The Deadly Weapon In Human History

Nuclear weapon is any weapon that gets its destructive power from the transformation of matter in atoms into energy. All nuclear weapons are explosive devices. They include missiles, bombs, artillery shells, mines, and torpedoes. The most powerful nuclear weapons are far more destructive than any conventional (nonnuclear) weapon. Nuclear weapons often have been called atomic bombs and hydrogen bombs.

Nuclear weapons consist of fission weapons, also called atomic weapons, and thermonuclear weapons, which are also known as hydrogen weapons or fusion weapons. In fission weapons, matter is changed into energy when the nuclei (cores) of certain kinds of uranium or plutonium atoms are split. In thermonuclear weapons, matter is converted into energy when pairs of certain kinds of hydrogen nuclei combine to form a single nucleus. In general, thermonuclear weapons are much more powerful than fission weapons. Today, a large majority of nuclear weapons are thermonuclear devices.

The first nuclear weapons were two fission bombs used by the United States during World War II (1939-1945). In the war, one was dropped on each of the Japanese cities of Hiroshima and Nagasaki. The terrible destruction caused by the bombs became a major factor in Japan's decision to surrender to the United States and its Allies. Japan's surrender ended the war. The Hiroshima bomb caused the greater destruction. It killed from 70,000 to 100,000 people and destroyed approximately 5 square miles (13 square kilometers) of the city. About 13,000 short tons (12,000 metric tons) of TNT would have been required to produce the same amount of damage. Most of today's large thermonuclear weapons are about 8 to 40 times as powerful as the Hiroshima bomb.

The bombs exploded at Hiroshima and Nagasaki are the only two nuclear weapons that have ever been used. Since the end of World War II, however, nuclear weapons have dominated the military planning of the world's most powerful nations. Until 1991, two countries--the United States and the Soviet Union--had most of the world's nuclear weapons. In 1991, the Soviet Union was dissolved, and its republics became independent. Most Soviet nuclear weapons were located in the former republics of Belarus, Kazakhstan, Russia, and Ukraine. These republics agreed in 1992 that all nuclear weapons would be turned over to Russia. Other countries that possess nuclear arms include the United Kingdom, France, and China. Several other nations may have the ability to build nuclear weapons.

Most experts believe that, since the end of World War II, the threat of nuclear war probably has helped keep the peace between the world's major nations. However, all experts agree that extensive use of large nuclear weapons would cause heavy damage to many nations. Nations have long sought ways to control nuclear weapons and reduce the risk of nuclear war.

How nuclear weapons work

Fission weapons get their destructive power from the fission (splitting) of atomic nuclei. Only three kinds of atoms are known to be suitable for fissioning in such weapons. These atoms are of the uranium (U) isotopes U-235 and U-238 and of the plutonium (Pu) isotope Pu-239. Isotopes are different kinds of atoms of the same element. Each kind has a different mass.

Nuclear fission occurs when a neutron--a subatomic particle with no electric charge--strikes the nucleus of a uranium or plutonium atom. When the nucleus splits, a small amount of its matter is transformed into a large amount of energy. In addition, two or three additional neutrons are released. These neutrons may then split other nuclei. If this process continues, a self-sustaining chain reaction forms in which each split nucleus provides the means of splitting other nuclei. Such a chain reaction will cause a fission explosion.

The formation of a self-sustaining chain reaction requires a certain minimum mass of fissionable material.

This mass is known as the critical mass. A mass too small to support a self-sustaining chain reaction is called a subcritical mass.

Fission weapons use either of two basic methods to create a critical mass: (1) the gun-type method or (2) the implosion method. In the gun-type method, two subcritical pieces of material are placed in a device similar to the barrel of an artillery gun. One of the pieces rests at one end of the barrel. The other is put some distance from the first piece, with a powerful conventional explosive packed behind it. The barrel is sealed at both ends. When the weapon's fuse is triggered, the conventional explosive propels the second subcritical mass at a very high speed into the first. The resulting combined mass immediately becomes supercritical (greater than critical), causing a rapid, self-sustaining chain reaction, and thus a nuclear explosion. The United States used a gun-type fission bomb at Hiroshima.

