Produced by the Monterey Institute's James Martin Center for Nonproliferation Studies

Updated January 2010

The United Nations (UN) has 192 member countries, but only eight are known or widely considered to have nuclear weapons. In order of their acquisition of nuclear weapons, these countries are as follows:

• United States (first test, 1945)
• Russia (first test, 1949)
• United Kingdom (first test, 1952)
• France (first test, 1960)
• China (first test, 1964)
• India (first test, 1974)
• Pakistan (first test, 1998)

Most countries believe Israel possesses nuclear weapons, but it has never officially acknowledged possession and is not known to have conducted a nuclear test. Unclassified studies claim Israel achieved a nuclear capability in the mid-1960s, and may currently possess anywhere between 100 and 300 nuclear warheads. The United States believes that North Korea possesses enough separated plutonium for at least eight nuclear weapons and possibly is working to produce weapons-grade uranium. On October 9, 2006, North Korea announced that it had tested a nuclear device. Seismic monitoring reported a explosion of less than one kiloton, very small for a nuclear test; North Korea had warned China that it planned to test a four-kiloton bomb. Air sampling showed that North Korea tried to explode a plutonium bomb. In February 2007, North Korea agreed to suspend its nuclear program in exchange for financial and diplomatic aid from the United States, South Korea, China, and Russia. However, on May 25, 2009, North Korea tested another nuclear device with more explosive power than the device tested in 2006. Given the seismic readings following the event, experts estimate that the latest test had an explosive yield of 3 to 8 kilotons.

The "Superpowers." The United States and Russia possess massive nuclear arsenals. Each side continues to deploy thousands of strategic nuclear warheads. Strategic warheads are those placed on long-range delivery systems, specifically intercontinental ballistic missiles (ICBM=range greater than 5,500 kilometers), ballistic missile submarines, and long-range bombers. In addition, both sides possess large numbers of non-strategic or tactical nuclear weapons. These weapons are deployed on shorter-range delivery systems, such as on air-launched cruise missiles. It is unclear how many tactical nuclear weapons each country deploys. Both countries have many thousands of undeployed nuclear weapons in reserve.

Atomic and Hydrogen Bombs. The United States and Russia first developed fission or atomic bombs. This was the type of weapon the United States used on Hiroshima and Nagasaki. The yields of fission weapons are measured in kilotons. A kiloton equals one thousand tons of TNT. For instance, the devices that destroyed Nagasaki and Hiroshima had yields of 20 kilotons and 13 kilotons, respectively. Then, in the early 1950s, the two countries developed far more powerful thermonuclear weapons or hydrogen bombs. Thermonuclear weapons have been tested with yields measuring megatons. A megaton equals one million tons of TNT. The largest ever thermonuclear bomb was tested by Russia in 1961. It had a yield of 50 megatons, nearly 5,000 times more powerful than the Hiroshima bomb.

The Smaller Nuclear Arsenals. The nuclear arsenals of Great Britain, France, and China each number in the hundreds of weapons. These arsenals also include thermonuclear weapons. Great Britain's nuclear weapons are deployed on ballistic missile submarines. France's nuclear weapons are deployed on both ballistic missile submarines and bombers. China relies principally on land-based ballistic missiles. China is thought to have a very small number of missiles, estimated between 18 and 24, which can reach the United States.

South Africa secretly manufactured nuclear weapons in the 1970s and 1980s. In 1990, however, it dismantled its nuclear weapons program. South Africa finally joined the Nuclear Non-Proliferation Treaty (NPT) as a non-nuclear weapon state in 1991, and disclosed its earlier nuclear weapons program in 1993. It then placed all of its nuclear weapon materials under international inspection to ensure that they are not used again for nuclear arms.