"Webster's Ninth New Collegiate Dictionary" defines the term "chemical warfare," first used in 1917, as "tactical warfare using incendiary mixtures, smokes, or irritant, burning, poisonous, or asphyxiating gases." A working definition of a chemical agent is "a chemical which is intended for use in military operations to kill, seriously injure, or incapacitate man because of its physiological effects. Excluded from consideration are riot control agents, chemical herbicides and smoke and flame materials." Chemical agents were usually divided into five categories: nerve agents, vesicants, choking agents, blood agents, and incapacitates. This chapter focuses primarily on the development of chemical and biological weapons and countermeasures to them, thus setting the stage for Chapter 3, Historical Aspects of Medical Defense Against Chemical Warfare, which concentrates on medical aspects of chemical warfare. To avoid excessive duplication of material, protective equipment of the modern era is illustrated in Chapter 16, Chemical Defense Equipment.
Textbook of Military Medicine: Medical Aspects of Chemical and Biological Warfare, p. 9-86