Nuclear weapons
0513-nuclear-bomb-oil-spill_full_600.jpgThe Atomic Bomb
In an atomic bomb, the energy or force of the weapon is derived only from nuclear fission - the splitting of the nucleus of heavy elements such as plutonium or highly enriched uranium into lighter nuclei. The enormous amount of nuclear energy that is released by this process produces a large amount of heat and electricity.

Replicas of Fat Man and Little Boy, the two atomic bombs used on Japan during World War II

Los Alamos Labratory

Replicas of Fat Man and Little Boy, the two nuclear bombs dropped on Japan.

A nuclear weapon's explosive power is measured in yield, which is expressed in tons of TNT. Fission, or atomic bombs, can be as small as one kiloton (KT) of explosive power or as large as several hundred kilotons. This is in contrast to the much larger thermonuclear or hydrogen bombs, which can be a thousand times bigger than atomic bombs. They are expressed in millions of tons of TNT or megatons (MT).

The U.S. is the only country to have used an atomic bomb in war — the first, nicknamed Little Boy, was dropped on Hiroshima, Japan on Aug. 6, 1945 with a yield of 15 KT and the second, Fat Man, was dropped on Nagasaki, Japan on Aug. 9, 1945 with a yield of 20 KT.

However, over time atomic weapons, which basically followed the Nagasaki Fat Man design, began to get smaller and lighter with greater yield, becoming more efficient. Compact atomic bombs directed to hit a city directly could still cause casualties in the hundreds of thousands, if not millions.

Thermonuclear Weapons
Thermonuclear weapons, often referred to as Hydrogen bombs or H-bombs, are nuclear weapons in which their extreme explosive powers are obtained through the process of nuclear fusion - the process of forming a heavier nucleus from two lighter ones. (Nuclei of the hydrogen isotopes
A thermonuclear expolosion w88-nyt.jpg


A U.S. hydrogen bomb explosion in Eniwetok Atoll, Marshall Islands.

tritium or deuterium are fused.) This fusion requires incredibly high temperatures. They are nearly all achieved through the initial detonation of an atomic bomb.

Like atomic bombs, the explosion of an H-bomb produces a blast that can destroy structures within a radius of several miles, extreme heat that can spark firestorms and intense white light that can induce blindness. Radioactive fallout, or the release into the environment of highly unstable fragments or byproducts of fission such as cesium-137 and strontium-90, can poison living creatures and contaminate air, water and soil for hundreds of years.

These weapons can be thousands of times more powerful than atomic bombs and are measured in yield equal to megatons of TNT and yet they can be made small enough to fit in a ballistic missile warhead or an artillery shell that can be carried. In 1952, the U.S. was the first nation to successfully test a 10 MT fusion bomb. Although they can be much more destructive than atomic bombs, hydrogen bombs are also much more difficult to create.

Small thermonuclear weapons are called neutron bombs. Neutron bombs, also called enhanced radiation warheads, are weapons that can be used effectively against tank and infantry formations on a traditional battlefield yet won't impact nearby towns or cities within a few miles. They work by producing minimal blast and heat but releasing high amounts of radiation.Nuclear warfare strategy is a set of policies that deal with preventing or fighting a nuclear war. The policy of trying to prevent an 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 capability (the ability of a country to respond to a nuclear attack with one of its 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 above) allow for different types of nuclear strategies. The goals of any strategy are generally to make it difficult for an enemy to launch a pre-emptive strike against the weapon system and difficult to defend against the delivery of the weapon during a potential conflict. Sometimes this has meant keeping the weapon locations hidden, such as deploying them on submarines or rail cars whose locations are very hard for an enemy to track and other times this means protecting them by burying them in hardened bunkers.

Other components of nuclear strategies have included using missile defense (to destroy the missiles before they land) or implementation of civil defense measures (using early-warning systems to evacuate citizens to safe areas before an attack).

