The H-bomb: What is it? Who has it? Why it matters

By Ed Payne and Tim Hume, CNN
Story highlights
North Korea claims to have tested a hydrogen bomb
Hydrogen bombs can be thousands of times more powerful than the only atomic bombs ever used
(CNN)— North Korea announced Wednesday that it had successfully tested a hydrogen bomb.
If true, it now processes something much more powerful than the weapons it has tested in the past.
The nuclear age is 70 years old, and while relatively few nations possess the power, the potential consequences of North Korea upping its nuclear game from a basic atomic bomb to a hydrogen bomb has caught the world's attention.
Here's why.
Nuclear weapons: Who has what?
A quick lesson in fission versus fusion
If Pyongyang has mastered the technology, it has made a major step forward in its nuclear capabilities .
The plutonium-based atomic weapons it tested up until this point were powerful enough -- the United States dropped such weapons on Japan to end World War II -- but a hydrogen bomb made with uranium ups the ante many fold.
Atomic bombs use a process called fission. They split plutonium into smaller atoms, releasing massive amounts of energy
The A-bombs dropped by American forces on Hiroshima and Nagasaki in 1945 killed more than 200,000 people
Hydrogen bombs use fusion. Instead of splitting bigger atoms, they combine smaller atoms like hydrogen to release a much bigger nuclear punch -- thousands of times more powerful than the only nuclear weapons that have been used in warfare.
"What thermonuclear weapons do is increase the potential yield by enormous amounts. The amounts that can be released by thermonuclear weapons are phenomenal," said Martin Navias, senior fellow at the Centre for Defence Studies at King's College, London.
The most powerful nuclear weapon ever detonated was the Tzar Bomba, a hydrogen bomb tested by the Soviet Union in 1961, he said. It yielded a blast of 50,000 kilotons, or 50 megatons, dwarfing the force of the Hiroshima and Nagasaki bombs.
With the development of an H-bomb, reclusive North Korea would be that much more of a threat.
A quick lesson in how it works
A hydrogen bomb is a complex bit of machinery. It's basically two bombs in one.
While it gets its bang from fusion, it takes a lot of heat to get the process started -- to get the atoms to smash together and start a nuclear chain reaction. That's why they're called thermonuclear weapons.
What better way to do that with than another much smaller nuclear weapon. An atomic bomb works as the trigger to set off the hydrogen bomb. The two explosions are almost simultaneous.
The nuclear arsenals of the United States, Russia, United Kingdom, France and China are made up of these types of weapons.
India and Pakistan are believed to have atomic bombs.
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North Korea ' s nuclear ambitions
North Korea has described itself as a " nuclear weapons state both in name and reality " and experts warn that by 2020 it could have anywhere from 20 to 100 weapons capable of hitting its neighbors or even the United States. How did we get here ?
December 12 , 1985
North Korea joins the Nuclear Non-Proliferation Treaty (NPT)
Pyongyang ratifies the United Nations Treaty on the Non -Proliferation of Nuclear Weapons, but does not bring itself into compliance . North Korea would fully withdraw from the Treaty in 2003 .
1993
Early warnings over North Korea ' s nuclear weapons program
The International Atomic Energy Agency ( IAEA) accuses North Korea of violating the NPT , leading Pyongyang to threaten withdrawl but ultimately to agree to allow inspectors .
October 21 , 1994
U. S . and North Korea sign agreement
North Korea pledges to freeze and eventually dismantle its nuclear weapons program in exchange for international aid to build two nuclear power stations.
November 17 , 1998
Pyongyang talks
The U. S. and North Korea hold high - level talks in Pyongyang, with the Americans demanding to inspect an underground facility believed to be being used to develop nuclear weapons .
February 27 , 1999 — March 16 , 1999
Inspections take place
During a fourth round of talks , North Korea allows U. S. access to the site in exchange for U. S. aid in increasing North Korean potato yields . U. S. inspectors find no evidence of any nuclear activity during a visit to the site in May .
September 13 , 1999 — September 17 , 1999
Testing stops , sanctions lifted
North Korea agrees to freeze testing of long - range missiles while negotiations with the U. S. continue . President Bill Clinton agrees to ease economic sanctions against North Korea.
