Operation Ranch Hand was a U.S. Military operation during the Vietnam War, lasting from 1962 until 1971. It was part of the overall herbicidal warfare program during the war called "Operation Trail Dust". Ranch Hand involved spraying an estimated 20 million US gallons of defoliants and herbicides over rural areas of South Vietnam in an attempt to deprive the Viet Cong of vegetation cover and food, in possible violation of the Geneva Conventions.^[1] The United Nations passed a resolution that the use of any kind of biological or chemical weapon to kill plants in time of war is a violation of that protocol. 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 US Forestry poster of Smokey the 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 forest of South Vietnam were sprayed at least once.

The herbicides were sprayed by the US 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 US gallons (4 m³) of herbicides. A plane sprayed a swath of land that was 80 meters wide and 16 km (~10 miles) long in about 4½ minutes at a rate of about 3 US gallons per acre (3 m³/km²).  Sorties usually consisted of 3 - 5 planes flying side by side. 95% of the herbicides and defoliants used in the war were sprayed by the US Air Force as part of Operation Ranch Hand. The remaining 5% were sprayed by the US Chemical Corps and other military branches as well as the RVN by hand sprayers, spray trucks, helicopters and boats primarily around US military installations.

Herbicides

The herbicides used were sprayed up to 50 times the concentration that would have been use in normal agricultural use. The most common herbicide used was Herbicide Orange, more commonly referred to as Agent Orange, a fifty-fifty mixture of two herbicides 2,4-D (2,4-Dichlorophenoxyacetic acid) and 2,4,5-T (2,4,5-Trichlorophenoxyacetic acid). The other most common color coded herbicides used were Agent Blue (cacodylic acid) that was primarily used against food crops and Agent White (picloram) often used when Agent Orange was not available.

The Agents used, known as the rainbow herbicides, their active ingredients and years used were as follow:

• Agent Pink (60% - 40% n-Butyl: isobutyl ester of 2,4,5-T) used in 1961, 1965
• Agent Green(n-Butyl ester 2,4,5-T) unclear when used but believed to be at the same time as Pink
• Agent Purple (50% n-Butyl Ester 2,4-D, 30% n-Butyl ester 2,4,5-T, 20% isobutyl ester 2,4,5-T) used from 1962–1965
• Agent Blue (Cacodylic acid ad sodium Cacodylate) used from 1962 - 1971 (in powder and water solution)
• Agent White (acid weight basis:21.2% tri-isopropanolamine salts of 2,4-D and 5.7% picloram) used from 1966–1971
• Agent Orange (50% n-Butyl ester 2,4-D and 50% -Butyl ester 2,4,5-T) used from 1965–1970

The herbicides were procured by the US military from Dow Chemical Company (all but Blue), Monsanto Company (Orange, Purple and Pink), Hercules Inc. (Orange and Purple), Thompson-Hayward Chemical Company (Orange and Pink), Diamond Alkali/Shamrock Company (Orange, Blue, Purple and Pink), US Rubber Company (Orange), Thompson Chemicals Corporation (Orange and Pink), Agrisect Company (Orange and Purple), Hoffman-Taft Inc (Orange), and the Ansul Chemical Company (Blue).

65% of the herbicides used contained 2,4,5-Trichlorophenoxyacetic acid that was found to have been contaminated with 2,3,7,8-Tetrachlorodibenzodioxin a known human carcinogen.^{[citation needed]} About 12 million gallons of dioxin contaminated herbicides were sprayed over Southeast Asia during American combat operations.

In 2005, the New Zealand government confirmed that Agent Orange chemicals had been supplied from New Zealand to the United States military during the conflict. From 1962 to 1987, 2,4,5T herbicide had been manufactured at an Ivon Watkins-Dow plant in New Plymouth, which was then shipped to U.S. military bases in South East Asia.