In the implosion method, a subcritical mass is made supercritical by compressing it into a smaller volume. The subcritical mass, which is ball-shaped, is placed in the center of the weapon. The mass is surrounded by a spherical arrangement of conventional explosives. When the weapon's fuse is triggered, all the conventional explosives go off at the same time. The explosions compress the mass into a high-density supercritical mass. A self-sustaining chain reaction then takes place, and the explosion occurs. The United States used an implosion-type fission bomb at Nagasaki.

Thermonuclear weapons get their power from the fusion (combining) of atomic nuclei under intense heat. The nuclei fused in thermonuclear weapons are of the hydrogen isotopes deuterium and tritium.

Fusion reactions require temperatures equal to, or greater than, those found in the sun's core--about 27,000,000° F., or 15,000,000° C. The only practical way to achieve such temperatures is by means of a fission explosion. Thus, thermonuclear explosions are triggered by an implosion-type fission device. When the fission device explodes, it also releases neutrons that bombard a compound inside the weapon. This compound, called lithium-6 deuteride, consists of deuterium and lithium-6, an isotope of the element lithium. When struck by the released neutrons, the lithium-6 forms helium and tritium. Then, pairs of tritium nuclei, pairs of deuterium nuclei, and pairs of one tritium nucleus and one deuterium nucleus each fuse to form helium nuclei. A small amount of matter from each deuterium and tritium nucleus is converted into a large amount of energy, and a thermonuclear explosion occurs. The yield (explosive power) of a thermonuclear weapon can be increased by surrounding the lithium-6 deuteride with a blanket of the uranium isotope U-238. The U-238 undergoes fissioning in the course of the hydrogen explosion.

Effects of nuclear weapons

Nuclear explosive devices can have a wide variety of yields. Some older bombs had yields of about 20 megatons, or 1,540 Hiroshima bombs. A megaton is the amount of energy released by 1 million short tons (907,000 metric tons) of TNT. Today, most nuclear devices have yields of less than 1 megaton.

The effects that a nuclear explosion has on people, buildings, and the environment can vary greatly, depending on a number of factors. These factors include weather, terrain, the point of explosion in relation to the earth's surface, and the weapon's yield. This section describes the possible effects of a large nuclear weapon. The weapon's explosion would produce four basic effects: (1) a blast wave, (2) thermal radiation, (3) initial nuclear radiation, and (4) residual nuclear radiation.

Blast wave. The explosion begins with the formation of a fireball, which consists of a cloud of dust and of extremely hot gases under very high pressure. A fraction of a second after the explosion, the gases begin to expand and form a blast wave, also called a shock wave. This wave moves rapidly away from the fireball like a moving wall of highly compressed air. The blast wave created by a 1-megaton explosion could travel about 12 miles (19 kilometers) from ground zero in the first 50 seconds after the explosion. Ground zero is the point on the ground directly below the explosion.

The blast wave causes most of the damage that results from the explosion. As the wave moves forward, it creates overpressure, which is atmospheric pressure above the normal level. A 1-megaton explosion can produce enough overpressure to destroy most buildings within 1 mile (1.6 kilometers) of ground zero. The overpressure from such an explosion also can cause moderate to severe damage to buildings within 6 miles (9.6kilometers) of ground zero. The blast wave also is accompanied by strong winds. These winds may reach speeds of 400 miles (640 kilometers) per hour 2 miles (3.2 kilometers) from ground zero. The blast wave and wind probably would kill the majority of people within 3 miles (4.8 kilometers) of ground zero and some of the people between 3 and 6 miles (4.8 and 9.6 kilometers) from ground zero. In addition, many other people within 6 miles of ground zero would be injured.