June, 2001
Pyongyang threatens to resume missile tests
North Korea warns it will drop its moratorium against testing missiles if the U. S. does not pursue normalized relations with North Korea.
January 29 , 2002
Axis of Evil
President George W. Bush labels North Korea , Iran and Iraq an " axis of evil " in his State of the Union address. " By seeking weapons of mass destruction , these regimes pose a grave and growing danger, " he says .
October 16 , 2002
Secret nuclear weapons program
The Bush Administration first reveals that North Korea has admitted operating a secret nuclear weapons program in violation of the 1994 agreement. It is unclear whether Pyongyang has any completed nuclear weapons .
December 22 , 2002 — December 31 , 2002
Inspectors expelled
North Korea removes IAEA monitoring equipment from its nuclear facilities and expels inspectors.
January 10 , 2003 — February 26 , 2003
Withdrawal from the NPT
North Korea officially withdraws from the Nuclear Non -proliferation Treaty and reactivates its nuclear facilities.
April 23 , 2003 — April 27 , 2003
North Korea says it has a nuclear weapon
Pyongyang declares it has nuclear weapons , prompting crisis talks between the U. S. , North Korea , South Korea, China, Japan and Russia.
February 24 , 2004 — February 28 , 2004
First series of six-party talks
The U. S. , North Korea, South Korea, China, Japan and Russia meet in Beijing , China for more talks . The summit closes with no major progress but with an agreement for more talks .
February 28 , 2004 — August 2004
Talks continue
The six nations meet for more talks , with North Korea eventually agreeing to freeze its nuclear program in exchange for aid , easing of sanctions and being removed from the U. S. ' list of state sponsors of terrorism . The U. S. wants North Korea to disclose all nuclear activities and allow inspections.
February 10 , 2005
North Korea drops out of talks
Pyongyang drops out of six - party nuclear talks and says it will bolster its nuclear weapons arsenal . North Korea insists on a bilateral non - aggression pact with the U. S. before it will consider dismantling its nuclear program . The U. S. insists Pyongyang must first agree to permanently and verifiably dismantle its nuclear weapons program before it will grant any incentives, including economic assistance and diplomatic recognition.
September 13 , 2005 — September 19 , 2005
Talks resume
North Korea returns to the negotiating table , eventually agreeing to give up its entire nuclear program . Pyongyang releases a statement committing itself to " abandoning all nuclear weapons and existing nuclear programs. "
September 20 , 2005
Never mind
North Korean officials say that their country would begin dismantling its nuclear program only if the U. S. provides a light -water reactor for civilian power . " Without this physical guarantee of the ( light -water reactor ) , our position is not to even dream of us giving up our nuclear deterrence . "
July 4 , 2006
Taepodong - 2 missile test
North Korea test- launches a Taepodong-2 missile along with two short - range rockets, but the long- range missile apparently fails.
July 15 , 2006
U. N. Security Council resolution passed
The U. N . Security Council unanimously passes a resolution demanding that North Korea suspend its missile program . The North Korean ambassador immediately rejects the resolution .
October 9 , 2006
FIRST NUCLEAR TEST
North Korea says that it has successfully tested a nuclear weapon at an underground facility in Hwaderi near Kilju city. South Korea reports detecting an artificial earthquake in the region of the test and later analysis of air samples reveal radioactive debris , confirming Pyongyang 's claims .
February 13 , 2007
Back to the negotiating table
North Korea agrees to close its main nuclear reactor in exchange for an aid package worth $ 400 million .
June 25, 2007 — September 2 , 2007
North Korea " reaffirms " commitment to nuclear disarmament
U. S. envoy to North Korea Chris Hill says that North Korea has reaffirmed its commitment to the nuclear disarmament agreement reached in February and will allow IAEA inspectors back into the country . He later announces that Pyongyang has agreed to fully declare and disable its nuclear programs by the end of 2007 .
September 30 , 2007
Six - party talks resume
At six - party talks in Beijing , North Korea signs an agreement stating it will begin disabling its nuclear weapons facilities . North Korea also agrees to include a U. S. team of technical experts in the disabling activities.
October 2 , 2007 — October 4 , 2007
North and South Korean leaders meet
South Korean President Roh Moo- hyun becomes the first South Korean leader to walk across the Demilitarized Zone separating North and South Korea on his way to a three- day summit with North Korean leader Kim Jong Il . Kim signs an agreement committing to demilitarization and replacing the current armistice agreement with a permanent peace treaty .
