Chemical weapons use the toxic properties of chemical substances rather than their explosive properties to produce physical or physiological effects on an enemy.
Although instances of what might be styled as chemical weapons date to antiquity, much of the lore of chemical weapons as viewed today has its origins in World War I. During that conflict "gas" (actually an aerosol or vapor) was used effectively on numerous occasions by both sides to alter the outcome of battles. A significant number of battlefield casualties were sustained. The Geneva Protocol, prohibiting use of chemical weapons in warfare, was signed in 1925. Several nations, the United States included, signed with a reservation forswearing only the first use of the weapons and reserved the right to retaliate in kind if chemical weapons were used against them (the United States did not ratify the Protocol until 1975). Chemical weapons were employed in the intervening period by Italy (in Ethiopia) and Japan (in Manchuria and China). Both nations were signatories to the Geneva Convention. Chemical weapons were never deliberately employed by the Allies or the Axis during World War II, despite the accumulation of enormous stockpiles by both
sides. Instances of employment of chemical weapons in local wars since then are
arguable, although they were definitely used in the Iran-Iraq conflict of 1982-87.
Development of chemical weapons in World War I was predominantly the adaptation of a chemical "fill" to a standard munition. The chemicals were commercial chemicals or variants. Their properties were, for the most part, well known. The Germans simply opened canisters of chlorine and let the prevailing winds do the dissemination. Shortly thereafter the French put phosgene in a projectile and this method became the principal means of delivery. In July 1917, the Germans employed mustard shells for the first time and simultaneously attempted to use a solid particulate emetic, diphenyl chloroarsine, as a mask breaker. Mustard, an insidious material, penetrates leather and fabrics and inflicts painful burns on the skin.
These two themes, along with significant increases in toxicity, represent a large segment of the research and development of chemical weapons that nations have pursued over the years. There is first the concept of agents that attack the body through the skin, preferably also through clothing, and more preferably through protective clothing. Along with that concept is the idea of penetrating or "breaking" the protective mask so that it no longer offers protection for the respiratory system. Increasing the toxicity of the chemical agent used would theoretically lower the amounts required to produce a battlefield effect.
Unless this increase is significant, however, it can be masked by the inefficiencies of disseminating the agent. Consequently, later development has focused on the methods for delivering the agent efficiently to the target.
The chemicals employed before World War II can be styled as the "classic" chemical weapons. They are relatively simple substances, most of which were either common industrial chemicals or their derivatives. An example is phosgene, a choking
agent (irritates the eyes and respiratory tract). Phosgene is important in industry as a chlorinating material. A second example is hydrogen cyanide, a so-called blood agent (prevents transfer of oxygen to the tissues), now used worldwide in the manufacture of acrylic polymers. The classic chemical agents would be only marginally useful in modern warfare and generally only against an unsophisticated opponent. Moreover, large quantities would be required to produce militarily significant effects, thus complicating logistics.
Blister agents or vesicants are an exception to the limited utility of classic agents. Although these materials have a relatively low lethality, they are effective casualty agents that inflict painful burns and blisters requiring medical attention even at low doses. The classic mustard is the most popular among proliferant nations since it is relatively easy to make. Mustard is generally referred to as the "king" of agents because of its ease of production, low cost, predictable properties, persistence, and ability to cause resource-devouring casualties rather than fatalities. Its insidious nature is both an advantage and a disadvantage. Mustard on the skin causes no immediate sensation and symptoms normally do not appear until several hours after exposure. At incapacitating levels this may be as long as 12 hours. (Contrary to the normal expectation, horrible fatalities occurred in the Iran-Iraq War because Iranian soldiers, feeling no effects, continued to wear mustard soaked clothing and inhale its fumes.)
To produce immediate effects, an arsenical vesicant known as lewisite was developed in the United States. Much of the former Soviet Union vesicant stocks were
mixtures of lewisite and sulfur mustard. Between the world wars the development of chemical weapons included adaptation to aircraft delivery (bombs) and exploitation of lewisite, since the more potent mustard was, from a battlefield perspective, slow in producing casualties. Independent experiments in several countries led them to consider/adopt mixtures of mustard and lewisite as fills for chemical munitions.
The Italians, Hungarians, Japanese, French, English, Russians, and Americans, as
well as the Germans, all perfected mustard, phosgene, and similar agents during World War II. Although never used in the conflict, these nations amassed such huge quantities of chemical munitions that their disposal presented a practical problem, one that would be virtually insurmountable in today's more environmentally conscious world. In those more naive times, however, the munitions simply found their way to the bottoms of almost all the world's oceans in the holds of expendable ships.
Nerve gases are liquids, not gases, which block an enzyme (acetylcholinesterase)
that is necessary for functions of the central nervous system. Nerve agents are generally divided rather arbitrarily into G- and V-agents, although there are numerous structural variants that are potent cholinesterase inhibitors. Nerve agents known to date to have been produced for chemical warfare purposes are all organo-phosphorus compounds and are liquids at room temperature. Similar in action to many pesticides, they are lethal in much lower quantities than classic agents. The nerve gases are effective when inhaled or when absorbed by the skin (percutaneous), or both, although there are differences in effectiveness. In general, the lower the material's volatility (and hence its inhalation threat), the greater its percutaneous toxicity.
Nerve gases, or anticholinesterase agents, were discovered by the Germans in the
1930's and developed during World War II. In 1936 during studies of possible pesticides, the German chemist Gerhard Schrader discovered what he called "tabun" or
GA. Two years later Schrader discovered the even more toxic "sarin" or GB. These
compounds are orders of magnitude more toxic than those used in World War I and
thus represent the significant toxicity increase that changed the concept of employment. Fortunately for the Allies, the Germans never exploited their technological advantage, although they did produce a large number of tabun-filled munitions.