Thermal radiation consists of ultraviolet, visible, and infrared radiation given off by the fireball. The ultraviolet radiation is rapidly absorbed by particles in the air, and so it does little harm. However, the visible and infrared radiation can cause eye injuries as well as skin burns called flash burns. Between 20 and 30 per cent of the deaths at Hiroshima and Nagasaki resulted from flash burns. Thermal radiation also can ignite such highly flammable materials as newspapers and dry leaves. The burning of these materials can lead to large fires. Some scientists theorize that, in a nuclear war, the smoke from such fires would absorb enough sunlight to lower the temperature of much of the earth's surface for several months or years. These scientists speculate that the lowered temperatures would result in widespread crop failure and famine. This possible effect of nuclear war is known as nuclear winter. However, the effects of thermal radiation can vary considerably, depending on a number of conditions at the time of the explosion. When a light atmospheric haze is present, for example, the effects could be only one-hundredth as strong as they would be if the air were clear.

A person can be shielded from the direct effects of thermal radiation by such solid, nontransparent objects as walls, buildings, trees, and rocks. In addition, light-colored clothing, which reflects heat, can help protect a person from flash burns. However, thermal radiation produced by a 1-megaton explosion can produce second-degree burns (blistering) in exposed human skin up to 11 miles (18 kilometers) from ground zero. The thermal radiation would last only about 10 seconds. Thus the radiation would char, but not completely burn, heavy fabrics and thick pieces of wood or plastic.

Initial nuclear radiation is given off within the first minute after the explosion. It consists of neutrons and gamma rays. The neutrons and some of the gamma rays are emitted from the fireball almost instantaneously. The rest of the gamma rays are given off by a huge mushroom-shaped cloud of radioactive material that is formed by the explosion. Nuclear radiation can cause the swelling and destruction of human cells and prevent normal cell replacement. Large doses of radiation can cause death. For more information about how radiation affects the human body.

The amount of harm a person would suffer from initial nuclear radiation depends in part on the person's location in relation to ground zero. Initial radiation decreases rapidly in strength as it moves away from ground zero. In all nuclear explosions, for example, the initial radiation at about 1/3 to 2/3 mile (0.5 to 1 kilometer) from ground zero is only about one-tenth to one-hundredth as strong as the radiation at ground zero.

Residual nuclear radiation is given off later than one minute after the explosion. Residual radiation created by fission consists of gamma rays and beta particles (electrons). Residual radiation produced by fusion is made up primarily of neutrons. It strikes particles of rock, soil, water, and other materials that make up the mushroom-shaped cloud. As a result, these particles become radioactive. When the particles fall back to earth, they are known as fallout. The closer an explosion occurs to the earth's surface, the more fallout it produces.

Early fallout consists of heavier particles that reach the ground during the first 24 hours after the explosion. These particles fall mostly downwind from ground zero. Early fallout is highly radioactive and will kill or severely damage living things.

Delayed fallout reaches the ground from 24 hours to a number of years after the explosion. It consists of tiny, often invisible, particles that may fall in small amounts over large areas. Such fallout causes long-term radiation damage to living things.

Strategic and theater nuclear weapons

Nuclear weapons can be divided into two main types, depending on the military role for which they are designed. These types are (1) strategic nuclear weapons and (2) theater nuclear weapons.

Strategic nuclear weapons are designed primarily to launch an attack from great distances on targets in an enemy's homeland. These weapons include bombs and missiles delivered by long-range bomber aircraft. They also include missiles that can deliver explosive devices to targets that generally are up to 6,500 miles (10,500 kilometers) from the launch site. Some of these missiles are based on land. Others are based underwater on submarines. Strategic nuclear missiles include intercontinental ballistic missiles (ICBM's), submarine-launched ballistic missiles (SLBM's), and cruise missiles.

Some strategic nuclear missiles have a number of nuclear warheads, each of which carries explosive material to a separate target. These warheads are called Multiple Independently Targetable Reentry Vehicles (MIRV's).

Strategic nuclear weapons can destroy or disable an enemy's strategic nuclear weapons. They also can disrupt an enemy's economy or social organization.

Theater nuclear weapons are designed for use within a military theater, a large geographic area in which conventional warfare is taking place. Smaller or shorter-range theater nuclear weapons are also called tactical nuclear weapons. Theater nuclear weapons can be used to attack conventional forces during a battle or military campaign, or to attack the enemy's theater nuclear weapons. Theater nuclear weapons include medium-range ballistic and cruise missiles. They also include short -range guided missiles and unguided rockets; artillery shells; nuclear mines; and torpedoes.

