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Institute of Medicine (US) Committee to Review the Health Effects in Vietnam Veterans of Exposure to Herbicides. Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam. Washington (DC): National Academies Press (US); 1994.

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Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam.

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3The U.S. Military and the Herbicide Program in Vietnam

From 1962 to 1971, the U.S. Air Force sprayed nearly 19 million gallons of herbicides in Vietnam, of which at least 11 million gallons was Agent Orange, in a military project called Operation Ranch Hand. An additional quantity (1.6 million gallons has been documented) of herbicides was applied to base perimeters, roadways, and communication lines by helicopter and surface sprayings from riverboats, trucks, or backpacks. Herbicide operations in Vietnam had two primary military objectives: (1) defoliation of trees and plants to improve observation, and (2) destruction of enemy crops.

Estimates of the number of U.S. military personnel who served in Vietnam during this period of herbicide use vary from 2.6 to 3.8 million. The total number of U.S. servicemen and women exposed to herbicides is also not known, although some individuals, such as those of the Air Force Operation Ranch Hand and the Army Chemical Corps, were more likely to have been exposed by the nature of their job assignments.

This chapter describes the characteristics of the Vietnam veteran population at potential risk of herbicide exposure during service in Vietnam, and reviews the U.S. military herbicide program of the 1960s and early 1970s. It summarizes what is known about the use of herbicides in Vietnam, their chemical formulations, and the quantities applied, and serves as background information for Chapter 6, which summarizes and evaluates the various methods for estimating exposure to herbicides in epidemiologic studies of veterans as well as other environmentally and occupationally exposed populations.


As one historian notes in his account of the Vietnam conflict, "there was no 'typical' U.S. soldier in Vietnam … the three million Americans who served there went through many varied experiences—partly because the quality of the war varied in different areas of the country, and partly because the nature changed over time" (Karnow, 1991). Individual experiences also varied according to job assignment, military unit of service, rank, and branch of service. Artillery units, for example, tended to be less mobile than cavalry because of the heavy equipment involved. An individual assigned to base headquarters with an Army personnel position experienced a different tour of duty than an infantry commander, a field engineer, or an officer stationed aboard a Navy vessel off the coast of I Corps. Personnel assigned to units in the Mekong Delta might slog week after week across paddy fields, while others patrolling the perimeters of major U.S. installations at Danang, Bien Hoa, and Camranh were often targets for sniper attacks (Karnow, 1991). Individuals and units also varied in their consumption of locally grown foods and water from local supplies, as well as in their personal hygiene practices. Ground forces—the Army and Marines—were likely to experience more of the day-to-day fighting than Navy or Air Force personnel (Card, 1983). Sociological assessments of the American soldier in Vietnam suggest that no one factor is more important in understanding the experiences of the individual veteran than the degree of exposure to combat (Moskos, 1975; Fischer et al., 1980; Martin, 1986; Shafer, 1990).

In order to properly evaluate existing epidemiologic studies of Vietnam veterans and to consider the possibility of new studies, the size and characteristics of the exposed population must be known. Remarkably, the number of U.S. military personnel who served in Vietnam during the Vietnam conflict is not known precisely. Estimates depend on definitions regarding time and place of service, and the source of the data on which the estimates are based. Although detailed records of demographic information were not compiled during the Vietnam era, some federal estimates are available. In addition, data from several national surveys of the Vietnam veteran population supplement the government estimates.

Estimates of the Number of Military Personnel Serving in Vietnam

According to official records, U.S. military advisory assistance to Vietnam began as early as 1950, during the First French-Indochina War; 128 personnel "spaces" were allotted for the U.S. advisory group (MACV, 1972). After the division of Vietnam along the seventeenth parallel in 1954, U.S. advisors were assigned the responsibility of training the South Vietnamese army. By the end of 1960, nearly 900 U.S. military advisors were stationed in the country—the vanguard of an estimated 2.6 to 3.8 million U.S. military personnel to serve in Vietnam over the next 13 to 15 years. Two advisors were killed in 1960 in a raid at Bien Hoa military base—the first American casualties of the Vietnam conflict (MACV, 1972).