After World War II the victors took an interest in exploiting the potential of the remarkably potent "nerve" agents. The British, in particular, had captured small stocks of sarin (GB) and set about investigating its potential. The Soviets removed the Germans' GB production plant to the Soviet Union. GB turned out to be perhaps the best of the respiratory agents, being volatile as well as exceedingly toxic. The United States designed a cluster bomb to exploit the characteristics of GB and followed this with a litany of adaptations of munitions. Artillery rockets were produced as were bombs, projectiles, and spray tanks. Many of these used the basic design of high-explosive weapons and simply changed the fill to GB. In the instance of the spray tank, it was necessary to use a polymeric thickening material so that the liquid would form large droplets and not evaporate before it reached the ground.
The French, British, and Canadians all built small-scale facilities to produce the GB for testing. The United States, however, entered into full-scale production of GB, as did the Russians just a little later. The Russians also produced soman (GD), an agent the U.S. developers had decided to forswear because of its properties of being refractory to treatment above a single lethal dose.
In the late 1950's, UK scientists discovered another category of nerve agents, the V-agents. These were particularly interesting in that most of them were very effective percutaneously and represented an effective way to circumvent the ubiquitous gas mask. The United States and the UK pursued a form of V-agent called VX, although they produced it by entirely different processes. The Russians exploited another structural analog that proved more adaptable to their industrial processes.
The 1960's saw continued development in nonlethal agents, or riot control agents, first used in World War I. These materials, most notably CS, are strong irritants of the mucous membranes with very high safety ratios. The letters "CS" are code letters for a solid powder classified as a riot-control agent (O-chlorobenzylmalonitrile). This compound is a highly effective irritant of the mucous membranes with an
exceedingly high safety ratio (~63,000). The purpose of CS and similar materials is temporary incapacitation without permanent harm. CS was developed and first used by the UK. It was quickly adopted and used extensively by the United States and since has been produced and employed by many nations. CS is a solid at room temperature and presents a problem for effective dissemination in useful particle sizes. Particulate CS, like most solids, tends to develop an electrostatic charge which causes the particles to agglomerate into larger particles. Much development effort during the 1960's was spent on finding effective dissemination techniques.
The work on particulate CS could be extrapolated to another type of chemical agent that was of extreme interest in the 1960's: incapacitating agents. These were initially seen by some as a panacea to make warfare safe and humane. Thousands of potential compounds were screened, obtained from government sources in the United States and from commercial pharmaceutical companies around the world. Although there were several promising materials, primarily mental incapacitants, only BZ was ever standardized. The problem of incapacitants, or incapacitating agents, is complex. The use of incapacitants in warfare is considered to be prohibited by the Chemical Weapons Convention even though only a single agent, BZ (3-quinuclidinyl benzilate), and its immediate precursors are included as listed compounds (Schedule 2) in that Treaty. In retrospect, while BZ was the only incapacitating agent formally accepted (i.e., type classified) by the United States, it was a poor choice and is now obsolete. It remained in U.S. stocks for only a short period of time. The substance is a mental rather than a physical incapacitant with long-onset time and unpredictable symptoms. The victim becomes confused and is likely to be incapable of acting decisively. The confusion, however, may not be readily apparent. The duration of action is long, about 48 hours, making prisoner management difficult. There are, moreover, hundreds of compounds more potent, faster acting, and with shorter duration of effect.
Mental incapacitants are predominantly glycolates, whereas some of the more potent candidates for physical incapacitants have come from research on improved anesthetics. Indeed, almost all potential incapacitants are byproducts of the pharmaceutical industry and have legitimate pharmaceutical uses. The defining technologies for such incapacitating weapons, then, are the production of a physiologically effective compound in greater than practical pharmaceutical quantities and incorporation of the material in weapons. It is probable that the physical state of an incapacitant will be a particulate solid and that
the practical route for effective use is by inhalation.
Binary chemical weapons use toxic chemicals produced by mixing two compounds immediately before or during use. Binary weapons do not necessarily employ new toxic chemicals. In U.S. parlance, relatively innocuous precursors were stored separately and reacted to form the toxic chemical agent en route to the target. In principle, the binary concept could also be used to produce highly lethal but unstable compounds or mixtures of compounds unsuitable for long-term storage. The U.S. type classified and produced a GB (sarin) binary nerve agent weapon, the M687 projectile (a 155-mm artillery shell), and was in the late stages of development of two other binary weapons when its offensive CW program was terminated. The Russians have been publicly accused by dissidents within their own agencies of developing new binary agents, and the Iraqis are known to have constructed binary bombs and missile warheads, albeit with crude manual mixing of the reactants.
Other possibilities for chemical agents include toxins and allergens which also
have been, at times, considered biological agents. Although not living organisms themselves, these materials are usually products of living organisms with complex molecular structures. A wide variety of toxins with an equally broad spectrum of chemical, physical, and physiological properties exists.
Until the recent attempts at terrorism by the Japanese cult Aum Shinrikyo, virtually all uses of chemical weapons have been as tactical weapons by nations. These have ranged from attempts to break the stalemate in World War I to the recent use by Iraq to blunt Iranian human wave attacks in the Iran-Iraq War (1982-87). Chemical weapons were not employed by the major protagonists in World War II. Between World Wars I and II, two signatories of the Geneva Protocol (Italy and Japan) employed chemical weapons. Typically, nations have employed them against unprotected targets and not against an equally well-armed nation; chemical weapons are therefore arguably an example of mutual deterrence. Although there have been charges of chemical weapon use in virtually every conflict in recent decades, most have not been substantiated by clinical or physical evidence.