December 31 , 2007
Deadline? What deadline ?
North Korea misses a deadline to declare all its nuclear programs , later claiming that it had already provided enough information to satisfy the requirements agreed upon in the six - party talks , a point disputed by other signatories.
May 8 , 2008 — June 27 , 2008
Progress
North Korea hands over thousands of documents pertaining to its nuclear activities, especially related to its production of plutonium , to visiting U. S. official Sohn Kim . In a symbolic gesture, a water cooling tower at the Yongbyon nuclear facility is also destroyed.
December 8 , 2008 — December 11 , 2008
More talks
Another round of six - party talks is held in Beijing , China. The talks break down over North Korea 's refusal to allow international inspectors unfettered access to suspected nuclear sites.
January 2009
Most of North Korea 's plutonium stockpile 'weaponized '
U. S. scholar Selig Harrison meets with senior officials in North Korea. After the meeting he reports that the officials have claimed that North Korea has weaponized most of its plutonium stockpile . The amount of weaponized plutonium is allegedly enough for four to five nuclear bombs .
May 25, 2009
SECOND NUCLEAR TEST
North Korea announces it has conducted its second nuclear test shortly after the U. S. Geological Survey reports a magnitude 4 . 7 seismic disturbance at the site of North Korea 's first nuclear test. The White House reports that North Korea also test- fired a short range missile .
June 12 , 2009
Sanctions and condemnations
The UN Security Council approves Resolution 1874 , condemning North Korea 's May 25 th nuclear test. The UN also imposes new sanctions , banning the sale of most arms to or from North Korea .
November 20 , 2010
New facility
According to a report by Stanford University professor Siegfried Hecker, North Korea has a new nuclear enrichment facility composed of 2 , 000 centrifuges . Hecker was given unprecedented access to North Korea' s facility and documents.
December 17 , 2011
KIM JONG IL DIES
Kim Jong Il dies aged 69 ( or 70 ) , reportedly of a heart attack . According to the KCNA state news agency, during his death a fierce snowstorm paused and the sky glowed red above Mount Paktu . His son , Kim Jong Un , succeeds him as leader .
February 29 , 2012
Missile moratorium
The U. S. State Department announces that North Korea has agreed to a moratorium on long -range missile launches and nuclear activity at Yongbyon , the nation' s major nuclear facility.
April 13 , 2012
Long - range rocket test fails
North Korea 's long- range rocket launch is a failure . Shortly after launch, it breaks apart and falls into the sea . Japan , South Korea and the U. S. believe the purported space program to be a cover- up for testing a long- range ballistic missile .
December 12 , 2012
Satellite launch
North Korea successfully launches an Unha -3 long- range rocket from the Sohae Space Center in Cholsan County and puts a " working satellite " into orbit , days after Pyongyang suggested the launch could be delayed.
January 24 , 2013
Sworn enemies
North Korea 's National Defense Commission says it will continue nuclear testing and long- range rocket launches , all of which are a part of an " upcoming all - out action " aimed at the United States, " the sworn enemy of the Korean people . "
February 12 , 2013
THIRD NUCLEAR TEST
North Korea conducts its third underground nuclear test. This is the first nuclear test carried out under leader Kim Jong Un .
October 2 , 2014
More talks ?
A senior North Korean envoy says the country is ready to resume the six - party talks regarding its nuclear program .
May 6 , 2015
Capable of striking U. S . mainland
Park Yong Chol , deputy director of the DPRK Institute for Research into National Reunification , tells CNN in an exclusive interview that his country has the missile capability to strike mainland United States and would do so if the U. S. " forced their hand . "
May 9 , 2015
Submarine missile test
The North Korean state news agency reports that the country has carried out a successful underwater test of a ballistic missile by launching it from a submarine.
May 20 , 2015
Moving towards ICBMs ?
North Korea says that it has the ability to miniaturize nuclear weapons , a key step toward building nuclear missiles. A U. S. National Security Council spokesman responds that the U. S. does not think the North Koreans have that capability.
