Weapons of mass destruction

Weapons of mass destruction (WMD) in principle, refer to weapons of very great hazard and small size relative to their potential harm. The term is somewhat misleading, and the British term weapons of mass effect (WME) clarifies that such an effect may destroy everything in its area of effect, as is the case with a nuclear weapon, but other kinds of weapons several categories of such weapons, such as chemical weapons, biological weapons, and radiological weapons, kill living things but do not destroy inanimate objects.

These four categories, or three if radiological weapons are assumed to be a subset of nuclear weapons, are the most common use. Some politicians and mass media misuse the term for any use of weapons with large-scale effects, such as explosives at the Oklahoma City bombing or the 9-11 Attack. While these were horrible events, large conventional explosives or unusual mechanisms such as crashing airplanes are not within the classic definition.

See counter-proliferation for treaties and other programs to lessen the availability of WMD, and arms control for efforts about their reduction and limitation.

Things that are not WMD

Guided missiles and unmanned aerial vehicles that could have a significant role in delivering WMD payloads are not WMD. Their payloads are WMD.

Be aware there are other classes of weapons for which there are significant concerns about lasting harm (e.g., land mines) or inhumane effect (e.g., blinding weapons and incendiary weapons (see the Convention on Certain Conventional Weapons).

Nuclear weapons

This category covers weapons that produce blast, thermal effects, and both immediate and delayed (i.e., fallout) ionizing radiation by means of nuclear fission or nuclear fusion.

To give an effect of destructiveness with respect to size, while the first nuclear weapons used in World War II weighed approximately 4 tons and had the explosive power of 15-20 kilotons of trinitrotoluene, it is widely assumed that an equally destructive weapon definitely can be no more than 500 kilograms in weight. Skilled designers can reduce that weight significantly; improvised devices by non-national terrorists might be considerably heavier and would need to be a truck or ship bomb.

Five states are "declaratory powers" under the nuclear non-proliferation treaty: China, France, Russia, the United Kingdom, and the United States. Four states, three of which ([[India, [[Israel and [[Pakistan) have never signed the NPT, and North Korea, which is withdrawing, have either demonstrated nuclear weapons, or, in the case of Israel, are assumed to have them by most worldwide intelligence agencies. One state, South Africa, developed nuclear weapons but verifiably disarmed itself of them.

Chemical

Chemical weapons cause temporary or permanent harm by poisoning living things. To be a chemical weapon, the main effect must come through the interaction of a chemical with biological systems. If a given weapon, such as an incendiary (e.g., white phosphorus) can be poisonous but whose major effect is through other means, such as heat, the weapon does not meet generally agreed definitions of chemical weapon.

These are the form of WMD that have been most widely used, most notably in the First World War.

Toxins, which are chemicals produced by living organism, are arguably chemical as well as biological, since the living organisms are not present in the weapon and the effect is to poison system. Nevertheless, the usual convention is to consider them biological weapons, an assumption that will be used in this article.

Biological

Biological weapons are either living organisms, or toxins that are uniquely produced by living organisms. They may be incapacitating or lethal, with a mechanism involving infection of living things, or, in the case of toxins, a mechanism involving things produced by living thing. There has been limited use of them in warfare, primarily by Japan in the Second World War. The Select Agent Program and CDC Bioterrorism Agents-Disease list give examples of high-risk agents.

Since many of the diseases involved occur in nature, such as anthrax, it can be very difficult to distinguish legitimate research or small-scale production (e.g., for vaccines) from weapons preparation.

The known weaponized biological agents generally have the military advantage of a contained effect, in that they generally do not spread from person to person, and only anthrax will remain dangerous for an indefinite time. There have been reports that the Soviets weaponized smallpox, which is contagious or capable of spread between people.

Radiological

Radiological weapons cause effects by ionizing radiation from radioactive isotopes dispersed by conventional explosives or other means that do not involve nuclear fission or fusion at the point of delivery. They are not known to have been used to date, although the world's worst industrial disaster, at Chernobyl, is an extreme example of large-scale contamination by isotopes typical of radiological weapons.

Verification

See National technical means of verification for monitoring nuclear and missile capability. Verification of chemical and biological weapons are considerably more difficult, principally because production facilities for these weapons are very much like facilities used to make legitimate civlian materials.