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North Korea’s scarily plausible claim to have a miniaturized nuclear warhead, explained

Zack Beauchamp is a senior correspondent at Vox, where he covers ideology and challenges to democracy, both at home and abroad. Before coming to Vox in 2014, he edited TP Ideas, a section of Think Progress devoted to the ideas shaping our political world.

North Korea's regime is well-known for making outrageous and often false claims. But its latest claim, made on Wednesday night, seems, while far from proven, at least plausible: that it had successfully miniaturized a nuclear weapon such that it could fit on top a warhead.

North Korea's state media released some photos, including the one above, as proof. Nuclear experts say the metal sphere does indeed resemble a warhead, and that North Korea's history of nuclear tests suggests it is at least within the realm of possibility that the country could have achieved miniaturization.

If North Korea's claim is true, it would mean the country could theoretically put a nuclear warhead onto one of its missiles, which it has been developing in parallel, thus giving its nuclear program far more military potential.

What's a miniature nuclear device? And does North Korea have one?

No matter the size, this is still the basic idea.
Romolo Tavani/Shutterstock

There are two primary ways modern militaries deliver strategic nuclear weapons. One, they can drop a bomb from a plane, as in Hiroshima or Nagasaki. Two, they could fire a long-range missile from a submarine or a ground-based silo. In order to make the latter work, you need a much smaller nuclear device than you do for the former — otherwise it won't fit into a warhead.

This is why miniaturization is so important to North Korea. Without that capability, the long-range missiles it's been testing for years are just really expensive conventional weapons.

So has North Korea done it? The photographs it released show three parts related to a warhead: a heat shield, a core sphere containing the fissile material, and a fuel-filled cylinder. Nuclear experts think it's plausible that these parts aren't just for show — that they could be real.

"Of course they have," Jeffrey Lewis, director of the East Asia Nonproliferation Program at the Middlebury Institute of International Studies at Monterey, tweeted. "Ten years and four nuclear tests later you're still at 'maybe?'"

Lewis cited a piece he wrote last year for the Korea analysis site 38North. North Korea, he'd written, has been testing conventional explosives for years. Miniaturization is partly a matter of improving the conventional explosives used to trigger the nuclear device. So this research appeared to be aimed at developing miniaturization technology, and Lewis also sees hints from North Korea's nuclear tests that it was trying to build a miniaturized device all along — suggesting the successful nuclear tests could have been bringing them much closer.

In 2013, North Korea claimed to have "miniaturized" a nuclear device. It tested a nuclear bomb that year — seismographs in the region picked it up — and again in 2016, claiming both had been miniaturized.

"It seems very plausible to me," Lewis wrote last year, that North Korea had developed a warhead. "Lots of states have moved quickly to develop relatively smaller devices."

Still, it's impossible to say for sure whether North Korea was telling the truth. And there's long been debate over the country's technological capability.

North Korea "has had tremendous trouble overcoming various technical hurdles that US experts assumed would not pose any serious difficulties at all," Jacques Hymans, a professor at the University of Southern California, said in a 2013 interview with the Federation of American Scientists. "Even its recent tests can be said to have been 'successful' only relative to the ridiculously low bar that Pyongyang had set with its prior disastrous test failures."

As for the device in this week's photo, it "looks pretty serious," Melissa Hanham, a senior research associate at the James Martin Center for Nonproliferation Studies, told the Diplomat on Tuesday. But, she continued, "It's very hard for us to determine or for them to demonstrate the capability short of testing it on the tip of a flying missile."

One key outstanding question, for example, is whether the warhead has a working "reentry vehicle," or RV. Intercontinental ballistic missiles work by exiting Earth's atmosphere; for a missile to work, it needs to be able to survive the heat created by reentry. Otherwise, it will either be thrown way off target or burn up entirely.

And that's a question of missile design, not of miniaturization. North Korea needs to accomplish both in order to test, and thus prove, that it has miniaturized a device.

The photos North Korea released appear to show something resembling a possible reentry vehicle:

As for whether the apparent reentry vehicle works, or is even real, that's "the $64,000 question," Joshua Pollak, an associate fellow at the Royal United Services Institute, tweeted after looking at the photos.

Why a miniaturized North Korean bomb would and wouldn't matter

Kim Jong Un Haircut KCNA

If North Korea is telling the truth, then its nuclear arsenal would now be much more dangerous. Because missiles are harder to shoot down than planes, they could pose a more viable threat to neighboring countries such as Japan. And if North Korea succeeds in developing missiles that could reach all the way to the American mainland (as it claims), that would threaten the US as well.

This is worrying. North Korea is an unpredictable dictatorship with opaque internal politics, constantly in tension with South Korea, Japan, and the United States. Its nuclear arsenal is improving (albeit slowly) as time goes on. That isn't an ideal situation!

But don't worry — this doesn't mean North Korea is going to nuke Hawaii or Tokyo out of nowhere. The regime is erratic and eccentric but ultimately focused on self-preservation, and the logic of deterrence still holds. There's no reason to believe the country would start a nuclear war, which it would absolutely lose.

Rather, North Korea's nuclear program is likely designed for a combination of deterrence and coercion. The former means preventing its much stronger enemies, including the United States, from attacking, by threatening that any attack would bring nuclear retaliation. This would allow North Korea to get away with even more bad behavior than it does already.

As for the latter — coercion — it's tough to predict exactly what would happen. North Korea has already demonstrated it is willing to threaten military force to get concessions from its enemies, but it's hardly believable that Kim Jong Un would start a nuclear war to try to convince the UN to send more food aid.

So long as North Korea's enemies — particularly South Korea and the United States — are capable of destroying the North, the regime is very unlikely to actually use its nuclear weapons. No matter how advanced they get.