During the Vietnam War, the United States military used chemical agents in its fight against Ho Chi Minh's Army of North Vietnam and the Viet Cong. The most important of those chemical weapons were the incendiary napalm and the defoliant Agent Orange.
Napalm is a gel, which in its original form contained naphthenic and palmitic acid plus petroleum as fuel. The modern version, Napalm B, contains plastic polystyrene, hydrocarbon benzene, and gasoline. It burns at temperatures of 800 to 1,200 °C (1,500 - 2,200 °F).
When napalm falls on people, the gel sticks to their skin, hair, and clothing, causing unimaginable pain, severe burns, unconsciousness, asphyxiation, and often death. Even those who do not get hit directly with napalm can die from its effects, since it burns at such high temperatures that it can create firestorms that use up much of the oxygen in the air. Bystanders also can suffer heat stroke, smoke exposure, and carbon monoxide poisoning.
The US first used napalm during World War II in both the European and Pacific theaters, and also deployed it during the Korean War. However, those instances are dwarfed by American use of napalm in the Vietnam War, where the US dropped almost 400,000 tons of napalm bombs in the decade between 1963 and 1973. Of the Vietnamese people who were on the receiving end, 60% suffered fifth degree burns, meaning that the burn went down to the bone.
Horrifying as napalm is, its effects at least are time-limited. That is not the case with the other major chemical weapon the US used against Vietnam - Agent Orange.
Agent Orange is a liquid mixture containing the 2,4-D and 2,4,5-T herbicides. The compound is toxic for only about a week before it breaks down, but unfortunately, one of its daughter products is the persistent toxin dioxin. Dioxin lingers in soil, water, and human bodies.
During the Vietnam War, the US sprayed Agent Orange on the jungles and fields of Vietnam, Laos, and Cambodia. The Americans sought to defoliate the trees and bushes, so that enemy soldiers would be exposed. They also wanted to kill off the agricultural crops that fed the Viet Cong (as well as local civilians).
The US spread 43 million liters (11.4 million gallons) of Agent Orange on Vietnam, covering 24% of south Vietnam with the poison. Over 3,000 villages were in the spray zone. In those areas, dioxin leached into people's bodies, their food, and worst of all, the groundwater. In an underground aquifer, the toxin can remain stable for at least 100 years.
As a result, even decades later, the dioxin continues to cause health problems and birth defects for Vietnamese people in the sprayed area. The Vietnamese governments estimates that about 400,000 people have died from Agent Orange poisoning, and about half a million children have been born with birth defects. US and allied veterans who were exposed during the period of heaviest usage and their children may have elevated rates of various cancers, including soft tissue sarcoma, Non-Hodgkin lymphoma, Hodgkin disease, and lymphocytic leukemia.
Victims' groups from Vietnam, Korea, and other places where napalm and Agent Orange were used have sued the primary manufacturers of these chemical weapons, Monsanto and Dow Chemical, on several occasions. In 2006, the companies were ordered to pay $63 million US in damages to South Korean veterans who fought in Vietnam.