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Nuclear weapon

2007 Schools Wikipedia Selection. Related subjects: Military History and War


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   The mushroom cloud of the atomic bombing of Nagasaki, Japan, 1945, rose
   some 18 kilometers (11 mi) above the hypocenter.
   Enlarge
   The mushroom cloud of the atomic bombing of Nagasaki, Japan, 1945, rose
   some 18 kilometers (11 mi) above the hypocenter.

                                                           Nuclear weapons
                                          One of the first nuclear bombs.
                                             History of nuclear weapons
                                                  Nuclear warfare
                                                 Nuclear arms race
                                              Weapon design / testing
                                                 Nuclear explosion
                                                  Delivery systems
                                                 Nuclear espionage
                                                   Proliferation
                                                                    States
                                                  Nuclear weapons states

                                              US · Russia · UK · France
                                                China · India · Pakistan
                                                     Israel · North Korea

   A nuclear weapon is a weapon which derives its destructive force from
   nuclear reactions of fission or fusion. As a result, even a nuclear
   weapon with a relatively 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, nuclear weapons have been used only twice,
   both during the closing days of World War II. The first event occurred
   on the morning of August 6, 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 the
   United States dropped a plutonium implosion-type device code-named "
   Fat Man" on the city of Nagasaki. The use of these weapons, which
   resulted in the immediate deaths of around 100,000 to 200,000 people
   and even more over time, was and remains controversial — critics around
   the world charged that they were unnecessary acts of mass killing,
   while others claimed that they ultimately reduced casualties on both
   sides by hastening the end of the war. This topic has seen increased
   debate recently in the wake of increased terrorism involving killings
   of civilians by both state and non-state players, with parties claiming
   that the end justifies the means (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 and demonstration
   purposes. The only countries known to have detonated such weapons are
   (chronologically) the United States, Soviet Union, United Kingdom,
   France, 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), though it
   officially maintains a policy of "ambiguity" with respect to its actual
   possession of nuclear weapons. Iran currently stands accused by a
   number of governments of attempting to develop nuclear capabilities,
   though its government claims that its acknowledged nuclear activities,
   such as uranium enrichment, are for peaceful purposes. South Africa
   also secretly developed a small nuclear arsenal, but disassembled it in
   the early 1990s. (For more information see List of countries with
   nuclear weapons.)

   Apart from their use as weapons, nuclear explosives have been tested
   and used for various non-military uses.

History

   The aftermath of the atomic bombing of Hiroshima.
   Enlarge
   The aftermath of the atomic bombing of Hiroshima.

   The first nuclear weapons were created in the United States, by an
   international team including many displaced émigré scientists from
   central Europe 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 in August 1945. 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, 1945-2005.
   Enlarge
   U.S. and USSR/Russian nuclear weapons stockpiles, 1945-2005.

   Nuclear weapons were symbols of military and national power, and
   nuclear testing was 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 at least three
   other countries (India, South Africa, Pakistan, and most likely Israel)
   developed 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).

   Nuclear weapons have been at the heart of many national and
   international political disputes and have played a major part in
   popular culture since their dramatic public debut in the 1940s and have
   usually symbolized the ultimate ability of mankind to utilize the
   strength of nature for destruction.

   There have been (at least) four major false alarms, the most recent in
   1995, that almost resulted in the U.S. or USSR/Russia launching its
   weapons in retaliation for a supposed attack. Additionally, during the
   Cold War the U.S. and USSR came close to nuclear warfare several times,
   most notably during the Cuban Missile Crisis. As of 2005, there are
   estimated to be at least 29,000 nuclear weapons held by at least eight
   countries, 96 percent of them in the possession of the United States
   and Russia.

Types of nuclear weapons

   The two basic fission weapon designs.
   Enlarge
   The two basic fission weapon designs.