Nuclear weapons in military planning

The first nuclear weapons were built just as the United States and the Soviet Union were becoming the world's leading military powers. Later, tensions between the two countries greatly contributed to the growth of each nation's arsenal (supply) of nuclear weapons.

The United States. Since the mid-1930's, some U.S. military planners have considered airpower a means of ending a war quickly. Before World War II, they thought that a war could be shortened by using bombers to strike a quick, crushing blow against an aggressor's homeland. During World War II, this airpower theory led the United States to drop many conventional bombs on Germany and Japan. However, Germany surrendered only after its army was defeated by Allied ground troops. Japan surrendered after two nuclear bombs were dropped on Hiroshima and Nagasaki.

United States supporters of the airpower theory thought that the successful use of nuclear bombs against Japan confirmed the theory. As a result--and because nuclear weapons are far cheaper to build and maintain than conventional forces--nuclear weapons became the main source of U.S. strategic military power.

In the mid-1950's, the United States adopted the policy of massive retaliation. This policy stated that if Soviet forces struck any area vital to the interests of the United States and its allies, the United States might respond with a major nuclear strike against the Soviet Union.

In the early 1960's, the policy of massive retaliation was replaced by that of flexible response. According to this policy, the U.S. response to enemy aggression would begin with the use of conventional forces. Then, if these forces failed to defeat the aggressor, the United States would use theater nuclear weapons. The United States would attack with strategic nuclear weapons only if theater weapons failed to defeat the aggressor. In 1990, the United States announced it intended to amend its policy to one in which any kind of nuclear weapon would be used only as a last resort.

The Soviet Union. Beginning in the 1930's, Soviet military planners based their military strategy on the deep battle theory. Unlike U.S. planners, who have emphasized the use of airpower as a response to attack, Soviet planners long stressed the use of all available weapons in an early and overwhelming offensive against enemy forces. Soviet planners preferred that such an attack be a surprise. Most experts believed such a strike could include nuclear weapons. The Soviet strategic nuclear arsenal had long been based mainly on large land-based missiles. A portion of them could possibly cripple the U.S. land-based missile and bomber forces in a first strike (initial nuclear attack). After the Soviet Union dissolved in late 1991, most concern about the possible use of Soviet nuclear weapons shifted from their use under a military plan to uncontrolled use by rival political groups or terrorists.

Control of nuclear weapons

Since 1945, the combined explosive power of all the world's nuclear weapons has increased enormously. Because of the great dangers associated with nuclear weapons, many attempts have been made to control them. The chief approaches to control have been strategies of deterrence and the placing of limits on the testing, numbers, and proliferation of nuclear weapons.

Deterrence refers to preventing the countries that have nuclear weapons from using them. Theories of deterrence may be offense-based or defense-based.

Offense-based deterrence theory holds that the possession of a strong nuclear force by each of two opposing nations will best prevent nuclear war between the two countries. Each force must be so large that, following a first strike, enough of the defender's weapons would be left over to deliver a devastating blow to the aggressor's homeland. The theory relies on a potential aggressor's believing that if it launched a nuclear attack, it would suffer unacceptable destruction in return.

Some experts interpret the theory to require that neither nation have a major defense against a nuclear strike. In 1972, the United States and the Soviet Union concluded a treaty that limited each country's deployment of defensive missiles. These missiles, known as antiballistic missiles or ABM's, destroy incoming nuclear missiles before they reach their targets.

Defense-based deterrence theory holds that only a defense against a first strike will reliably prevent a nuclear attack. This theory rests on the belief that an aggressor will not attack if it is not sure it can destroy the victim's ability to launch a nuclear counterattack. No country has a defense that would create such uncertainty. In 1983, the United States began focusing research efforts on a program known as the Strategic Defense Initiative (SDI). However, the United States ended SDI in 1993.

Limiting testing. Nations have sought to limit the testing of nuclear weapons to protect people and the environment from nuclear radiation and to slow the development of nuclear weapons. In 1963, the Soviet Union, the United Kingdom, and the United States negotiated the first--and chief--test limitation treaty, the Limited Test Ban Treaty. The treaty's signers agreed not to test nuclear weapons in the atmosphere, in outer space, or underwater. Only underground testing was not banned.