Operations

For most of the war 'Operation Ranch Hand' was based out of the Bien Hoa Air Base (1966–1970) for operations in the Mekong Delta region where the U.S. Navy patrol boats were vulnerable to attack from the undergrowth at the water's edge. The storage, mixing, loading, washing and parking ramp was just off the inside taxiway between the Hot Cargo Ramp and the Control Tower. For operations along the central coast and the Ho Chi Minh Trail regions Ranch Hand operated out of the Da Nang Air Base (1964–71). Other bases of operation included Phu Cat AB (1968–1970), Ton San Nhut AB (1962–66), Nha Trang AB (1968–69) Phan Rang AB (1970–72), and Tuy Hoa AB (1971–72).  Other bases were also used as temporary staging areas for Ranch Hand. The Da Nang, Bien Hoa and Phu Cat Air bases are still heavily contaminated with dioxin from the herbicides and have been placed a priority list for containment and clean-up by the Vietnamese government.

The first aerial spraying of herbicides was a test run conducted on August 10, 1961 in a village north of Dak To against foliage. Testing continued over the next year and even though there was doubt in the State Department, the Pentagon and the White House to the efficacy of the herbicides "Operation Ranch Hand" began in early 1962. Individual spray runs had to be approved by President John F. Kennedy until November 1962 when Kennedy gave the authority to approve most spray runs to the Military Assistance Command, Vietnam and the US Ambassador to South Viet Nam. Ranch Hand was given final approval to spray targets in eastern Laos in December 1965.

The issue of whether or not to allow crop destruction was under great debate due to its potential of violating the Geneva Convention. The president of South Vietnam, Ngo Dinh Diem began to push the US Military Advisory Group in Vietnam and the White House to begin crop destruction in September 1961 but it was not until October 1962 when the White House gave approval for limited testing of Agent Blue against crops in an area believed to be controlled by the Viet Cong.  Soon after crop destruction became an integral part of the Ranch Hand program.

The targets for the spray runs were carefully selected to satisfy the strategic and psychological operations goals of the US and South Vietnamese military. The runs were surveyed to pinpoint the target area and then placed on a priority list. Due to the low altitude required for spraying, (ideally 150 feet above ground), the C-123s were escorted by fighter planes that would strafe or bomb the target area in order to draw out any ground fire if the area was believed to be 'hot'. Runs were planned to enable as straight a run as possible to limit the amount of time the planes were at low altitude. Data on the spray runs, their targets, the herbicide used and amount used, the weather and other details were kept and later put into a data base called the HERBICIDE REPORTING SYSTEM or HERBS tapes.

The effectiveness of the spraying was influenced by many factors including weather and terrain. Spray runs occurred during the early morning hours before temperatures rose above 85 degrees and the winds picked up. Mangroves in the Delta region required only one spraying and did not survive once defoliated. Whereas dense forests in the uplands required two or more spray runs. Within two to three weeks of spraying the leaves would drop from the trees which would remain bare until the next rainy season. In order to defoliate the lower stories of forest cover one or more follow-up spray runs were needed. About 10 percent of the trees sprayed died from a single spray run. Multiple spraying resulted in increased mortality for the trees as did following the herbicide missions with napalm or bombing strikes.

The End of the Operation

The use of herbicides in the Vietnam War was controversial from the beginning, particularly for crop destruction. The scientific community began to protest the use of herbicides in Vietnam as early as 1964 when the Federation of American Scientists objected to the use of chemical and biological weapons that they felt violated the Geneva Protocol of 1925. The American Association for the Advancement of Science (AAAS) issued a resolution in 1966 calling for a field investigation of the herbicide program in Vietnam. In 1967 seventeen Nobel Laureates and 5000 other scientists signed a petition asking for the immediate end to the use of herbicides in Vietnam. Press coverage of the controversial use of herbicides in Vietnam increased in the late 1960s.

In 1970 AAAS sent a team of scientists to conduct field test of the ecological impacts of the herbicide program in Vietnam. Parallel to these studies in 1969 a report authored by K. Diane Courtney and others found that 2,4,5-T could cause birth defects and still births in mice. This, and follow-up studies, led the US government to restrict the use of 2,4,5-T in the US in April 1970. The Department of Defense followed suit in Vietnam by 'temporarily' suspending the use of Agent Orange in Vietnam, though they continued to rely on Agent White for defoliation until supplies ran out and the last defoliation run took place on May 9, 1970. Sporadic crop destruction sorties using Agent Blue continued throughout 1970 until the final Ranch Hand run was flown on January 7, 1971.