A look at North Korea's 6 nuclear tests

North Korea announced Sunday that it conducted its sixth nuclear test. Here's a look at each of its attempts to join the nuclear weapons club:

Oct. 9, 2006

After years of saying it could do so, North Korea became the ninth country to test a nuclear weapon. Like all its tests, it took place in underground tunnels in a remote, mountainous region. Experts estimated the plutonium explosion measured less than 1 kiloton, or approximately one-tenth the size of the atomic bomb the U.S. dropped on Hiroshima in 1945. Although the test was described by international monitors as a "fizzle," it prompted the United Nations Security Council to impose economic sanctions on North Korea.

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May 25, 2009

Its second nuclear test took place when President Obama was in office for just four months. The test was immediately hailed by North Korea's state news agency as a "new higher level in terms of its explosive power and technology of its control." Its estimated explosive yield was 2 to 8 kilotons. A month earlier, the communist nation launched a satellite into space that many viewed as an attempt to demonstrate it would soon be capable of striking the U.S. with a long-range missile. The U.N. Security Council responded by imposing fresh sanctions that banned all weapons exports from North Korea and all imports apart from small arms.

Feb. 13, 2013

For the first time, North Korea alleged that it conducted a successful nuclear test using a uranium-enriched device. Although never confirmed, it marked a potentially dangerous new development for its nuclear ambitions because it meant scientists may have learned how to miniaturize bombs that could be placed atop long-range missiles. The use of uranium would also allow North Korea to stockpile bombs, not possible with plutonium because of its limited supply. The Security Council, which had banned satellite launches in December 2012, added a fourth resolution that expanded rights to inspect cargo ships and further restricted North Korea's financial transactions.

Jan. 6, 2016

North Korea announced it had successfully tested its first hydrogen bomb, a much more powerful device. But the U.S. and other governments have doubted that claim. Experts aren't sure whether the device was miniaturized. The ability to detonate a hydrogen bomb is a great concern because they unleash massive amounts of energy by using nuclear fusion. An H-bomb uses an atomic (fission) bomb as a trigger. Sanctions were expanded to include individual diplomats, companies and institutions. The U.N. Security Council also banned countries from supplying aviation fuel and other bomb-producing natural resources to North Korea. The sanctions were bolstered by support from China, North Korea's economic lifeline.

Sept. 9, 2016

North Korea's fifth test reflected its determination to be a nuclear-armed country despite ever tougher sanctions. North Korea said the latest test is of a nuclear warhead designed to be mounted on ballistic missiles. That claim was not immediately verified as accurate. It drew a strong rebuke from ally China, which said it would protest the test with North Korea's ambassador in Beijing. The U.S. called the test “yet another flagrant violation” of sanctions resolutions as well as a “serious provocation.”

Sept. 3, 2017 

North Korea’s state-run broadcaster said the country had successfully conducted a test of a hydrogen bomb that can be loaded onto its new intercontinental ballistic missiles. The claim that it was a hydrogen bomb and that it could be loaded on a missile could not immediately be confirmed in the West, but South Korea estimated the test to have a strength of 100 kilotons. That yield would be five-to-10 times more powerful than the 2016 test. President Trump tweeted that "North Korea is a rogue nation which has become a great threat and embarrassment to China, which is trying to help but with little success."

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