In 1964, I attended a talk by a Strategic Air Command major general who described how, during the 1962 Cuban crisis, he carried out an order to lead US bombers on what he believed at the time was a nuclear attack on the Soviet Union. I chatted with him before his talk and came away impressed not only with his intelligence, but also with his kindness and thoughtfulness; he was very proud of a son that worked in a mental hospital. He began his talk by telling us how difficult it had been to say goodbye to his wife before departing. He then went into detail on the extensive planning and long and rigorous training that goes into such a mission and the tremendous discipline it requires. He talked about the difficult takeoff and how it felt to respond to such an order; if he got a coded “GO” signal before the bombers reached a certain point in the Arctic, he was to lead them to their targets. He said his crews understood that dropping the several megatons of nuclear explosives each plane carried would have awful consequences, and that they might not survive.

We in the audience knew, as there had been no nuclear war, that he must have turned around at some point. What a relief that must have been, I thought, to give the order to head for home. But, no, I was wrong. The general drew himself up, paused, looked out across the audience, and told us that giving the order to abandon his nuclear mission was the most disappointing moment of his entire life. It rocked me back. Did I get him wrong? After some reflection I decided that I wouldn’t let this revelation change my opinion of him as a good and intelligent man.

But I would have to rethink my view of human nature, and its ability to avert disaster.

I abandoned my notion that the people in the nuclear weapon complex—from scientists to military users—really hoped the stuff would never be used. Maybe that is what they themselves believed—SAC’s motto was “Peace is our profession”—but not many persons, no matter how well intentioned, can spend a lifetime working on something, or training for something, no matter how awful, without at some level wanting to see it work. The moral restraints that, I had imagined, would prevent Armageddon were flimsier than I had thought.

Scientists are also not immune from wanting to see their handiwork in action. When the news of the 1945 Hiroshima blast was announced at Los Alamos, where the bomb was made, many of the lab personnel cheered. They weren’t of course cheering 100,000 deaths; they were cheering the successful test of their device.

Again in the 1960s, I attended a presentation on “peaceful nuclear explosions” by the director of the Livermore nuclear weapons laboratory. At that time, so-called peaceful nuclear explosives were still in vogue, strongly supported by the Atomic Energy Commission as a highly useful civilian spin-off from nuclear weapon development. The laboratory director told us confidentially that the real reason for conducting civilian bomb tests was different: The civilian tests were essential for making the public comfortable with nuclear explosives. Only then could the military count on getting a presidential release for their use in wartime.

Today, Los Alamos, the original nuclear weapon laboratory, sublimates the weapon scientists’ need to feel their work is used by assuring them that—I quote from the lab’s web page—“Nuclear weapons are used every day … as a disincentive to adversaries from taking hostile and aggressive actions against the US and its allies.” Thinking in terms of threatening the world every day not to do things we don’t like may make weapon designers feel more useful. But considering that we are not the only ones on the planet with these weapons, it is a problematic stance for the country.

It seems to have dropped from the world’s consciousness that in nine countries around the world, highly trained and dedicated military officers sit ready to launch nuclear-tipped missiles. Upon receipt of a valid order from their superiors—possibly not even from the country’s leaders—they will turn keys and close firing circuits; hundreds of thousands, perhaps millions, will die, and the world will become a different, and probably much more brutish, place. The nuclear war gurus conclude this only increases the importance of maintaining nuclear deterrence.

But deterrence is in the mind, a matter of psychology. Sometimes minds do strange things.

Consider the India-Pakistan nuclear standoff. Both have sizeable nuclear warheads on long-range rockets; in principle they balance each other out. But India, stung by terrorists it said had come from Pakistan to attack Mumbai in 2008, announced it would in the future respond with a punishing military attack, but one so limited as to avoid triggering a nuclear response from Pakistan. To counter this Indian strategy, Pakistan has developed small-yield, short-range nuclear weapons, which it says it would use against India’s limited conventional attacks. Thus, it says, it has blocked all Indian conventional options. But has it? Will Pakistan now refrain from supporting anti-Indian terrorists, if that is what it has in fact been doing? And will India put aside its response strategy? The danger is of course that miscalculations leading to the use of small nuclear weapons by Pakistan could trigger India to use its strategic nuclear weapons—and all-out nuclear war.

