War use Gases, Asphyxiating and poisonous 31 Chemical warfare 24 History 23 Vietnam War, 1961-1975 14 Agent Orange 13 Animals 13 more ... Dogs 12 Toxicology 12 Herbicides 9 Veterans 8 World War, 1914-1918 8 Diseases 7 Environmental aspects 7 World War, 1939-1945 5 Working dogs 4 Animal welfare 3 Biological warfare 3 Defoliants 3 Health aspects 3 Terrorism 3 Air defenses 2 Asiatic elephant 2 Biological weapons 2 Decontamination (from gases, chemicals, etc.) 2 First aid in illness and injury 2 Hazardous substances 2 Homing pigeons 2 Human-animal relationships 2 Mascots 2 less ...