A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion reactions, producing a nuclear explosion. Both bomb types release large quantities of energy from relatively small amounts of matter.
Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate. There are three existing basic design types:
Building on major scientific breakthroughs made during the 1930s, the United Kingdom began the world's first nuclear weapons research project, codenamed Tube Alloys, in 1941, during World War II. The United States, in collaboration with the United Kingdom, initiated the Manhattan Project the following year to build a weapon using nuclear fission. The project also involved Canada. In August 1945, the atomic bombings of Hiroshima and Nagasaki were conducted by the United States, with British consent, against Japan at the close of that war, standing to date as the only use of nuclear weapons in hostilities.
Nuclear weapons tests are experiments carried out to determine the performance, yield, and effects of nuclear weapons. Testing nuclear weapons offers practical information about how the weapons function, how detonations are affected by different conditions, and how personnel, structures, and equipment are affected when subjected to nuclear explosions. However, nuclear testing has often been used as an indicator of scientific and military strength. Many tests have been overtly political in their intention; most nuclear weapons states publicly declared their nuclear status through a nuclear test.
The nuclear arms race was an arms race competition for supremacy in nuclear warfare between the United States, the Soviet Union, and their respective allies during the Cold War. During this same period, in addition to the American and Soviet nuclear stockpiles, other countries developed nuclear weapons, though no other country engaged in warhead production on nearly the same scale as the two superpowers.
The United States is known to have possessed three types of weapons of mass destruction: nuclear, chemical, and biological weapons. The U.S. is the only country to have used nuclear weapons on another country, when it detonated two atomic bombs over two Japanese cities of Hiroshima and Nagasaki during World War II. It had secretly developed the earliest form of the atomic weapon during the 1940s under the title "Manhattan Project". The United States pioneered the development of both the nuclear fission and hydrogen bombs. It was the world's first and only nuclear power for four years, from 1945 until 1949, when the Soviet Union produced its own nuclear weapon. The United States has the second-largest number of nuclear weapons in the world, after the Russian Federation.
France is one of the five "Nuclear Weapons States" under the Treaty on the Non-Proliferation of Nuclear Weapons, but is not known to possess or develop any chemical or biological weapons. France is the only member of the European Union to possess independent (non-NATO) nuclear weapons. France was the fourth country to test an independently developed nuclear weapon, doing so in 1960 under the government of Charles de Gaulle. The French military is currently thought to retain a weapons stockpile of around 300 operational (deployed) nuclear warheads, making it the fourth-largest in the world, speaking in terms of warheads, not megatons. The weapons are part of the national Force de frappe, developed in the late 1950s and 1960s to give France the ability to distance itself from NATO while having a means of nuclear deterrence under sovereign control.
India possesses nuclear weapons and previously developed chemical weapons. Although India has not released any official statements about the size of its nuclear arsenal, recent estimates suggest that India has 170 nuclear weapons and has produced enough weapons-grade plutonium for up to 200 nuclear weapons. In 1999, India was estimated to have 800 kilograms (1,800 lb) of separated reactor-grade plutonium, with a total amount of 8,300 kilograms (18,300 lb) of civilian plutonium, enough for approximately 1,000 nuclear weapons. India has conducted nuclear weapons tests in a pair of series namely Pokhran I and Pokhran II.
The B61 nuclear bomb is the primary thermonuclear gravity bomb in the United States Enduring Stockpile following the end of the Cold War. It is a low-to-intermediate yield strategic and tactical nuclear weapon featuring a two-stage radiation implosion design.
The United States was the first country to manufacture nuclear weapons and is the only country to have used them in combat, with the bombings of Hiroshima and Nagasaki in World War II. Before and during the Cold War, it conducted 1,054 nuclear tests, and tested many long-range nuclear weapons delivery systems.
Pokhran-II was a series of five nuclear weapon tests conducted by India in May 1998. The bombs were detonated at the Indian Army's Pokhran Test Range in Rajasthan. It was the second instance of nuclear testing conducted by India, after the first test, code-named Smiling Buddha, was conducted in May 1974.
A thermonuclear weapon, fusion weapon or hydrogen bomb (H bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lower mass, or a combination of these benefits. Characteristics of nuclear fusion reactions make possible the use of non-fissile depleted uranium as the weapon's main fuel, thus allowing more efficient use of scarce fissile material such as uranium-235 or plutonium-239. The first full-scale thermonuclear test was carried out by the United States in 1952 and the concept has since been employed by most of the world's nuclear powers in the design of their weapons.
The explosive yield of a nuclear weapon is the amount of energy released such as blast, thermal, and nuclear radiation, when that particular nuclear weapon is detonated, usually expressed as a TNT equivalent (the standardized equivalent mass of trinitrotoluene which, if detonated, would produce the same energy discharge), either in kilotonnes (kt—thousands of tonnes of TNT), in megatonnes (Mt—millions of tonnes of TNT), or sometimes in terajoules (TJ). An explosive yield of one terajoule is equal to 0.239 kilotonnes of TNT. Because the accuracy of any measurement of the energy released by TNT has always been problematic, the conventional definition is that one kilotonne of TNT is held simply to be equivalent to 1012 calories.
Project 596 was the first nuclear weapons test conducted by the People's Republic of China, detonated on 16 October 1964, at the Lop Nur test site. It was a uranium-235 implosion fission device made from weapons-grade uranium (U-235) enriched in a gaseous diffusion plant in Lanzhou.
Gerboise Bleue was the codename of the first French nuclear test. It was conducted by the Nuclear Experiments Operational Group (GOEN), a unit of the Joint Special Weapons Command on 13 February 1960, at the Saharan Military Experiments Centre near Reggane, French Algeria in the Sahara desert region of Tanezrouft, during the Algerian War. General Pierre Marie Gallois was instrumental in the endeavour, and earned the nickname of père de la bombe A.
The State of Israel is widely believed to possess nuclear weapons. Estimates of Israel's stockpile range between 90 and 400 nuclear warheads, and the country is believed to possess the ability to deliver them in several methods, including by aircraft, as submarine-launched cruise missiles, and via the Jericho series of intermediate to intercontinental range ballistic missiles. Its first deliverable nuclear weapon is thought to have been completed in late 1966 or early 1967; which would make it the sixth country in the world to have developed them.
The application of nuclear technology, both as a source of energy and as an instrument of war, has been controversial.