When asked about this, an unworried Pakistani general asked why would anyone in India launch an attack, especially when a devastating response is likely? The answer is that national leaders, being human, often do foolish things, sometimes out of miscalculation, sometimes because they feel trapped, sometimes out of frustration. Sometimes there are communications problems.

Consider again the Cuban Missile Crisis. It was long ago and the technical systems have changed; but human nature hasn’t changed. It came about because Soviet Chairman Nikita Khrushchev tried a dangerous short cut to nuclear parity with the United States. Robert McNamara, who was US defense secretary during the crisis, lost no opportunity in later years to point out that the confrontation was even more dangerous than it seemed at the time. Unbeknownst to the United States, the Soviets had battlefield nuclear warheads in Cuba. It turns out, however, that McNamara, as he was surprised to learn 30 years later, was also unaware at the time of the extent of the forward lean of our nuclear forces.

I happen to have been with McNamara when a former Air Force colonel who had been in the underground command center at SAC’s Nebraska headquarters during the crisis described what happened there on the most critical day. McNamara was shaken; he evidently did not know the full extent of steps the SAC commander, General Tommy Powers, had taken on his own authority. The Air Force general in charge of the SAC underground command center in Nebraska gave the order to close the center from the outside world, apparently the only time this has ever happened. He told the targeting staff that the moment they had trained for all their lives had arrived. He expected a missile launch order momentarily and also expected they would all likely die from a Soviet response. Each individual was permitted a call to his family to say goodbye, but was not permitted to say why he was calling. The conversations were about scraped kids’ knees and sick dogs. It was a scene straight out of Dr. Strangelove. McNamara was open-mouthed; he mumbled to the colonel: “We have to talk.”

I expect that communications about use of US nuclear weapons work much better today. But one thing has not changed: the cult of toughness in high-level decision-making. On another occasion, well after he was defense secretary, McNamara told me he would not have approved nuclear weapon use against a conventional Soviet attack in Europe, even though to do so was declared US policy. I asked whether he ever told this to President John Kennedy or National Security Advisor McGeorge Bundy. He said he hadn’t because they would have considered him weak. The defense secretary who had intimidated so many with his toughness was himself intimidated by the potential charge of weakness. In high power circles it is politically fatal to be thought “soft.”

This problem has been with mankind since the beginning of civilization. Thucydides writes about it in his history of the war between Athens and Sparta. Once war fever is running, prudence is easily confused with cowardice. At the start of Athens’s disastrous Sicilian campaign, “the few that liked it not, feared to appear unpatriotic by holding up their hands against it, and so kept quiet.”

The flexing of nuclear muscles on the assumption that “deterrence” will keep the weapons from ever being used reminds me of tabletop experiments that were carried out at Los Alamos during World War II to determine the “critical mass” of nuclear explosives. Physicists nudged two sub-critical masses closer to each other by tapping them lightly with a screwdriver and measuring the increased neutron count. Richard Feynman called this “tickling the dragon’s tail.” They could get away with it so long as the two sub-critical masses stayed sufficiently apart. One day the experimenter slipped, pushed the two pieces too close together, and received a lethal dose of radiation.

In a similar way, if we slip, and nuclear weapons are used, the consequences will be awful. It’s not just that there will be considerable devastation; the reality of nuclear war will force radical changes in the way we organize our lives. The basic elements of our civilization—our cities, our economic systems, our civil liberties—are based on the belief that these weapons will not be used. But in the end, the restraints on their use are psychological, just plate glass. If that shatters, the organizing principles of the world will change dramatically. This is no idle concern, for there is a self-destructive defect in us. It has to be quarantined if we are to survive.