On January 5, 2016, reports of an unusual seismic event close to a known nuclear test site in North Korea (Punggye-ri) were followed by official North Korean television statements that North Korea had successfully tested a hydrogen bomb. Nuclear weapon tests are no longer a commonplace occurrence, so it’s always a little shocking when it happens. It may even be shocking to the country that conducts it – most recently, North Korea. The famously secretive regime broadcast news of its “safe and perfect” test of an H-bomb to spectators standing in the massive Kim Il Sung Square in the capital Pyongygang shortly after the event. According to the Korean Central News Agency, “There took place a world startling event to be specially recorded in the national history… The DPRK proudly joined the advanced ranks of nuclear weapons states possessing the H-bomb.” The mixture of pride, triumph and aggression that has accompanied announcements following each of North Korea’s tests – in 2006, 2009, 2013 and now in 2016 – always raise the question of what North Korean leaders hope to achieve politically with these tests. The technical aims are obvious. The first test was a dud, so a second test was required. The 2009 test yielded between 2 and 7 kilotons (the Hiroshima blast was 15 kilotons), and the 2013 test a bit better (between 7 and 25 kilotons). The North Koreans stated that the 2013 test “diversified its nuclear deterrence capabilities.” With each test, the North Koreans learn how to improve their devices. Data from the tests help them design more reliable, efficient and ultimately more usable weapons (one hopes that safety and security are also on Kim Jong-un’s to-do list). North Korea is especially aiming for smaller and more powerful warheads so that it can fit a nuclear payload on an intercontinental range missile. Each test helps North Korea advance toward that goal. But was this an H-bomb? And if so, does it really matter? Hydrogen bombs were nicknamed after the heavy isotopes of hydrogen that are used as fuel in the fusion reaction — deuterium and tritium. Unlike fission, an enormous amount of energy is needed to initiate the fusion of atoms. Consequently, weapons designers came up with a two-stage design that uses a smaller fission bomb basically as a spark plug for the fusion fuel. It’s actually the X-rays from the primary that result in the compression of the fusion fuel (radiation implosion) in the secondary. Whereas fission weapons yield explosions in the hundreds of kilotons, thermonuclear warheads can have much higher explosive impact because they are limited only by the amount of fusion fuel. Add stages and you can design a bomb, like the Soviets did, at 100 megatons – almost unimaginably more powerful than the Hiroshima bomb. They don’t have to be large – in fact the US stockpile currently has a warhead (B-83) whose yield can be dialed down into the low kiloton range or maxed out at 1.2 megatons. But to design a thermonuclear warhead in the kiloton range takes a lot of experience, which the North Koreans don’t yet have. It’s no wonder that experts doubt Kim’s claims. But it’s hard to tell. Seismic readings help with an estimation of the yield of nuclear weapon tests, but little else. In this case, a seismic event equivalent to 5.1 on the Richter scale indicates a test of between 10 and 20 kilotons. North Korea might have tested another fission device or a fusion-boosted fission device. The latter does trigger a fusion reaction within heavy hydrogen isotopes (deuterium and tritium) so Kim wouldn’t be entirely wrong to call it a hydrogen bomb, but the point of the design t is to make the fission reaction more efficient. This would be a bad development since it would help North Korea lighten its warheads to extend the range of its ICBMs. That’s why it’s no time for complacency even if the H-bomb of justice is not what it seems. North Korea has been busier than ever testing its ballistic missiles and it won’t be too long before its warhead improvements allow its missiles to reach the continental United States. If Kim Jong-un used the test for political reasons to consolidate his power before the historic Workers Party Congress scheduled for the spring, he may be feeling more secure afterwards and in the mood to talk. If so, the world community should take every opportunity to drive home two points: that engagement is the key to security and that nuclear weapons are not. If not, leaders still must convey to Kim that this most recent test is certainly not a “driver’s license” for nuclear weapons. While Kim may appear giddy at the thought of having the H-bomb, he should be a lot more sober: like driving, caring for and maintaining nuclear weapons quickly becomes a chore requiring eternal vigilance to avoid accidents. And although they are rare, head-on collisions do occur, resulting in certain death for the drivers. Sharon Squassoni is a senior fellow at the Center for Strategic and International Studies (CSIS) in Washington, DC, where she has directed the Proliferation Prevention Program since 2010. She previously held positions at the Congressional Research Service, the US Department of State and the Arms Control and Disarmament Agency. She is a member of the Science and Security Board of the Bulletin of Atomic Scientists