Agent Orange, so-called because of the orange stripe on the drums in which it was stored, contained dioxin, one of the most toxic chemicals known. An estimated 80 million litres of the defoliant, containing 386kg of dioxin, were sprayed on Vietnam. One millionth of a gram per kilo of body weight is enough to induce cancers, birth defects and other diseases when exposure persists over a long period - as the US veterans discovered in the years after the war.
Cancers, birth defects and other diseases struck the returning veterans in unexpected numbers. Those who had had contact with the chemical sued the manufacturers and in 1984 won what was then the largest ever settlement of $180m against seven of the world's biggest chemical companies, including Dow and Monsanto. But more than 20 years on, while the Americans who did the spraying have been compensated, the Vietnamese who had the toxic chemical sprayed on them are still waiting for redress.
Last year, Vietnamese veterans sued the same US chemical companies claiming that they knew Agent Orange contained a poison - dioxin - and their action in supplying it to the US government breached international law and constituted a war crime. They lost in the first round but they are pinning their hopes on an appeal, due to be heard in Brooklyn, New York, this month.