graph. The vertical axis showed the number of deaths, in millions. The horizontal axis showed the amount of time, in months. The graph was a straight line, starting at time zero on the horizontal, with the vertical axis indicating the number of immediate deaths expected within hours of our attack, and then slanting upward to a maximum at six months—an arbitrary cutoff for the deaths that would accumulate over time from initial injuries and from fallout radiation. The representation below is from memory; it was impossible to forget.

The lowest number, at the left of the graph, was 275 million deaths.

The number on the right-hand side, at six months, was 325 million.

That same morning, I had drafted another question to be sent to the Joint Chiefs over the president’s signature, asking for a total breakdown of global deaths from our own attacks, to include not only the Sino- Soviet bloc but all other countries that would be affected by fallout as well. Komer showed it to me a week later, this time in the form of a table with explanatory footnotes.

In sum, another hundred million deaths, roughly, were predicted in Eastern Europe, from direct attacks on Warsaw Pact bases and air defenses and from fallout. There might be a hundred million more from fallout in Western Europe, depending on which way the wind blew (a matter, largely, of the season). But regardless of the season, another hundred million deaths, at least, were predicted from fallout in the mostly neutral countries adjacent to the Soviet bloc and China, including Finland, Sweden, Austria, Afghanistan, India, and Japan. Finland, for example, would be wiped out by fallout from U.S. ground-burst explosions on the Soviet submarine pens in Leningrad.

The total death toll as calculated by the Joint Chiefs, from a U.S. first strike aimed at the Soviet Union, its Warsaw Pact satellites, and China, would be roughly six hundred million dead. A hundred Holocausts.

I remember what I thought when I first held the single sheet with the graph on it. I thought – this piece of paper should not exist. It should never have existed. Not in America. Not anywhere, ever. It depicted evil beyond any human project ever. There should be nothing on earth, nothing real, that it referred to.

One of the principal expected effects of this plan—partly intended, partly (in allied, neutral, and satellite countries) undesired but foreseeable and accepted “collateral damage”—was summarized on that second piece of paper, which I held a week later in the spring of 1961: the extermination of over half a billion people.

From that day on, I have had one overriding life purpose: to prevent the execution of any such plan.

© Daniel Ellsberg, 2017

Excerpted from prologue of THE DOOMSDAY MACHINE: Confessions of the Nuclear War Planner by Daniel Ellsberg, published by Bloomsbury.