As American concerns about Communist control of South Vietnam heightened, U.S. involvement increased. Toward the end of 1962, 11,000 U.S. military advisors and personnel were serving in South Vietnam, and the U.S. Military Assistance Command, Vietnam (MACV) was organized. During the next two and a half years, the number of personnel would increase to nearly 60,000 and America began bombing North Vietnam—first as "retaliation for North Vietnamese aggression" and ultimately, in February 1965, as a sustained activity (Shafer, 1990). Shortly afterward, President Lyndon Johnson ordered the deployment of U.S. military troops to South Vietnam (see Table 3-1).

TABLE 3-1. Summary of U.S. Military Strength in Vietnam and Quantities of Herbicides Sprayed: 1960-1973.


Summary of U.S. Military Strength in Vietnam and Quantities of Herbicides Sprayed: 1960-1973.

The Vietnam era was characterized by heavy conscription that began to gain momentum in 1965 (Card, 1983). Between 1964 and 1968, as American involvement in Vietnam escalated, U.S. troop strengths doubled, then nearly tripled, peaking at 543,482 in April 1969. The number of military personnel declined in the following years, in keeping with President Nixon's policy of "Vietnamization," falling to 475,000 at the end of 1969 and to 334,600 at the end of 1970. By the end of 1972, fewer than 25,000 American troops remained in Vietnam. The final U.S. withdrawal of American combat troops in Vietnam was completed in March 1973. The remaining Americans, including the ambassador to Vietnam, were evacuated from the U.S. embassy in Saigon in April 1975 (Karnow, 1991).

Although the military maintained accurate records of the number who died, reliable records-based information on the number and characteristics of men and women who served in the Vietnam conflict was more difficult to maintain during the wartime period. Because there is no master list of the millions of veterans who served during the Vietnam era, studies of Vietnam veterans must create their own sampling frames from which samples of veterans can be selected and from which national estimates can be generated. These estimates of the national Vietnam veteran population are necessary for epidemiologic studies of veterans that attempt to quantify the risk of various health effects for the entire veteran population-based on the results observed in representative samples. The extent to which the study sample is representative of the entire Vietnam veteran population in these epidemiologic studies is of utmost importance in designing programs to address the health needs of veterans (see Chapter 5 for further discussion of epidemiology and the evaluation of such studies).

The identification of an appropriate veteran group for study often involves a time-consuming and labor-intensive search of military records for names or Social Security numbers. The General Services Administration, under an agreement with the Department of Defense, maintains the military personnel records of veterans, including those from the Vietnam era at the National Personnel Records Center (NPRC) in St. Louis, Missouri. These records include military service information, on microfiche, for all American veterans. Once an individual has been identified by name or Social Security number, he or she can be matched to their military personnel file at NPRC. A computerized index lists the physical location of the individual's personnel file; the file can then be retrieved to verify the service information. It is currently impossible to readily determine from these records the true number of U.S. military personnel who served in Vietnam during the Vietnam era because this information has not been entered systematically into a computerized database.

Because of the difficulties in obtaining representative samples (and due to the nature of the question being examined), many studies do not attempt to generalize their findings to the entire veteran population, but rather focus on a discrete subpopulation of veterans, for example, U.S. Army ground combat troops who served in III Corps during 1967-1968, Marines who served in I Corps, or Air Force Operation Ranch Hand personnel. The results of such studies are limited to the group under study and do not necessarily apply to the entire Vietnam veteran population.

