North Korea's Deadly Weapon: What is a Hydrogen Bomb and How Much Damage Could It Do?

First H-bomb test
The mushroom cloud of the first test of a hydrogen bomb, "Ivy Mike," as photographed on Enewetak, an atoll in the Pacific Ocean, in 1952, by a member of the United States Air Force's Lookout Mountain 1352d Photographic Squadron. North Korea claimed it had tested a hydrogen bomb on Sunday. Handout/Reuters

North Korea is not backing down.

Despite sustained international pressure and fiery rhetoric from U.S. President Donald Trump, Kim Jong Un's secretive regime said it had carried out its most powerful nuclear test yet, and the first since Trump came to office. If confirmed, the test would mark a significant escalation in Pyongyang's nuclear program, in particular because of the nature of the weapon that was tested.

North Korean state media claimed the country had tested a hydrogen bomb capable of being loaded onto an intercontinental ballistic missile (ICBM) with "perfect success" on Sunday. Seismologists at the U.S. Geological Survey reported a 6.3 magnitude earthquake, likely as a result of the test. The artificial earthquake was felt over the border in China and sparked an angry response from Beijing.

Read more: What you need to know about North Korea's hydrogen bomb test

While the nature of the test has not yet been independently confirmed, world leaders will be worried by Pyongyang's claims. Hydrogen bombs have never before been used in warfare and are capable of generating destructive power many times that of the atomic bombs dropped by the United States on the Japanese cities of Hiroshima and Nagasaki at the conclusion of World War II.

Kim Jong Un nuclear weapons
North Korean leader Kim Jong-un provides guidance on a nuclear weapons program in this undated photo released by North Korea's Korean Central News Agency in Pyongyang on September 3. KCNA via Reuters

What is a hydrogen bomb?

Hydrogen bombs are two-stage thermonuclear devices. Whereas an atomic bomb generates energy through the process of nuclear fission—splitting the nucleus of an atom—of nuclear materials such as uranium or plutonium, a hydrogen bomb goes one step further. In an H-bomb, the fission process takes place in a chamber of hydrogen gas; the energy released by nuclear fission causes hydrogen atoms to fuse. This process consequently releases neutrons, which feed the fission process in an explosive chain reaction.

What does North Korea say about its H-bomb?

Kim visited nuclear scientists and witnessed the loading of an H-bomb onto an ICBM, North Korea's state news agency KCNA News reported on Sunday, without specifying the date of the visit. The report claimed that the "explosive power" of the hydrogen bomb was "adjustable from ten kilotons to hundreds kiloton [sic.]." The weapon was described as "a multi-functional thermonuclear nuke...which can be detonated even at high altitudes for super-powerful EMP [electromagnetic pulse] attack according to strategic goals."

An EMP attack refers to an huge wave of electromagnetic energy resulting from the detonation of a nuclear weapon. If directed at the electrical grid, a single EMP attack has the potential to knock out power and communications across a massive area, CNN reported.

KCNA News also released pictures of Kim inspecting purported nuclear weapons, but it remains unclear whether the weapons pictured are hydrogen bombs. Experts are also skeptical as to whether North Korea has been able to miniaturize a nuclear weapon so that it could fit on an ICBM and potentially be used to attack the United States.

Has anyone ever used an H-bomb?

Hydrogen bombs have never been used as an offensive weapon, but there have been several confirmed tests. The United States conducted the first H-bomb test in 1952 in the Pacific; the bomb produced a yield of 10,400 kilotons, around 450 times more powerful than the weapon used at Nagasaki. Two years later, the United States conducted its biggest-ever nuclear weapon test: the Castle Bravo test had a yield of 15,000 kilotons.

The Soviet Union holds the title for the largest hydrogen bomb ever tested. To international condemnation, Russia tested the so-called Tsar Bomba in 1961, a 27,000 kilogram bomb that produced a yield of 50,000 kilotons—equivalent to 50 million tons of TNT.

How much damage can an H-bomb do?

The atomic bombs used by the United States in World War II remain the most powerful nuclear weapons ever used in warfare. The so-called "Fat Man," which was dropped on Nagasaki, weighed around 4,700 kilograms and had a yield of of 20 kilotons. The Hiroshima and Nagasaki bombs instantly killed 80,000 and over 70,000 people respectively, while more than 100,000 more people are estimated to have died in the aftermath due to radiation and other factors. Since a hydrogen bomb is capable of generating many times more destructive force than atomic bombs, its use could produce a far higher death toll.

Who else has tested H-bombs?

Besides the United States and Russia, the U.K., France and China have all carried out confirmed tests of hydrogen bombs. Of the other countries that possess nuclear weapons, Israel and Pakistan are not known to have conducted hydrogen bomb tests. India conducted five nuclear weapons tests in 1998 that some reports suggested included a thermonuclear device, but a former coordinator of the program has disputed the claim.​