The defoliant used in the largest quantity was Agent Orange, a mixture of herbicides now known to have been contaminated with dioxin. About 12 million gallons of Agent Orange were sprayed over Southeast Asia during the American invasion. A prime area of Ranch Hand operations was in the Mekong Delta, where the U.S. Navy patrol boats were vulnerable to attack from the undergrowth at the water's edge. Operation Ranch Hand was concluded May 71 at Bien Hoa AB, RVN.
In 2005, the New Zealand government confirmed that it supplied Agent Orange chemicals to the United States military during the conflict. Since the early 1960s, and up until 1987, it manufactured the 2,4,5T herbicide at a plant in New Plymouth, which was then shipped to U.S. military bases in South East Asia.