Primary Sources: Vietnam War

Operation Ranch Hand was a U.S. military operation during the Vietnam War, lasting from 1962 until 1971. Largely inspired by the British use of 2,4,5-T and 2,4-D (Agent Orange) during the Malayan Emergency in the 1950s, it was part of the overall herbicidal warfare program during the war called "Operation Trail Dust". Ranch Hand involved spraying an estimated 19 million U.S. gallons (72,000 m³) of defoliants and herbicides over rural areas of South Vietnam in an attempt to deprive the Viet Cong of food and vegetation cover. Areas of Laos and Cambodia were also sprayed to a lesser extent. Nearly 20,000 sorties were flown between 1961 and 1971.

The "Ranch Handers" motto was "Only you can prevent a forest" – a take on the popular U.S. Forest Service poster slogan of Smokey Bear. During the ten years of spraying, over 5 million acres (20,000 km²) of forest and 500,000 acres (2,000 km²) of crops were heavily damaged or destroyed. Around 20% of the forests of South Vietnam were sprayed at least once.

The herbicides were sprayed by the U.S. Air Force flying C-123s using the call sign "Hades". The planes were fitted with specially developed spray tanks with a capacity of 1,000 U.S. gallons (4 m³) of herbicides. A plane sprayed a swath of land that was 80 meters wide and 16 kilometers (10 mi) long in about 4½ minutes, at a rate of about 3 U.S. gallons per acre (3 m³/km²). Sorties usually consisted of three to five aircraft flying side by side. 95% of the herbicides and defoliants used in the war were sprayed by the U.S. Air Force as part of Operation Ranch Hand. The remaining 5% were sprayed by the U.S. Chemical Corps, other military branches, and the Republic of Vietnam using hand sprayers, spray trucks, helicopters, and boats, primarily around U.S. military installations.