nuclear warfare

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War involving the use of nuclear weapons. Nuclear-weapons research began in Britain in 1940, but was transferred to the USA after it entered World War II. The research programme, known as the Manhattan Project, was directed by J Robert Oppenheimer. The development of technology that could destroy the Earth by the two major superpowers, the USA and USSR, as well as by Britain, France, and China, has since become a source of contention and heated debate. The worldwide total of nuclear weapons in 1990 was estimated to be about 50,000, and the number of countries possessing nuclear weapons stood officially at five – USA, USSR, UK, France, and China; South Africa developed nuclear weapons in the 1980s but gave them up voluntarily in 1991. India and Pakistan exploded nuclear devices in 1998. Countries suspected of possessing or developing nuclear capability in the 1990s include Israel, North Korea, Iraq, and Iran.

Atom bomb
The original nuclear weapon, the atom bomb, relied on use of a chemical explosion to trigger a chain reaction. The first test explosion was at Alamogordo, New Mexico, on 16 July 1945; the first use in war was by the USA in World War II against Japan on 6 August 1945, over Hiroshima and three days later at Nagasaki.

Use of the atom bomb
By the beginning of 1945 it was clear that Japan could not win the war in the Pacific, although neither its political nor military leaders were prepared to admit defeat. Between March and June US forces took the islands of Iwo Jima and Okinawa against fierce resistance from their Japanese defenders, and carried out huge firebombing raids on major Japanese cities.

On 26 July the Allied Powers issued the Potsdam Proclamation, calling on Japan to surrender unconditionally or face complete destruction. When no response was received, the new US president, Harry S Truman, decided to use the atom bomb against Japan in preference to launching a conventional ground invasion that would have risked many more US lives. Between 100,000 and 240,000 people are thought to have been killed by the bombs in the Japanese cities of Hiroshima and Nagasaki, and the death toll continued to rise in the following decades. The additional threat of defeat and occupation by Soviet forces, following the USSR's declaration of war on Japan on 8 August, persuaded the Japanese government to accept the Allied demand for an unconditional surrender on 14 August.

After the experience of World War II, the threat of nuclear war, the theory of deterrence, and the issue of disarmament became key features of the Cold War 1949–89.

Hydrogen bomb
A much more powerful weapon than the atom bomb, the hydrogen bomb relies on the release of thermonuclear energy by the condensation of hydrogen nuclei to helium nuclei (as happens in the Sun). The first detonation was at Enewetak Atoll in the Pacific Ocean in 1952 by the USA.

Neutron bomb or enhanced radiation weapon (ERW)
The neutron or ERW bomb is a very small hydrogen bomb that has relatively high radiation but relatively low blast, designed to kill (in up to six days) by a brief neutron radiation wave that leaves buildings and weaponry intact.

Nuclear methods of attack
Methods used now include aircraft bombs, missiles (long- or short-range, surface-to-surface, air-to-surface, and surface-to-air), depth charges, and high-powered landmines (‘atomic demolition munitions’) to destroy bridges and roads.

The major subjects of disarmament negotiations are intercontinental ballistic missiles (ICBMs), which have from 1968 been equipped with clusters of warheads (which can be directed to individual targets) and are known as multiple independently targetable re-entry vehicles (MIRVs). The 1980s US-designed MX (Peacekeeper) carries up to ten warheads in each missile. Each missile has a range of about 6,400 km/4,000 mi, and eight MIRVs (each nuclear-armed) capable of hitting eight separate targets within about 240 km/150 mi of the central aiming point.

Nuclear methods of defence
Methods include antiballistic missile (ABM) Earth-based systems with two types of missile, one short-range with high acceleration, and one comparatively long-range for interception above the atmosphere; and the Strategic Defense Initiative (announced by the USA in 1983 to be operative from 2000, but cancelled in 1993; popularly known as the ‘Star Wars’ programme) in which ‘directed energy weapons’ firing laser beams would be mounted on space stations, and by burning holes in incoming missiles would either collapse them or detonate their fuel tanks.

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