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A 23 kiloton tower shot called BADGER, fired on April 18, 1953 at the Nevada Test Site, as part of the Operation Upshot-Knothole nuclear test series.

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A nuclear explosion occurs as a result of the rapid release of energy from an intentionally high-acceleration nuclear reaction. The driving reaction may be nuclear fission, nuclear fusion or a multistage cascading combination of the two, though to date all fusion based weapons have used a fission device to initiate fusion, and a pure fusion weapon remains a hypothetical device.

Atmospheric nuclear explosions are associated with "mushroom clouds" although mushroom clouds can occur with large chemical explosions and it is possible to have an air burst nuclear explosion without these clouds. Atmospheric nuclear explosions produce large amounts of radiation and radioactive debris.

In 1963, all nuclear and many non-nuclear states signed the Limited Test Ban Treaty, pledging to refrain from testing nuclear weapons in the atmosphere, underwater, or in outer space. The treaty permitted underground tests.

The primary application to date has been military (i.e. nuclear weapons). However, there are other potential applications, which have not yet been explored, or have been considered but abandoned. They include:

• Nuclear pulse propulsion, including using a nuclear explosion as asteroid deflection strategy.
• Power generation; see PACER
• Peaceful nuclear explosions

The following list is of milestone nuclear explosions. In addition to the atomic bombings of Hiroshima and Nagasaki, the first nuclear test of a given weapon type for a country is included, and tests which were otherwise notable (such as the largest test ever). All yields (explosive power) are given in their estimated energy equivalents in kilotons of TNT (see megaton).

Date	Name	Yield (kT)	Country	Significance
Jul 16 1945	Trinity	19	USA	First fission device test
Aug 6 1945	Little Boy	15	USA	Bombing of Hiroshima, Japan
Aug 9 1945	Fat Man	21	USA	Bombing of Nagasaki, Japan
Aug 29 1949	Joe 1	22	USSR	First fission weapon test by the USSR
Oct 3 1952	Hurricane	25	UK	First fission weapon test by the UK
Nov 1 1952	Ivy Mike	10,400	USA	First "staged" thermonuclear weapon test (not deployable)
Aug 12 1953	Joe 4	400	USSR	First fusion weapon test by the USSR (not "staged", but deployable)
Mar 1 1954	Castle Bravo	15,000	USA	First deployable "staged" thermonuclear weapon; fallout accident
Nov 22 1955	RDS-37	1,600	USSR	First "staged" thermonuclear weapon test by the USSR (deployable)
Nov 8 1957	Grapple X	1,800	UK	First (successful) "staged" thermonuclear weapon test by the UK
Feb 13 1960	Gerboise Bleue	70	France	First fission weapon test by France
Oct 31 1961	Tsar Bomba	50,000	USSR	Largest thermonuclear weapon ever tested
Oct 16 1964	596	22	PR China	First fission weapon test by the People's Republic of China
Jun 17 1967	Test No. 6	3,300	PR China	First "staged" thermonuclear weapon test by the People's Republic of China
Aug 24 1968	Canopus	2,600	France	First "staged" thermonuclear test by France
May 18 1974	Smiling Buddha	12	India	First fission nuclear explosive test by India
May 11 1998	Shakti I	43	India	First potential fusion/boosted weapon test by India (exact yields disputed, between 25kt and 45kt)
May 11 1998	Shakti II	12	India	First deployable fission weapon test by India
May 28 1998	Chagai-I	9-12	Pakistan	First fission weapon test by Pakistan. First nuclear test ever to be carried out inside a mountain. See video of test: http://youtube.com/watch?v=QBu1NkRHtZk&feature=related
May 30 1998	Kharan-I	4-6	Pakistan	Second fission weapon test by Pakistan
Oct 9 2006	Hwadae-ri	<1	North Korea	First fission device tested by North Korea

"Deployable" refers to whether the device tested could be hypothetically used in actual combat (in contrast with a proof-of-concept device). "Staging" refers to whether it was a "true" hydrogen bomb of the so-called Teller-Ulam configuration or simply a form of a boosted fission weapon. For a more complete list of nuclear test series, see List of nuclear tests. Some exact yield estimates, such as that of the Tsar Bomba and the tests by India and Pakistan in 1998, are somewhat contested among specialists.

Main article: Peaceful nuclear explosions

The 1965 Chagan nuclear test in the Soviet Union was used to create a dam on the Semipalatinsk river

Peaceful nuclear explosions (PNEs) are nuclear explosions conducted for non-military purposes, such as activities related to economic development including the creation of canals. During the 1960s and 1970s, both the United States and the Soviet Union conducted a number of PNEs.Six of the explosions by the Soviet Union are considered to have been of an applied nature, not just tests.

Subsequently the United States and the Soviet Union halted their programs. Definitions and limits are covered in the Peaceful Nuclear Explosions Treaty of 1976.

See also: Operation Plowshare and Nuclear Explosions for the National Economy

Main articles: Nuclear weapons and History of nuclear weapons

In the history of warfare, two nuclear weapons have been detonated — both by the United States, during the closing days of World War II. The first event occurred 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 event occurred three days later when, again, 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 and even more over time. The use of these weapons was and remains controversial. (See Atomic bombings of Hiroshima and Nagasaki for a full discussion).

Main article: Nuclear testing

Nuclear tests are experiments carried out to determine the effectiveness, yield and explosive capability of nuclear weapons. Throughout the twentieth century, most nations that have developed nuclear weapons have staged tests of them. Testing nuclear weapons can yield information about how the weapons work, as well as how the weapons behave under various conditions and how structures behave when subjected to nuclear explosions. Additionally, nuclear testing has often been used as an indicator of scientific and military strength, and many tests have been overtly political in their intention; most nuclear weapons states publicly declared their nuclear status by means of a nuclear test.

Main article: Effects of nuclear explosions

The dominant effects of a nuclear weapon (the blast and thermal radiation) are the same physical damage mechanisms as conventional explosives, but the energy produced by a nuclear explosive is millions of times more per gram and the temperatures reached are in the tens of millions of degrees.