In 1974, the United States and the Soviet Union agreed not to test explosive devices with yields above 150 kilotons. A kiloton is the amount of energy released by 1,000 short tons (907 metric tons) of TNT. The treaty that contains the agreement, called the Threshold Test Ban Treaty, was not ratified by either country. But both nations agreed to follow the treaty's guidelines.

In 1996, the United Nations approved the Comprehensive Nuclear Test Ban Treaty, which would end all testing of nuclear weapons--even underground testing. To go into effect, the treaty must be ratified by all countries that have nuclear reactors (devices for producing nuclear energy).

Nonproliferation refers to efforts to prevent the spread of nuclear weapons to nations that do not have them. The main treaty designed to halt nuclear proliferation is the Treaty on the Non-Proliferation of Nuclear Weapons. It was approved by the United Nations in 1968 and has since been ratified by about 180 countries.

Limiting numbers. Attempts to limit the number of U.S. and Soviet nuclear weapons began about 1970. Limits were first established in the Strategic Arms Limitation Talks (SALT). These talks, which aimed at setting limits at then-existing levels for some weapons and at higher levels for others, resulted in the SALT I and SALT II agreements of 1972 and 1979. SALT I was ratified by both nations. However, the U.S. Senate refused to ratify SALT II after the Soviet invasion of Afghanistan in 1979.

In 1982, the United States and the Soviet Union began the Strategic Arms Reduction Talks (START). These talks aimed at reducing the number of strategic nuclear weapons held by each nation. In July 1991, U.S. President George Bush and Soviet President Mikhail Gorbachev signed the Strategic Arms Reduction Treaty (also called START) to reduce the nuclear weapons and delivery systems of each country by about a third.

In 1987, the two countries signed the Intermediate-Range Nuclear Forces (INF) Treaty. This treaty called for the elimination of all U.S. and Soviet ground-launched nuclear missiles with ranges of 500 to 5,500 kilometers (310 to 3,420 miles). It took effect on June 1, 1988.

Political reform. Perhaps the key obstacle to controlling nuclear weapons was the lack of trust between the United States and the Soviet Union and their respective allies. These relations began to improve significantly in the late 1980's as Soviet President Gorbachev's principles of glasnost (openness) and perestroika (restructuring) brought changes to the Soviet political system.

The first effect on nuclear weapons control was the rapid completion of the INF treaty. Soon afterward, Gorbachev also rejected the Soviets' traditional use of conventional military forces to suppress political liberalization in Eastern Europe. In 1989, nearly all the Communist governments there collapsed. This dramatic reform led to major progress to reduce the threat posed by conventional forces in Europe. In November 1990, the United States, the Soviet Union, and 20 other nations signed the Conventional Forces in Europe (CFE) Treaty to reduce and control those forces. These developments set the stage for the signing of the START pact in July 1991. The CFE treaty went into effect in July 1992.

In September 1991, the United States announced that it would immediately take out of service all of its tactical nuclear weapons, except those carried by certain aircraft. The United States would destroy all of its ground-based tactical nuclear weapons and some of those carried by ships and aircraft. The following month, the Soviet Union announced that it would take similar steps.

The Soviet Union itself broke up at the end of 1991. Most of the former republics of the Soviet Union joined a loose association called the Commonwealth of Independent States (C.I.S.). The breakup appeared to end any immediate threat of large-scale nuclear war.

However, the breakup also raised concerns over who would control former Soviet nuclear weapons, possible spread to terrorists or others, and the fate of arms-control agreements signed by the Soviet Union. Four of the former Soviet republics--Belarus, Kazakstan, Russia, and Ukraine--had strategic nuclear arms at the time of the breakup. In May 1992, they and the United States signed an agreement to abide by START. Later that year, under the CFE treaty, they began to reduce their conventional weapons and force levels. Ukraine, Kazakstan, and Belarus also agreed to turn over all strategic weapons to Russia. Finally, C.I.S. members agreed that former Soviet nuclear weapons would be controlled jointly, under the authority of the C.I.S.