   There are two basic types of nuclear weapons. The first are weapons
   which produce their explosive energy through nuclear fission reactions
   alone. These are known colloquially as atomic bombs, A-bombs, or
   fission bombs. In fission weapons, a mass of fissile material (
   enriched uranium or plutonium) is assembled into a supercritical
   mass—the amount of material needed to start an exponentially growing
   nuclear chain reaction—either by shooting one piece of subcritical
   material into another, or by compressing a subcritical mass with
   chemical explosives, at which point neutrons are injected and the
   reaction begins. A major challenge in all nuclear weapon designs is
   ensuring that a significant fraction of the fuel is consumed before the
   weapon destroys itself. The amount of energy released by fission bombs
   can range between the equivalent of less than a ton of TNT upwards to
   around 500,000 tons (500 kilotons) of TNT.

   The second basic type of nuclear weapon produces a large amount of its
   energy through nuclear fusion reactions, and can be over a thousand
   times more powerful than fission bombs. These are known as hydrogen
   bombs, H-bombs, thermonuclear bombs, or fusion bombs. Only six
   countries— United States, Russia, United Kingdom, People's Republic of
   China, France, and possibly India—are known to possess hydrogen bombs.
   Hydrogen bombs work by utilizing the Teller-Ulam design, in which a
   fission bomb is detonated in a specially manufactured compartment
   adjacent to a fusion fuel. The gamma and X-rays of the fission
   explosion compress and heat a capsule of tritium, deuterium, or lithium
   deuteride starting a fusion reaction. Neutrons emitted by this fusion
   reaction can induce a final fission stage in a depleted uranium tamper
   surrounding the fusion fuel, increasing the yield considerably as well
   as the amount of nuclear fallout. Each of these components is known as
   a "stage", with the fission bomb as the "primary" and the fusion
   capsule as the "secondary". By chaining together numerous stages with
   increasing amounts of fusion fuel, thermonuclear weapons can be made to
   an almost arbitrary yield; the largest ever detonated (the Tsar Bomba
   of the USSR) released an energy equivalent to over 50 million tons (
   megatons) of TNT, though most modern weapons are nowhere near that
   large.

   There are other types of nuclear weapons as well. For example, a
   boosted fission weapon is a fission bomb which increases its explosive
   yield through a small amount of fusion reactions, but it is not a
   hydrogen bomb. Some weapons are designed for special purposes; a
   neutron bomb is a nuclear weapon that yields a relatively small
   explosion but a relatively large amount of prompt radiation; these
   could theoretically be used to cause massive casualties while leaving
   infrastructure mostly intact. The detonation of a nuclear weapon is
   accompanied by a blast of neutron radiation. Surrounding a nuclear
   weapon with suitable materials (such as cobalt or gold) creates a
   weapon known as a salted bomb. This device can produce exceptionally
   large quantities of radioactive contamination. Most variety in nuclear
   weapon design is in different yields of nuclear weapons for different
   types of purposes, and in manipulating design elements to attempt to
   make weapons extremely small.

Nuclear strategy

   The United States' Peacekeeper missile was a MIRVed delivery system.
   Each missile could contain up to ten nuclear warheads (shown in red),
   each of which could be aimed at a different target. These were
   developed to make missile defense very difficult for an enemy country.
   Enlarge
   The United States' Peacekeeper missile was a MIRVed delivery system.
   Each missile could contain up to ten nuclear warheads (shown in red),
   each of which could be aimed at a different target. These were
   developed to make missile defense very difficult for an enemy country.

   Nuclear warfare strategy is a way for either fighting or avoiding a
   nuclear war. The policy of trying to ward off a potential attack by a
   nuclear weapon from another country by threatening nuclear retaliation
   is known as the strategy of nuclear deterrence. The goal in deterrence
   is to always maintain a second strike status (the ability to respond to
   a nuclear attack against your country with a nuclear attack of your
   own) and potentially to strive for first strike status (the ability to
   completely destroy an enemy's nuclear forces before they could
   retaliate). During the Cold War, policy and military theorists in
   nuclear-enabled countries worked out models of what sorts of policies
   could prevent one from ever being attacked by a nuclear weapon.