Comparison of the studies that do provide national estimates representative of the Vietnam veteran population is complicated, however, by differences in terminology and methodology. For example, the time and place of Vietnam service are not defined consistently across studies. Some studies define the Vietnam era as the period of service between August 1964 and June 1975. This period of service was defined as the "Vietnam era" by presidential proclamation on May 7, 1975 (Fischer, 1980). Others use January 1, 1965, to mark the beginning of the Vietnam era, and March 1973, the time of final withdrawal of combat troops, to designate its end. Yet other veteran population estimates refer to service in the "Vietnam theater" rather than Vietnam per se. The Vietnam theater includes Vietnam, Laos, Cambodia, and the adjacent waters of the South China Sea; service in Thailand may be also be included.

Estimates of the number of military servicemen and women who served during the Vietnam era are provided by several federal agencies, including the Department of Defense (DOD), the Department of Veterans Affairs (DVA), and the Department of Labor. A number of postwar surveys have also attempted to determine retrospectively, from samples of the veteran population, the total number of U.S. military personnel who served in Vietnam during the Vietnam era. A comparison of the differences in definition and methodology for deriving these estimates is provided below.

Federal Estimates

According to DOD calculations (Defense Almanac, 1992), 8.7 million served in the military during the Vietnam era (defined here as the period August 4, 1964, through January 27, 1973). The DOD estimates that 2.6 million, or approximately one-third, of these Vietnam era veterans served in Vietnam. Nearly 40 percent of Vietnam era veterans, or 3.4 million, served in the Vietnam theater (U.S. DOD, 1976). These estimates are based on military records tabulated by MACV from summaries prepared by individual units that recorded end-of-the-month troop numbers. Although the completeness of these records varied by unit, they are the best official documents available for estimating the number of U.S. servicemen in South Vietnam.

According to estimates of the Department of Veterans Affairs (DVA), approximately 8.3 million veterans of the Vietnam era (August 4, 1964, to May 7, 1975) were represented among the adult civilian U.S. population (U.S. VA, 1985). Approximately one-third, or some 2.7 million, of the Vietnam era veterans served in the Vietnam theater (defined as service in Laos, Cambodia, Vietnam, or the surrounding waters). The DVA adjusts its veteran population estimates based on the U.S. decennial census; estimates of Vietnam era service are based upon receipt of the Vietnam Service Medal, as identified on individual military discharge forms. Qualification for a service medal is limited to military units that supported operations within Vietnam and to those individuals that served in the Vietnam theater between July 1965 and April 1974 (Fischer et al., 1980). Therefore, the DVA estimate of the number who served in the Vietnam theater is restricted, based on use of the Vietnam Service Medal as an indicator of service.

Various demographic data on veteran populations, in addition to employment and disability statistics, are reported by the Bureau of Labor Statistics (BLS). These data, tabulated from the Current Population Survey (U.S. Department of Labor, 1992a,b), suggest that of the 7.9 million male veterans of the Vietnam era (August 1964 to May 1975), nearly one-half, or 3.7 million, reported having served in the Vietnam theater of operations (Vietnam, Laos, or Cambodia, or in the waters or air surrounding these countries). Estimates of the number of veterans who served in Vietnam per se are not available from these data.

Other Survey Estimates

Various other postwar surveys of Vietnam era veterans also provide estimates of the number who served. A 1979 Louis Harris survey of the U.S. adult, noninstitutionalized population who served on active duty in the military during the Vietnam era (defined as the period between August 1964 and June 1975) reported that approximately 3.8 million (42.5 percent of Vietnam era veterans) served in Vietnam (Fischer et al., 1980). An estimated 4.3 million, or 47.8 percent, of Vietnam era veterans reported service in the Vietnam theater during the Vietnam era.

The National Survey of the Vietnam Generation was conducted as part of the National Vietnam Veterans Readjustment Study (Kulka et al., 1988). The reference population for this survey was 8.3 million veterans who served during the Vietnam era (August 1964 to May 1975). According to these data, an estimated 3.1 million men and 7,000 women, or 37 percent of Vietnam era veterans, served in the Vietnam theater (defined as Vietnam, Laos, Cambodia, or the surrounding waters); nearly 2.6 million were stationed directly in Vietnam.