June 21 , 2015
No interest in Iran style talks
North Korea says it has no interest in Iran - style talks after an agreement reached between Tehran and Western powers . North Korea 's nuclear deterrent is " not a plaything to be put on the negotiating table , as it is the essential means to protect its sovereignty and vital rights from the U. S. nuclear threat and hostile policy which have lasted for more than half a century, " an official says .
August 12 , 2015
Report claims North Korea has new uranium enrichment facility
Analysts say satellite imagery indicates that a second hall housing active centrifuges used for uranium enrichment has been
opened at the Yongbyon nuclear site .
August 15, 2015 — August 24 , 2015
High tensions on the Korean peninsula
North and South Korea reach an agreement after a series of flashpoints bring military tensions on the peninsula to their highest point in years, including landmine blasts , loudspeakers blaring propaganda, an exchange of artillery fire and threats of more hostilities. North Korea agrees to lift a " semi - war state " declared during the emergency .
September 15 , 2015
Ready to use nuclear weapons at 'any time '
A North Korean senior atomic energy official says the country is
ready to attack the U. S. with nuclear weapons at " any time " , adding that its nuclear arsenal has imrpoved both " in quality and quantity " .
September 16 , 2015
Sanctions not enough '
U. S. Secretary of State John Kerry warns that North Korea must not be allowed to become a nuclear weapons state , even if it takes more than sanctions to convince them .
October 9 , 2015
Preparations for fourth test underway
U. S. officials tell CNN that there are " indications " that North Korea is preparing for a major weapons test, likely a submarine - launched medium - range ballistic missile .
October 10 , 2015
Huge military parade
North Korea holds a huge military parade to celebrate the 70 th anniversary of the ruling Workers ' Party, during which Kim Jong Un says his country is " fully ready " to defend itself against any U. S. threat .
January 6 , 2016
Hydrogen bomb test
North Korea claims that it successfully tested a thermonuclear device , a marked increase in its nuclear capabilities .
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A quick lesson in history
Atomic bombs have been only used twice in warfare -- both times by the United States and both times on Japan.
The devastation led to Japan's unconditional surrender and brought an end to the war.
Hydrogen bombs have never been used, although there have been times when the world seemed to be on the brink. The Cuban missile crisis in the 1960s is just one example.
Because of their devastating destructive potential, the nuclear powers are wary of using them. Nuclear treaties have rolled back nuclear warhead numbers in recent decades.
A quick look at the nuclear powers
Since dawn of the nuclear age, at least eight nations have conducted more than 2,000 nuclear test explosions.
The United States was the first one, detonating an atomic bomb in New Mexico on July 16, 1945. In the ensuing years, the U.S. has been joined by the USSR/Russia, United Kingdom, France, China, India, Pakistan and North Korea. Israel is also believed to have nuclear weapons.
There are believed to be 10,000 to 15,000 nuclear warheads in the arsenals of the nuclear powers.
North Korea is the only nation to have conducted any nuclear tests since 1999, with tests in 2006, 2009, 2013 and this year. India and Pakistan conducted nuclear tests in 1998.
How do North Korea's nuclear capabilities stack up?
It has not been confirmed that North Korea has successfully tested a miniaturized H-bomb.
Navias, for one, says he does not believe North Korea's claim.
"Their rhetoric tends to run ahead of their actual capabilities," he told CNN.
Wednesday's test yielded a blast of a similar magnitude to a previous North Korean test in 2013, he said.
"One would have expected the yield (from an H-bomb) to have been far greater."
Nevertheless, North Korea's advances in nuclear weapons technology were real and concerning, he said.
While Pyongyang does not have intercontinental ballistic missile technology that would enable it to strike the West Coast of the United States, it has missiles capable of striking South Korea, Japan and U.S. military bases in the region, he said.
North Korea still needs to make "very challenging" advancements in miniaturizing nuclear warheads to be able to fit them onto missiles, and to improve its missile guidance systems, he said. But it is undoubtedly making efforts to advance in these areas.
"There are people out there that know this stuff," he said.
It also claims to have recently tested a submarine-launched ballistic missile, he said -- a technology that, if mastered, "would be a completely different level of threat."
"I don't think they've reached anywhere with those things, but they're moving steadily in that direction and the outside world has little leverage," he said.
"If left unattended, it's not unreasonable to assume that in the long run, all these things will realize themselves."