A History of Nuclear Weapons

DISARMAMENT

5 min read

Nuclear Weapons

The term nuclear weapons refers to weapons that exploit the energy released by explosive nuclear fission or fusion reactions. A nuclear weapon consists of a nuclear warhead and a delivery system, normally a long-range bomber or missile.

There are two principal types: the fission nuclear bomb (or atomic bomb, A-bomb) and the more powerful fusion nuclear bomb (or thermonuclear bomb, hydrogen bomb, H-bomb). Without going into technical details, the former derives its energy from the chain fission—the splitting—of the nuclei of uranium or plutonium atoms. The latter derives most of its energy from the fusion—the joining—of hydrogen nuclei, triggered by the extremely high temperatures produced by the explosion of a fission bomb, which serves as the initiator.

A third type is the so-called neutron bomb (or N-bomb). Its energy is likewise produced by fusion reactions, but the weapon is designed to limit the release of mechanical and thermal energy—blast and heat—while maximizing the emission of radiation, thereby producing particularly lethal immediate effects on living organisms.

The missiles used to deliver nuclear weapons to their targets are generally divided into ballistic missiles and cruise missiles. Ballistic missiles are launched into the atmosphere and follow a parabolic trajectory, part of which may extend beyond the atmosphere. Cruise missiles are more similar in shape to aircraft and are equipped with guidance systems that allow them to control their trajectory along a predetermined route.

Ballistic missiles are further divided into strategic and tactical missiles. Strategic missiles include intercontinental ballistic missiles (ICBMs), with ranges of up to 15,000 kilometers, and intermediate-range ballistic missiles (IRBMs), with ranges of up to 5,000 kilometers. Tactical missiles include short-range missiles, with ranges of up to 1,000 kilometers.

The Effects of a Nuclear Explosion

The explosion of a nuclear weapon produces four principal destructive effects: blast, thermal radiation (heat), initial nuclear radiation, and residual nuclear radiation. The proportion of energy released in each of these forms varies according to the weapon's yield, the location of the explosion, and the characteristics of the surrounding environment.

The first three effects occur only during the period immediately following the detonation. Residual radiation, by contrast, persists for a much longer period. It is responsible for the phenomenon known as radioactive fallout: the return to the ground of the radioactive cloud formed by material that has been vaporized, lifted into the atmosphere, and rendered radioactive by the explosion.

The term global radioactive fallout refers to the lighter material that is carried into the stratosphere and transported by winds around the planet, eventually settling on the Earth's surface after weeks, months, or even years. Local radioactive fallout, which produces more immediate and concentrated contamination, consists of heavier material falling back to the ground around the site of the explosion, over an area whose extent depends largely on atmospheric conditions.

Fallout is particularly severe when a nuclear weapon is detonated at or near the Earth's surface. In such circumstances, the ground and other material beneath the explosion are incorporated into the radioactive cloud in much greater quantities.

Nuclear radiation produces both immediate and long-term effects on living organisms. Depending on the dose, it can kill cells or alter their functions, with potentially fatal or otherwise harmful consequences for the organism. It can also increase the incidence of genetic mutations, cancer, and other adverse conditions.

From Nuclear Physics to Nuclear Weapons

The first artificial nuclear fission of uranium was achieved by the Italian physicist Enrico Fermi and his collaborators during their experiments in 1934, although they did not recognize the phenomenon for what it was. In 1938, the German chemists Otto Hahn and Fritz Strassmann experimentally identified and conclusively demonstrated nuclear fission.

The significance of the discovery soon became clear. It opened the possibility of exploiting the enormous energy released by nuclear reactions not only for civilian purposes, but also for military ones.

On August 2, 1939, Albert Einstein wrote to United States President Franklin D. Roosevelt, warning him of the possibility—suggested by the progress of research by Joliot, Fermi, and Szilard—that a nuclear chain reaction could be produced in a large mass of uranium and that this could make possible a new type of bomb.

Einstein therefore urged the United States government to accelerate experimental work and provide the necessary funding. He also warned that Germany had halted the export of uranium from the Czechoslovak mines and that researchers in Berlin were repeating some of the work carried out in the United States by Fermi and Szilard.

In 1941, President Roosevelt established a committee to coordinate what became known as the Manhattan Project, whose purpose was the development of a nuclear weapon.

After Roosevelt's death in April 1945, his successor, President Harry Truman, established an Interim Committee to advise him on the possible use of the weapon. It was assisted by a Scientific Panel that included, among others, the physicists Enrico Fermi and J. Robert Oppenheimer.

In May 1945, at a meeting in Los Alamos, potential targets were selected according to three criteria. They had to be:

important and located within a large urban area, more than three miles in diameter;
sufficiently vulnerable to an atomic explosion to be effectively damaged; and
unlikely to be attacked by conventional means before August.

The first criterion is particularly significant because it reveals that the intended targets were not exclusively military. Civilian populations were necessarily part of the equation.

This intention is further clarified by what the minutes of the meeting called the “psychological factors in target selection.” The attack was expected to produce the maximum possible psychological effect on Japan and to be sufficiently spectacular to demonstrate internationally the significance of the new weapon.

Kyoto, the former Japanese capital, with a population of approximately one million, and Hiroshima were initially recommended as targets on the basis of these criteria.

On June 1, 1945, after consulting the Scientific Panel, the Interim Committee recommended that the weapon be used against Japan as soon as possible and without prior warning.

On July 16, in the New Mexico desert, the first nuclear weapon was detonated in the secret Trinity test.

The Decision to Use the Bomb

The development of the bomb did not, however, produce unanimous support for its use.

On July 17, seventy scientists who had participated in the development of the atomic bomb, led by Leo Szilard, sent President Truman a petition. They urged the government to issue a public warning about the effects of the new weapon and to use it only if Japan refused to surrender.

At the same time, they argued that any decision to use the weapon should be subjected to a moral and political assessment of its consequences. Among the possibilities they explicitly contemplated was the beginning of an era of devastation on a scale that could not yet be imagined.

The warning was rejected.

On August 6, 1945, a uranium bomb, code-named Little Boy, was dropped on Hiroshima. Approximately 140,000 people had died there by the end of 1945, either immediately or as a consequence of the bombing. The number would rise to approximately 200,000 over the following five years.

Three days later, on August 9, a plutonium bomb, Fat Man, was dropped on Nagasaki, which had replaced other targets previously designated. Approximately 70,000 people died there by the end of 1945, with the number reaching approximately 140,000 over the following five years.

On August 15, Japan announced its unconditional surrender.

The Legal Question

The legality of the attacks was questioned immediately.

Truman stated that Hiroshima had been selected because it was, in his words, a “military base,” and that the decision had therefore been made in order to avoid, as far as possible, the killing of civilians.

He also argued that, having developed this new weapon, the United States had used it against a country that had attacked Pearl Harbor without warning, and that the bombings were intended to bring the war to an earlier end and thereby save the lives of thousands of young American soldiers.

The first of these arguments has not survived subsequent historical scrutiny. Declassified documents concerning the work of the Interim Committee, including the target-selection criteria described above, contradict the characterization of Hiroshima as simply a military target and demonstrate that the potential effects on the civilian population were part of the decision-making process.

The other arguments are political—or, at most, moral—rather than legal.