These various estimates of the Vietnam veteran population are summarized in Table 3-2. From these data, it is estimated that one-third to one-half of Vietnam era veterans, or 2.7 million to 4.3 million persons, served in the Vietnam theater of operations, depending on the definition of the period and/or location of military service. Comparable estimates of those who served in Vietnam range from 2.6 million to 3.8 million.

TABLE 3-2. Estimates (in millions) of the Vietnam Veteran Population.


Estimates (in millions) of the Vietnam Veteran Population.

Military and Demographic Characteristics

Selected military and demographic statistics on U.S. personnel who served in Vietnam are available from these official records and postwar surveys. According to BLS estimates of the veteran population in 1989-1990, veterans who were between 40 and 44 years of age comprise the single largest age cohort of male Vietnam era veterans; 38 percent of male Vietnam era veterans and 43 percent of male Vietnam theater veterans were born between 1946 and 1950 (see Table 3-3). These statistics on the current age distribution of Vietnam veterans corroborate findings from several recent veteran surveys (Fischer et al., 1980; Kulka et al., 1988; CDC, 1989; U.S. DVA, 1990).

TABLE 3-3. Age Distribution of Vietnam Era and Vietnam Theater Veterans 1989-1990 (numbers in thousands).


Age Distribution of Vietnam Era and Vietnam Theater Veterans 1989-1990 (numbers in thousands).

Some veteran surveys obtain information retrospectively on the veteran's background characteristics upon entering military service, whereas others describe the veteran's characteristics at the time of the survey (which could be 10 to 25 years after military discharge). Differences in sampling procedures limit comparisons of the surveyed populations. As discussed previously, some studies provide data only on Vietnam theater veterans, including those who served in Laos and Cambodia or other areas of Southeast Asia, depending on how theater is defined. Some studies do not include a comparison group of nonveterans or do not provide contrasts among various subgroups (i.e., race, branch or region of service), whereas others select only discrete groups for study (e.g., veterans of a particular age cohort or unit of service during a specific period of time). Furthermore, most surveys sample only males; less information on the characteristics of women who served in Vietnam is available (Schwartz, 1987). With these deficiencies in mind, estimates from several surveys involving large samples of veterans are presented below.

Approximately 50 percent of Vietnam era veterans served in the Army, 20 percent in the Navy, 20 percent in the Air Force, and the remaining 10 percent in the Marines or Coast Guard (Kulka et al., 1988). These data are in close agreement with DOD (Defense Almanac, 1992) estimates of the proportion serving by branch of service. Other than IV Corps, where 7 percent served, military personnel in Vietnam were relatively evenly distributed throughout the four military regions of the country. Approximately 80 to 85 percent of male Vietnam veterans were white, 10 to 12 percent black, and the remaining Hispanic or other (Fischer et al., 1980; Kulka et al., 1988; U.S. Department of Labor, 1990). Of those surveys that provided comparison groups, there were no differences in the racial composition of Vietnam era veterans compared to those who did not serve in Vietnam during the Vietnam era (Fischer et al., 1980; Card, 1983). Although race was not associated with military service, whites who did serve, and especially those who enlisted willingly, came from poorer families than whites who did not serve. For blacks, there were no significant socioeconomic differences between those who did and did not serve. However, blacks who served, and especially those who served more than two years, had completed more years of education than those who did not serve (Card, 1983).

Twenty percent of soldiers sent to Vietnam were assigned to combat units (Shafer, 1990), although surveys of veterans indicate much higher percentages who reported having experienced combat. A survey published by the Veterans Administration indicated that 70 percent of those sampled reported exposure to combat, which meant that they had come under some kind of attack (U.S. Department of Labor, 1990; Karnow, 1991). The CDC Vietnam Experience Study found that 57 percent of Army veterans had served in combat type units (i.e., infantry, artillery, armor, cavalry, and engineer; CDC, 1989).

