A nuclear weapon is a type of explosive weapon that derives its destructive force from nuclear reactions of fission or a combination of fission and fusion. As a result, even a nuclear weapon with a small yield is significantly more powerful than the largest conventional explosives, and a single weapon is capable of destroying an entire city.
In the history of warfare, only two nuclear weapons have been detonated aggressively - both by the United States of America, during the closing days of World War II. The first was detonated on the morning of 6 August 1945, when the United States dropped a uranium gun-type device code-named "Little Boy" on the Japanese city of Hiroshima. The second was detonated three days later when the United States dropped a plutonium implosion-type device code-named "Fat Man" on the city of Nagasaki. These bombings resulted in the immediate deaths of around 120,000 people from injuries sustained from the explosion and acute radiation sickness, and even more deaths over time from long-term effects of radiation. The use of these weapons was and remains controversial. (See Atomic bombings of Hiroshima and Nagasaki for a full discussion.)
Since the Hiroshima and Nagasaki bombings, nuclear weapons have been detonated on over two thousand occasions for testing purposes and demonstration purposes. The only countries known to have detonated such weapons are (chronologically) the United States, the Soviet Union, the United Kingdom, France, the People's Republic of China, India, Pakistan, and North Korea.
Various other countries may hold nuclear weapons but have never publicly admitted possession, or their claims to possession have not been verified. For example, Israel has modern airborne delivery systems and appears to have an extensive nuclear program with hundreds of warheads (see Israel and weapons of mass destruction), officially maintains a policy of "ambiguity" with respect to its actual possession of nuclear weapons. According to some estimates, it possesses as many as 200 nuclear warheads. Iran currently stands accused by the United States of attempting to develop nuclear weapons capabilities, though its government states that its acknowledged nuclear activities, such as uranium enrichment, are for non-weapons purposes. South Africa also secretly developed a small nuclear arsenal, but disassembled it in the early 1990s. (For more information see List of states with nuclear weapons.)
Apart from their use as weapons, nuclear explosives have been tested and used for various non-military uses. Synthetic elements, such as einsteinium and fermium, created by neutron bombardment of uranium and plutonium during thermonuclear explosions, were discovered in the aftermath of the first hydrogen bomb test.
History
Main article: History of nuclear weapons
The aftermath of the atomic bombing of HiroshimaThe first nuclear weapons were created in the United States by an international team, including many displaced scientists from central Europe, which included Germany, with assistance from the United Kingdom and Canada during World War II as part of the top-secret Manhattan Project. While the first weapons were developed primarily out of fear that Nazi Germany would develop them first, they were eventually used against the Japanese cities of Hiroshima and Nagasaki. The first test was conducted on July 16, 1945 at a site near Alamogordo, New Mexico. The Soviet Union developed and tested their first nuclear weapon in 1949, based partially on information obtained from Soviet espionage in the United States. Both the U.S. and USSR would go on to develop weapons powered by nuclear fusion (hydrogen bombs) by the mid-1950s. With the invention of reliable rocketry during the 1960s, it became possible for nuclear weapons to be delivered anywhere in the world on a very short notice, and the two Cold War superpowers adopted a strategy of deterrence to maintain a shaky peace.
U.S. and USSR/Russian nuclear weapons stockpiles, 1945-2005Nuclear weapons were symbols of military and national power, and nuclear testing often used both to test new designs as well as to send political messages. Other nations also developed nuclear weapons during this time, including the United Kingdom, France, and China. These five members of the "nuclear club" agreed to attempt to limit the spread of nuclear proliferation to other nations, though four other countries (India, South Africa, Pakistan, and Israel) developed or acquired nuclear arms during this time. At the end of the Cold War in the early 1990s, the Russian Federation inherited the weapons of the former USSR, and along with the U.S., pledged to reduce their stockpile for increased international safety. Nuclear proliferation has continued, though, with Pakistan testing their first weapons in 1998, and North Korea performing a test in 2006. In January 2005, Pakistani metallurgist Abdul Qadeer Khan confessed to selling nuclear technology and information of nuclear weapons to Iran, Libya, and North Korea in a massive, international proliferation ring. On October 9, 2006, North Korea claimed it had conducted an underground nuclear test, though the very small apparent yield of the blast has led many to conclude that it was not fully successful (see 2006 North Korean nuclear test). Additionally, since 9/11 increased attention has been given to the threat of nuclear terrorism, whereby non-state actors manage to develop, purchase, or steal nuclear arms and detonate them against civilians. Post-Cold War discussions of nuclear weapons have focused on the fact that the "rationality" of nuclear deterrence, credited with the lack of use of nuclear weapons during the Cold War, may not apply in a world with only one superpower, or a world where the nuclear actors are stateless.