Note that weapons designed to threaten large populations, or to generally deter attacks are known as strategic weapons. Weapons designed for use on a battlefield in military situations are called 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 mutually 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. According to an advisory opinion issued by the International Court of Justice in 1996, the use of (or threat of use of) such weapons would generally be contrary to the rules of international law applicable in armed conflict, but the court did not reach an opinion as to whether or not the threat or use would be lawful in specific extreme circumstances such as if the survival of the state were at stake.
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission ("atomic") bomb test released the same amount of energy as approximately 20,000 tons of TNT. The first thermonuclear ("hydrogen") bomb test released the same amount of energy as approximately 10,000,000 tons of TNT.[1]
A modern thermonuclear weapon weighing little more than 2,400 pounds (1,100 kg) can produce an explosive force comparable to the detonation of more than 1.2 million tons (1.1 million tonnes) of TNT.[2] Thus, even a small nuclear device no larger than traditional bombs can devastate an entire city by blast, fire and radiation. Nuclear weapons are considered weapons of mass destruction, and their use and control have been a major focus of international relations policy since their debut.

Only two nuclear weapons have been used in the course of warfare, both by the United States near the end of World War II. On 6 August 1945, a uranium gun-type fission bomb code-named "Little Boy" was detonated over the Japanese city of Hiroshima. Three days later, on 9 August, a plutonium implosion-type fission bomb code-named "Fat Man" was exploded over Nagasaki, Japan. These two bombings resulted in the deaths of approximately 200,000 people—mostly civilians—from acute injuries sustained from the explosions.[3] The role of the bombings in Japan's surrender, and their ethical status, remain the subject of scholarly and popular debate.

Since the bombings of Hiroshima and Nagasaki, nuclear weapons have been detonated on over two thousand occasions for testing purposes and demonstrations. Only a few nations possess such weapons or are suspected of seeking them. The only countries known to have detonated nuclear weapons—and that acknowledge possessing such weapons—are (chronologically by date of first test) the United States, the Soviet Union (succeeded as a nuclear power by Russia), the United Kingdom, France, the People's Republic of China, India, Pakistan, and North Korea. In addition, Israel is also widely believed to possess nuclear weapons, though it does not acknowledge having them.[4][5][6] One state, South Africa, fabricated nuclear weapons in the past, but as its apartheid regime was coming to an end it disassembled its arsenal, acceded to the NPT and accepted full-scope international safeguards.[7]
The Federation of American Scientists estimates there are more than 17,000 nuclear warheads in the world as of 2012, with around 4,300 of them considered "operational", ready for use.[4]
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, and they are said to have done this during the Cold War between the U.S. and the Soviet Union.[18] Political scientist Kenneth Waltz is the most prominent advocate of this argument.[19][20]

The threat of potentially suicidal terrorists possessing nuclear weapons (a form of nuclear terrorism) complicates the decision process. The prospect of mutually assured destruction may not deter an enemy who expects to die in the confrontation. Further, if the initial act is from a stateless terrorist instead of a sovereign nation, there is no fixed nation or fixed military targets to retaliate against. It has been argued, especially after the September 11, 2001 attacks, that this complication is the sign of the next age of nuclear strategy, distinct from the relative stability of the Cold War.[21] In 1996, the United States adopted a policy of allowing the targeting of its nuclear weapons at terrorists armed with weapons of mass destruction.[22]
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. Additionally, development and maintenance of delivery options is among the most resource-intensive aspects of a nuclear weapons program: according to one estimate, deployment costs accounted for 57% of the total financial resources spent by the United States in relation to nuclear weapons since 1940.[17]

Historically the first method of delivery, and the method used in the two nuclear weapons used in warfare, was as a gravity bomb, dropped from bomber aircraft. This is usually the first method that countries developed, as it does not place many restrictions on the size of the weapon and weapon miniaturization requires considerable weapons design knowledge. It does, however, limit attack range, response time to an impending attack, and the number of weapons that a country can field at the same time.
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 free-fall gravity bombs, namely the B61.[8]
A Trident II SLBM launched from a Royal Navy Vanguard class ballistic missile submarine.
More preferable from a strategic point of view is a nuclear weapon mounted onto a missile, which can use a ballistic trajectory to deliver the warhead over the horizon. While even short range missiles allow for a faster and less vulnerable attack, the development of long-range intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs) has given some nations the ability 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), can launch multiple warheads at different targets from one missile, reducing the chance of a 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 difficult.[8]

Tactical weapons 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 of combining sufficient yield with portability limits their military utility.[8]

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