The average age of those who experienced combat in Vietnam was 19 years, compared to 27 years in World War II (Shafer, 1990). Draftees were more likely to see heavy combat in Vietnam, compared to those who enlisted and served in other parts of the theater (Fischer et al., 1980; Kulka et al., 1988). No differences among racial or ethnic groups were found for either service in the Vietnam theater or exposure to combat. However, those who served in Vietnam with less than a high school education at the time of entry into military service were three times as likely to see heavy combat as those with college educations, and those who were less than 20 years of age at the time they went to Vietnam were twice as likely to be exposed to heavy combat as those aged 35 years or older (Fischer et al., 1980). A 1981 survey of a 1960 male high school cohort of military age during the Vietnam era found that veterans with lower academic aptitude, as measured by a series of cognitive tests scores received in the ninth grade, reported more combat experiences, such as seeing Americans wounded, firing a weapon at the enemy, or receiving fire from the enemy, than those with higher test scores (Card, 1983).

Just as there was no ''typical" American soldier or typical military experience in Vietnam, there was no one combat experience (Shafer, 1990; Karnow, 1991). The combat experiences of individual soldiers varied according to assignment, geographical region of duty, and the period during which they served. In addition, most soldiers who were sent to Vietnam after the first American troops arrived in 1965 were sent as individual replacements, rather than as units (Karnow, 1991). The military found it more efficient administratively to replace losses piecemeal than to replace units and rebuild them. Unfortunately, this operational strategy minimized prospects for unit cohesion and contributed to low troop morale (Shafer, 1990).

It should be noted that these estimates describe the surviving veteran population: more than 58,000 U.S. men and women were killed and over 300,000 were wounded, of which more than one-half were wounded seriously enough to require hospitalization (U.S. VA, 1985). The Combat Area Casualties Current File, maintained by the Department of Defense, contains records on U.S. personnel who died as a result of hostilities (killed in action, died from wounds, died while missing, or died while captured) or other causes (died from illness or nonhostile injury or other nonhostile causes) while serving in Cambodia, China, Laos, Vietnam, or Thailand during the conflict in Southeast Asia. As of November 1992, the file contained information on 58,166 deaths. Information potentially available in each casualty record includes branch of service, military grade and occupation code, birth date, cause and date of death, and length of service. Forty-four percent of the 58,166 U.S. military deaths occurred in those under age 21; three-fourths were aged 23 and younger. Among the recorded deaths, enlisted personnel suffered six times as many casualties as officers (86 percent and 14 percent, respectively), and pay grades E-3 and E-4 suffered the heaviest losses. The majority of deaths occurred among U.S. Army forces (66 percent), 25 percent occurred among the Marine Corps, 4.5 percent among the Navy, and 4.5 percent among the Air Force (U.S. DOD, 1986). As a group, Marines sustained the heaviest proportion of losses. Although blacks made up 11 percent of the American population and 12.6 percent of American forces in Vietnam, they accounted for 20 percent of Army combat deaths from 1961 to 1966 (Shafer, 1990). Black casualties ultimately accounted for 15.1 percent of total Army casualties and 13.7 percent of total U.S. casualties.

Studies of Women Veterans

There are no centrally maintained records or files of all women who were stationed in Vietnam during the Vietnam era (Thomas et al., 1991). The Veterans Administration (1985) reported that 263,000 women served in the military between 1964 and 1975 (the Bureau of Labor Statistics estimates that about 210,000 women served during the Vietnam era (U.S. Department of Labor, 1990); an estimated 5,000 to 7,000 women served in Vietnam (Thomas et al., 1991). Eight women were killed in Vietnam; all were nurses.

Very little information on the demographic characteristics of women veterans exists (Schwartz, 1987). The National Vietnam Veterans Readjustment Study (Kulka et al., 1988) sampled 736 Vietnam era female veterans, 432 of whom were Vietnam theater veterans. Over 70 percent of women who served in the Vietnam theater were born during the period 1940-1949. An estimated 97 percent were white. Nearly 80 percent served in the Army, 90 percent were officers, and 87 percent were military nurses (Kulka et al., 1988).

