The employment of a chemical agent directly for military purposes, i.e., to cause casualties by irritating, burning, asphyxiation, or poisoning; to contaminate the ground; to screen action by smoke; or to cause incendiary damage. Includes use of all forms of toxic or irritating gases, including nerve gases, smoke-inducing agents, flammable gels such as napalm, and incendiary materials such as magnesium and thermite. Biological warfare involves the use of bacteria and other infective agents against enemy forces or populations.