North Korea defies predictions — again — with early grasp of weapons milestone

The device that shook the mountains over the Punggye-ri test site on Sunday represented a quantum leap for North Korea’s nuclear capability, producing an explosion at least five times greater than the country’s previous tests and easily powerful enough to devastate a large city.

And if studies confirm that the bomb was a thermonuclear weapon — as North Korea claims — it would be a triumph of a different scale: a major technical milestone reached well ahead of predictions, putting the world’s most destructive force in the hands of the country’s 33-year-old autocrat.

The feat instantly erased lingering skepticism about Pyongyang’s technical capabilities and brought the prospect of nuclear-tipped North Korean intercontinental ballistic missiles a step closer to reality, U.S. analysts and weapons experts said. Many predicted that a miniaturized version of the presumed thermonuclear bomb would soon be in North Korea’s grasp, and that it probably already exists. 

“North Korea has achieved a capability to wipe out a big chunk of any major city,” said Sue Mi Terry, a former senior analyst on North Korea at the CIA and now managing director for Korea at the Bower Group Asia. “If the North didn’t test a hydrogen bomb, as they said they did this time around, they will get there very soon.” 

The blast, at exactly noon local time in the country’s northeastern mountains, produced seismic waves equivalent to a 6.3-magnitude earthquake, or 10 times as strong as the country’s last nuclear test, which occurred a year ago this week. A conclusive analysis will take days or weeks, but weapons experts said the sheer force of the explosion is highly suggestive of a thermonuclear bomb. Sometimes called hydrogen bombs or H-bombs, these second-generation nuclear devices entered U.S. and Soviet arsenals in the 1950s, threatening adversaries with a vastly greater destructive force compared with atomic bombs dropped on Japan in the final days of World War II.

Because of the H-bomb’s relatively complex two-stage design, many experts thought it would be months, or perhaps years, before North Korea’s scientists could master the necessary technology. When Pyongyang boasted last year that it had tested a thermonuclear device, many U.S. experts dismissed the claim as propaganda.

By early Sunday, Washington time, the skepticism had mostly evaporated.

“There’s little doubt in my mind,” said James M. Acton, a physicist and co-director of the Nuclear Policy Program at the Carnegie Endowment for International Peace, a Washington think tank. “North Korea has been hinting for a while that it was working on an H-bomb — even apart from the photos it released last night — so this should not come as a huge surprise. But it does represent a significant technological advance.”

The apparently successful test came hours after leader Kim Jong Un appeared on state-run television with what appeared to be a prototype of a new North Korean thermonuclear bomb, in a remarkable display of his confidence in the capabilities of his country’s weapons engineers. Given other recent technical gains in producing long-range missiles and miniaturized warheads, U.S. experts said there is little doubt about North Korea’s ability to eventually master all the steps needed to send a nuclear-tipped missile halfway around the world.

Although it is not known for certain that North Korea can build a miniaturized thermonuclear warhead that can fit on a missile, Acton said, “I believe we have to assume it can.”

Peter Zimmerman, a nuclear physicist and former chief scientist for the Senate Foreign Relations Committee, said initial calculations based on seismic readings suggested a device with a yield of up to 200 kilotons — a destructive force 13 times as powerful as the bomb dropped on Hiroshima, Japan, in 1945, and probably “too big for a pure fission bomb.” Moreover, the prototype displayed by Kim on the eve of the test “pretty well shows they know the essentials of a thermonuclear device design,” he said.

Several other nuclear experts noted that the vaguely peanut-shaped metallic device shown on North Korean television bore features that were broadly consistent with a two-stage hydrogen bomb, although it did not resemble any weapon in past or current U.S. arsenals.

“This was a major step forward for the [North Korean] scientists and engineers,” Zimmerman said. “Their first test was a dud; the next couple were very low yield. Since then, their yields have steadily gone up. But this is a discontinuity indicating the introduction of new technology.”