The U.S. military used aircraft to spray Agent Orange in order to deprive enemy Viet Cong soldiers of thick jungle that they used for cover, whether for snipers along riverbanks or for supply roads secretly carved through the undergrowth. Other uses of Agent Orange included destroying crops that the Viet Cong relied on for food.
The Vietnam War wasn't the first use of herbicides in war -- for example, the British deployed herbicides against Malaysian rebels in the 1950s -- but it was by far the most ambitious. Over the course of more than 6,000 missions, 10 percent of Vietnam was sprayed with Agent Orange [source: BBC News]. Agent Orange was sprayed secretly in Cambodia and in Laos to undermine the Ho Chi Minh Trail, a key supply route for the Viet Cong.
When deployed, Agent Orange kills vegetation of all types, destroying roots as well. Leaves die and fall off, transforming a thick forest into a mass of barren trees. Once green areas turn black. A sharp, unpleasant odor fills the air [source: Glaberson].
In his pioneering research, Galston worked with the growth regulator triiodobenzoic acid, which in smaller doses spurs plants to flower more quickly but in larger doses causes leaves to fall off. The same principle is applied to Agent Orange. Plants subjected to Agent Orange die because the substance contains an excess of growth regulators that cause plant tissue to grow too rapidly and for plants to dry out [source: Buckingham].
Besides the effects previously described, Agent Orange had some other consequences for Vietnam's ecology. The topsoil, so vital to supporting thick jungle growth, disappeared after the monsoon rains without plant life to anchor it [source: Aschwanden]. Invasive species of grasses appeared, hindering the regrowth of the environment's native plant life. The agricultural industry, a major part of Vietnam's economy and its people's livelihood, was ravaged. And into the soil seeped large quantities of dioxin, a deadly substance that we'll look at on the next page.