Thomas and colleagues (1991) conducted a study of 4,582 female Vietnam veterans who served between July 1965 and March 1973. The women were identified from the review of morning reports of Army hospital and administrative support units stationed in Vietnam, and from Air Force personnel files, Navy muster roles, and Marine Corps listings of all women assigned to Vietnam. More than 90 percent (93.9 percent) of the women in the study were white. They also tended, on average, to be older than male veterans; about one-third were younger than age 25 at the time they entered Vietnam service. Most female veterans (75 percent) served in the Army, followed by the Air Force (16 percent), Navy (8 percent), and Marines (less than 1 percent). Eighty percent of the female veterans included in this study were nurses. These estimates are similar to those determined by Kulka and colleagues (1988) in their review of women serving in the military during the Vietnam era.


In 1960, U.S. assistance to the Diem government in South Vietnam was limited to military advisors, economic aid, and some logistic support (Karnow, 1991). American military advisory forces in South Vietnam numbered fewer than 900 (MACV, 1972). Some leaders within the U.S. government and military warned that the time to act against a Communist takeover of South Vietnam had come and that further U.S. intervention was inevitable. Defoliation operations were among several supplemental actions proposed that could be conducted while decisions regarding the commitment of combat troops were pending (Buckingham, 1982). The use of herbicides in South Vietnam was recommended for several reasons: to remove foliage along thoroughfares used as cover for enemy ambushes, to defoliate vegetative areas surrounding enemy bases and communication routes, to improve visibility in heavily canopied jungle, and to destroy enemy subsistence crops (Collins, 1967; Huddle, 1969; U.S. Army, 1972). Although the first combat troops did not arrive in Vietnam until April 1965, preparations for the testing and conduct of a major aerial defoliation program proceeded in cooperation with the South Vietnamese government. In December 1961, President Kennedy authorized the use of herbicides, and on January 12, 1962, the first U.S. Air Force herbicide missions of Operation Ranch Hand were flown over South Vietnam (Warren, 1968; MACV, 1972).

Much of the currently available information on the military use of herbicides in South Vietnam during the period 1962 to 1971—the chemical formulations used, the quantities applied, the operational procedures for aerial spray missions, and the aircraft used—was compiled in the 1970s and early 1980s from military records kept during the conflict, DOD technical reports, and procurement records. In 1974, the National Academy of Sciences' Committee to Review the Ecological Consequences of Herbicides in Vietnam evaluated the available DOD records of herbicide spray missions conducted from 1965 to 1971. During the Vietnam era, thousands of pieces of information on fixed-wing herbicide spray missions from the MACV log books was compiled and recorded on the HERBS data tapes. The HERBS tapes are considered to contain the most complete, accurate, and authoritative compilation of data available on aerial fixed-wing herbicide operations conducted in Vietnam (Dashiell, 1973).

Herbicides were also applied by other methods. An unknown, but smaller, quantity of herbicides was applied around base perimeters and lines of communication to improve visibility and reduce the likelihood of enemy ambush. Records of these smaller-scale uses of herbicides were not systematically logged and do not appear on the HERBS tapes. A review of various Army records and military reports identified the use of an additional 1.6 million gallons of herbicides, and information on these sprays was recorded on the Services HERBS tape. Together these tapes of herbicide sprays account for approximately 20 million gallons of herbicides used in Vietnam from 1962 to 1971.

Operation Ranch Hand

The defoliation program in Vietnam began on December 4, 1961, when President Kennedy authorized the Secretary of Defense to test the military effectiveness of the defoliation of several lines of communication (MACV, 1968). Operation Ranch Hand, the tactical military project for the aerial spraying of herbicides in South Vietnam, was the first (and only) large-scale experience with chemical defoliants in U.S. military operations. According to MACV records, the first U.S. Air Force Ranch Hand missions over Vietnam were flown on January 12, 1962 (MACV, 1972); however, it was not until August 1962 that President Kennedy approved the program on a larger scale. The first major operation, to clear enemy infiltration routes, was carried out over the mangrove forests in the Ca Mau peninsula in the southernmost region of the Mekong Delta in September 1962 (Dux and Young, 1980).

