North Korea’s sixth nuclear test on September 3 sent shockwaves across the globe when tremors of 6.3 magnitude, believed to have been triggered by the detonation of a hydrogen bomb, sent seismographs at numerous seismic stations worldwide into operation.

North Korean leader Kim Jong-un made it clear in a speech as early as October 2015 – when the world was still skeptical of the regimes’s ability to make atomic bombs – that his country had developed thermonuclear weapons.

Now we know that Kim was not just swaggering his bravado.

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A still from Korean Central Television shows Kim signing an order to launch the H-bomb test.

On that September morning Pyongyang mouthpiece Rodong Sinmun (Workers’ Newspaper) ran a front-page feature about Kim’s visit to a nuclear research institute and disseminated photos of him inspecting a dumbbell-shaped hydrogen-bomb model, about 1.2 meters long and 90 centimeters in diameter, hours before the latest nuclear test was conducted, to the world’s consternation.

The newspaper pronounced that afternoon the successful test of a miniaturized hydrogen warhead fit for North Korea’s Hwasong-14 intercontinental ballistic missile, which was first fired on July 4 – Independence Day in the United States – and pierced through Japan’s airspace for almost 1,000 kilometers.

Korean Central News Agency has also stressed that the test didn’t cause any nuclear leaks or contamination of the areas in the vicinity.

A Korean Central Television news program announces the successful test of a hydrogen bomb.

Initially there were doubts about whether it was a genuine hydrogen bomb, as no photo of a typical mushroom of smoke and flames was dispatched, but before long the powerful man-made quake and aftershocks corroborated the substance and magnitude of Pyongyang’s claim.

The blast yield of the bomb, believed to have been tested in the northeastern Punggye-ri Nuclear Test Site less than 100km from the border with China’s Jilin province, may be three to 7.8 times that of the Fat Man device used in the bombing of Nagasaki in 1945, according to estimates by Chinese military experts. The Nagasaki bomb’s yield was of 21 kilotons; South Korea said the yield of the North’s bomb was 16kt.

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A satellite mage of the Punggye-ri Nuclear Test Site. Photo: Reuters

A senior engineer with the People’s Liberation Army Air Force told Beijing-based military magazine Naval & Merchant Ships that Pyongyang had highlighted its breakthrough in adjusting the blast yield of its hydrogen bombs from 10,000 tons to 100,000 tons, as well as a series of hard technical nuts it had cracked, such as producing enough deuterium and the extremely rare tritium, necessary agents for thermonuclear fusion.

Pyongyang may have acquired the technology for the mass production of lithium deuteride, a compound that can release tritium when exposed to neutrons.

A September 2015 report by Seoul’s National Intelligence Service also confirmed Pyongyang’s progress in producing the vital fuel material to trigger fusion.

It will take time to confirm whether it was a weaponized H-bomb or merely an experimental test of a prototype, as experts say Seoul and Tokyo are yet to collect and analyze nuclear residue that may have spread into the air.

Meanwhile, North Korean Foreign Minister Ri Yong-ho has been sending out word that the next hydrogen-bomb test might be done somewhere in the Pacific Ocean.