   Different forms of nuclear weapons delivery (see below) allow for
   different types of nuclear strategy, primarily by making it difficult
   to defend against them and difficult to launch a pre-emptive strike
   against them. Sometimes this has meant keeping the weapon locations
   hidden, such as putting them on submarines or train cars whose
   locations are very hard for an enemy to track, and other times this
   means burying them in hardened bunkers. Other responses have included
   attempts to make it seem likely that the country could survive a
   nuclear attack, by using missile defense (to destroy the missiles
   before they land) or by means of civil defense (using early warning
   systems to evacuate citizens to a safe area before an attack). Note
   that weapons which are designed to threaten large populations or to
   generally deter attacks are known as "strategic" weapons. Weapons which
   are designed to actually be used on a battlefield in military
   situations are known as "tactical" weapons.

   There are critics of the very idea of "nuclear strategy" for waging
   nuclear war who have suggested that a nuclear war between two nuclear
   powers would result in mutual annihilation. From this point of view,
   the significance of nuclear weapons is purely to deter war because any
   nuclear war would immediately escalate out of mutual distrust and fear,
   resulting in mutual assured destruction. This threat of national, if
   not global, destruction has been a strong motivation for anti-nuclear
   weapons activism.

   Critics from the peace movement and within the military establishment
   have questioned the usefulness of such weapons in the current military
   climate. The use of (or threat of use of) such weapons would generally
   be contrary to the rules of international law applicable in armed
   conflict, according to an Advisory opinion issued by the International
   Court of Justice in 1996.

   Perhaps the most controversial idea in nuclear strategy is that nuclear
   proliferation would be desirable. This view argues that unlike
   conventional weapons nuclear weapons successfully deter all-out war
   between states, as they did during the Cold War between the U.S. and
   the Soviet Union. Political scientist Kenneth Waltz is the most
   prominent advocate of this argument

Weapons delivery

   The first nuclear weapons were gravity bombs, such as the "Fat Man"
   weapon dropped on Nagasaki, Japan. These weapons were very large and
   could only be delivered by a bomber aircraft.
   Enlarge
   The first nuclear weapons were gravity bombs, such as the " Fat Man"
   weapon dropped on Nagasaki, Japan. These weapons were very large and
   could only be delivered by a bomber aircraft.

   Nuclear weapons delivery—the technology and systems used to bring a
   nuclear weapon to its target—is an important aspect of nuclear weapons
   relating both to nuclear weapon design and nuclear strategy.

   Historically the first method of delivery, and the method used in the
   two nuclear weapons actually used in warfare, is as a gravity bomb,
   dropped from bomber aircraft. This method is usually the first
   developed by countries as it does not place many restrictions on the
   size of the weapon, and weapon miniaturization is something which
   requires considerable weapons design knowledge. It does, however, limit
   the range of attack, the response time to an impending attack, and the
   number of weapons which can be fielded at any given time. Additionally,
   specialized delivery systems are usually not necessary; especially with
   the advent of miniaturization, nuclear bombs can be delivered by both
   strategic bombers and tactical fighter-bombers, allowing an air force
   to use its current fleet with little or no modification. This method
   may still be considered the primary means of nuclear weapons delivery;
   the majority of U.S. nuclear warheads, for example, are represented in
   free-fall gravity bombs, namely the B61.

   More preferable from a strategic point of view are nuclear weapons
   mounted onto a missile, which can use a ballistic trajectory to deliver
   a warhead over the horizon. While even short range missiles allow for a
   faster and less vulnerable attack, the development of intercontinental
   ballistic missiles (ICBMs) and submarine-launched ballistic missiles
   (SLBMs) has allowed some nations to plausibly deliver missiles anywhere
   on the globe with a high likelihood of success. More advanced systems,
   such as multiple independently targetable reentry vehicles (MIRVs)
   allow multiple warheads to be launched at several targets from any one
   missile, reducing the chance of any successful missile defense. Today,
   missiles are most common among systems designed for delivery of nuclear
   weapons. Making a warhead small enough to fit onto a missile, though,
   can be a difficult task.

   Tactical weapons (see above) have involved the most variety of delivery
   types, including not only gravity bombs and missiles but also artillery
   shells, land mines, and nuclear depth charges and torpedoes for
   anti-submarine warfare. An atomic mortar was also tested at one time by
   the United States. Small, two-man portable tactical weapons (somewhat
   misleadingly referred to as suitcase bombs), such as the Special Atomic
   Demolition Munition, have been developed, although the difficulty to
   combine sufficient yield with portability limits their military
   utility.
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