Operation Ranch Hand had two primary objectives: (1) defoliation of trees and plants to improve visibility for military operations, and (2) destruction of essential enemy food supplies. Targets for defoliation by Ranch Hand included base camps and fire support bases (specifically constructed sites for storage of artillery in support of combat operations), lines of communication, enemy infiltration routes, and enemy base camps. Clearance of these areas improved aerial observation, opened roads to free travel, and hindered enemy ambush.

All large-area defoliation missions were flown exclusively by Ranch Hand crews (Collins, 1967). According to DOD records, the aerial application of herbicides was accomplished by spraying from C-123 fixed-wing aircraft and helicopters (UH-1 and H-34). During 1967-1968, requirements for herbicide missions increased to the point that the number of available C-123 aircraft was not sufficient to complete all approved targets within the desired time frame (MACV, 1968). In order to permit a more timely response to defoliation requirements, helicopter operations were recommended for smaller targets, such as in support of local base defense, maintenance of deforested areas, and the uncovering of known small ambush sites along lines of communication (MACV, 1968). As Ranch Hand operations declined in 1970-1971, the number of helicopter herbicide operations increased and gradually became the only aerial means of herbicide delivery.

With the buildup of American troops in 1965, Operation Ranch Hand also intensified: the number of C-123 aircraft assigned to the operation increased from 3 to 12 (36 aircraft were assigned to the program from 1967 until it was phased out in 1971); permanent personnel were assigned to the team (Dux and Young, 1980); and the number of missions increased nearly sixteenfold from 107 in 1962 to more than 1,600 in 1967 (Huddle, 1969; NAS, 1974). Typical missions early in the conflict included 3 to 4 aircraft, increasing to as many as 19 in the later years. The operation of a single aircraft was termed a sortie. In the period from 1966 through 1968, more than one sortie per day was often common. During the first six months of 1968, the 24 C-123 aircraft assigned to Ranch Hand averaged nearly 39 sorties per day (Young et al., 1978). All missions within a target area formed a project (Young and Reggiani, 1988). Ranch Hand missions were also frequent targets of ground fire due to the low altitude and slow speed of the aircraft, and flights required fighter cover for protection (Collins, 1967; Warren, 1968; Spey, 1993). As early as 1963, fighter cover was used in conjunction with defoliation missions to provide mission protection. In 1966, it was reported that nearly one-third (29 percent) of all C-123 defoliation sorties received "hits" from ground fire. The ratio of hits per sortie decreased in later years with improved fighter tactics (Warren, 1968). The helicopter delivery system was also particularly vulnerable to ground fire because of the slow delivery speed (Collins, 1967).

The control of the use of herbicides was a joint effort by the government of South Vietnam and the United States. Authorization in Saigon and at the Corps level was mandatory for all Ranch Hand crop destruction and defoliation operations by fixed-wing aircraft (MACV, 1969b; NAS, 1974). The authorization procedure required approval prior to spraying by the Government of Vietnam (local and national); the U.S. Ambassador; and the commander of the U.S. Military Assistance Command, Vietnam. Procedures governing these herbicide operations required that all herbicide spraying be "limited to areas of low population" and that "defoliation operations not normally be undertaken when it is apparent that damage will occur to crops … unless the military advantage is very clear" (MACV, 1969b).

Following each Ranch Hand mission a report was to be filed that included information on the number of aircraft scheduled and the number productive, the type and number of gallons of herbicide sprayed, the type of mission (crop destruction or defoliation), and the location of the spray run.

