Such stories of near-mistakes illustrate why “nuclear surety” has become paramount. According to former nuclear-weapons officers I talked with, from the previous commander of U.S. Strategic Command (Stratcom) down to a retired U.S. Air Force Minuteman III launch officer, it was the single most important thing they thought about, trained for, and responded to, day in and day out, every minute that they were on patrol, in the silo, or making national-level decisions about America’s nuclear force. Nuclear surety, in other words, is the business of nuclear weapons.

“We have a culture of asking ‘What aren’t we doing right?’ to try and avoid mistakes,” said retired U.S. Navy Admiral Cecil Haney, who was the commander of U.S. Strategic Command from 2013 to 2016, during which time he was the senior nuclear war-fighting officer in the U.S. military. But, he asked, “Will North Korea take shortcuts in a very expensive enterprise?”

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The risks of a nuclear program start with the very act of building a bomb. Americans just don’t know how lax the standards may be in the laboratories and assembly plants where North Korea’s bombs are ostensibly made, nor how many safety mechanisms will be built into their warheads. The danger of lax standards is compounded by normal wear and tear on nuclear systems. The more use one makes of these systems—by flying bombers, sailing submarines, or moving missiles—the more likely accidents are to occur. During the Cold War, the relentless pace of constant nuclear alerts led to numerous mishaps. In Operation Chrome Dome, for example, U.S. B-52s carrying thermonuclear bombs were kept constantly in the air, flying to predetermined points around the Soviet Union, for eight full years. Between 1960 and 1968, five major accidents occurred, ultimately leading to the cancelation of the program.

Nuclear-weapons accidents such as these, called “broken arrows,” nearly turned into catastrophe more than once. In 1961, a B-52 participating in Operation Chrome Dome flying out of Goldsboro, North Carolina, developed a leak during its airborne refueling. Before the bomber could make it back to base, the crew was forced to eject, and the plane broke apart in midair, releasing two live nuclear bombs. When one of the bombs hit the ground, a firing signal was sent. The four-megaton weapon did not detonate only because its fourth and last safety switch held in place, the other three 50-cent pieces of equipment having armed themselves.

North Korea almost certainly won’t have nuclear bombers, but the bulk of its ground-based force will likely be dispersed onto mobile launchers, which can pose its own set of problems. Though some of the North’s missiles are apparently solid-fueled, most are liquid-fueled. Even the more stable liquid propellants used today are among the most toxic substances on earth, and transfer accidents have been a hazard of the job. These mobile launchers are fitted onto large trucks that roam the countryside, making them difficult for enemies to target and destroy, but the very nature of such a decentralized force also means a localized response to any problems. Only on-site North Korean nuclear launch teams would be available to correct an electrical glitch that starts a firing sequence for a loaded missile, or repair a faulty missile or one that has been damaged in some other way while being transported, in order to prevent a potential explosion or unauthorized launch. Such expertise may not be available or reach the problem in time.