Chemical Warfare and Its Uses Chemical warfare is the use of natural and man-made toxic substances to incapacitate or kill an enemy. There are many different types of agents used in chemical warfare, some of which are mustard gases, nerve gases, psychotomimetic agents, tear gases, hydrogen cyanide, and arsines. All of which are very poisonous and lethal when exposed to humans in large amounts. Until the 20th century such warfare was primarily limited to starting fires, poisoning wells, distributing smallpox-infected articles, and using smoke to confuse the enemy. Today however, it is used as lethal comba