North Korea’s latest nuclear weapon test is by far its largest yet. Preliminary analysis of the seismic signals it generated while exploding under a mountain last week suggest it was at least 100 kilotons in strength, and the North Koreans themselves claim it was “hundreds” of kilotons. (The bomb that destroyed Hiroshima was 15 kilotons.) This has led many analysts to suggest that North Korea has in fact developed a working hydrogen bomb.
North Korea has backed up its claim—sort of—by releasing photographs showing a peanut-shaped weapon that could fit into a missile nose cone. While an external weapon casing cannot tell one much about what actually is inside the weapon (it might be filled with jelly beans for all we know), it’s the clearest signal yet that the North Koreans desperately want the world to consider them a thermonuclear power.
That North Korea should have to go through such theatrics is an interesting inversion of more typical behavior of nuclear states. In the case of the United States, nuclear weapons are shrouded in secrecy, and the casings themselves kept largely invisible until they have been phased out of service. The shapes of the first nuclear weapons, Little Boy (Hiroshima) and Fat Man (Nagasaki), were considered national secrets until 1960, a full 15 years after their first use in war. The exact appearances of the warheads that top U.S. ballistic missiles are still secret (the “dunce cap” reentry vehicles that they fit inside are not); of the warheads that makeup the American “enduring stockpile,” there are a few whose images have been declassified—they look like thermos bottles—but they are all weapons that are used in gravity bombs dropped out of planes or cruise missiles.
What’s in a warhead shape? Quite a lot, actually: In many cases, a trained eye can get a lot of “useful” design information out of them, especially if combined with reasonable assumptions about how much plutonium might be in the weapon, how much the weapon weighs, and how explosive the weapon is. The United States doesn’t like to show pictures of its warheads, lest they help other states reverse engineer its most sophisticated weapons.