In January 1993, U.S. President George Bush and Russian President Boris Yeltsin signed START II, a new arms-reduction treaty that supplements START, now called START I. While START I cuts U.S. and former Soviet strategic weapons from 23,500 to 15,400, START II cuts the number to between 6,000 and 7,000. START II also eliminates land-based MIRV's. In 1994, Ukraine became the last of the former Soviet republics with nuclear weapons to ratify START I. By the end of 1996, Belarus, Kazakstan, and Ukraine had turned over all their nuclear weapons to Russia.

History

The beginnings. Scientists gained an understanding of the basic structure of the atom during the late 1800's and early 1900's. In 1938, researchers discovered that splitting the nucleus of a uranium atom released much energy.

World War II. By early 1939, only months before the start of World War II, physicists in the United States had become aware of the potential military applications of nuclear energy. They became concerned Nazi Germany might develop a nuclear weapon. In August 1939, the German-born physicist Albert Einstein helped alert U.S. President Franklin D. Roosevelt to the potential military applications of nuclear fission. World War II began on Sept. 1, 1939. The United States entered the war in December 1941. In 1942, the U.S. government set up the Manhattan Project to design and build a fission bomb.

On July 16, 1945, Manhattan Project scientists led by the American physicist J. Robert Oppenheimer exploded the first experimental nuclear device. The device, set off at the Trinity test site near Alamogordo, New Mexico, was a 22-kiloton implosion-type fission device. The test convinced U.S. leaders that fission weapons could be built.

The first nuclear weapon used by the United States against Japan was a gun-type fission bomb. It had a yield of about 13 kilotons. The bomb was dropped from a B-29 aircraft on the city of Hiroshima on Aug. 6, 1945. Three days later, another B-29 dropped a 22-kiloton implosion-type fission bomb on Nagasaki, Japan. These bombs largely destroyed both cities, but the number of deaths differed greatly. The smaller bomb killed from 70,000 to 100,000 people in Hiroshima, which has a flat terrain. The larger bomb killed about 40,000 in Nagasaki, which has a hilly terrain. Other people in both cities died later of injuries and radiation. On Aug. 14, 1945, Japan agreed to surrender, ending World War II.

The Cold War. By the late 1940's, tension between the Soviet Union and the United States led to a bitter struggle known as the Cold War. During the Cold War, many nuclear weapons were developed.

In 1949, the Soviet Union tested its first fission device in the midst of rising tension. In 1952, during the Korean War, the United States exploded the first experimental thermonuclear device. The Soviet Union set off its first weapon-grade thermonuclear device in 1955. In the mid-1950's, the Soviets built the first submarines equipped with nuclear missiles. In 1957, they test-launched the first land-based intercontinental ballistic missile (ICBM). The first U.S. ICBM became operational in 1959. Also in 1959, the United States commissioned its first submarine equipped with SLBM's. The first MIRV's were acquired in the 1970's, first by the United States and then by the Soviet Union.

Recent developments. Political developments in Eastern Europe and the Soviet Union from 1989 to 1991 ended the Cold War. Concern in Europe has shifted from fear of massive conventional attack to ensuring political--and therefore military--stability. Military analysts expect that reduced nuclear arsenals, if properly controlled, will continue to help prevent political tensions from developing into a major war.

Contributor: George W. S. Kuhn, J.D., Research Fellow, Logistics Management Institute; Former United States Army Officer.

Jeffrey G. Barlow, Ph.D., Historian, Contemporary History Branch, Naval Historical Center.

Additional resources

Cantelon, Philip L., and others, eds. The American Atom. 2nd ed. Univ. of Pa. Pr., 1991. History of nuclear policies.

Hafemeister, David, ed. Physics and Nuclear Arms Today. Am. Inst. of Physics, 1991.

Jagger, John. The Nuclear Lion: What Every Citizen Should Know About Nuclear Power and Nuclear War. Plenum, 1991.

Rotblat, Joseph, and others, eds. A Nuclear-Weapon-Free World. Westview, 1993.