The normal altitude of the C-123 for spray application was 150 feet, flying at a speed of 130 to 150 knots, and producing a swath width of 240 m per aircraft (MRI, 1967; NAS, 1974). Under these ideal conditions, a 1,000 gallon tank permitted a 3- to 4-min spray time at a total distance of about 8.7 statute miles, or about 340 acres treated per aircraft, with a deposition rate of 3 gallons per acre (Young et al., 1978). The HIDAL (Helicopter, Insecticide Dispersal Apparatus, Liquid) was initially developed as a potential insecticide delivery system. The capacity of the UH-1 spray tank was 200 gallons, but because of weight limitations, only 100 gallons was carried. The helicopter spray system was capable of depositing 1.5 gallons per acre when flown at 55 knots and cut a swath of 75 m.

In addition to aircraft altitude and speed, distribution of the spray was also affected by climate, wind, terrain, and turbulence from the aircraft. Although missions generally were flown in the early morning when the wind was calm, to minimize spray drift, the NAS (1974) study showed that crop damage resulting from drift on defoliation missions was greater than that caused by crop destruction missions—indicating that widespread crop damage resulted from drift. Maximum defoliation results were achieved during the growing season, when the vegetation was in full-leaf and actively growing (Young et al., 1978). The rainfall pattern (in relation to the fastest growing season), the vegetation composition, and the number of canopies were important in determining the proper herbicidal agent and the number of applications required to uncover completely the ground underneath (U.S. Army, 1972). Tschirley (1967) estimated that in a moist, tropical, triple-canopy forest, approximately 80 percent of the spray droplets were intercepted by the uppermost canopy, 14 percent fell to the inner level, and only 6 percent reached ground-level vegetation (Tschirley, 1967). Air turbulence from the aircraft also helped to distribute spray droplets throughout the foliage and was an important factor in the dispersal of the spray (MRI, 1967).

Ranch Hand aircraft were also responsible for the spraying of insecticides to control malaria-carrying mosquitoes, and began spraying in South Vietnam in 1966. According to Air Force records, Ranch Hand "silver bugs" flew approximately 20 insecticide sorties per month in 1967. One sortie could cover about 15,000 acres. They were commonly spotted over allied camps, spraying malathion and DDT (dichlorodiphenyltrichloroethane). The insecticide delivery planes were not camouflaged like the other Ranch Hand C-123 aircraft. The spraying involved longer missions; therefore, fuel conservation was a concern. On the other hand, navigation of the insecticide sprays along exact coordinates was not as vital as for the herbicide missions (Collins, 1967; Buckingham, 1982: Young and Reggiani, 1988). It was reported that 44 percent of the land area of Southeast Asia (primarily South Vietnam) was sprayed with malathion (Westing, 1984).

Herbicide Formulations

Four major compounds were used in the Ranch Hand herbicide formulations—2,4-D (2,4-dichlorophenoxyacetic acid), 2,4,5-T (2,4,5-trichlorophenoxyacetic acid), picloram, and cacodylic acid. These compounds have been used worldwide for the control of weeds and unwanted vegetation, although the application of 2,4,5-T is no longer permitted in the United States following a series of Environmental Protection Agency directives in the 1970s. A considerable amount of information is available on the physical, chemical, and toxicological properties of these compounds, although it is greater for 2,4,5-T and 2,4-D than for picloram and cacodylic acid (see Chapter 4).

The term herbicide includes chemicals that regulate normal plant growth. Some organic chemicals are considered growth regulators and are effective in minute amounts at stimulating or inhibiting plant growth. Some herbicides, such as 2,4-D, stimulate plant growth when applied at extremely low dosages, but inhibit growth or are lethal at higher concentrations.

Herbicides may be classified on the basis of their effects on plants and their site of application (foliage or soil). Selective herbicides may kill some plants and cause little or no damage to other plant species. By contrast, nonselective herbicides exhibit a broad spectrum of herbicidal effects on most plant species (Huddle, 1969; U.S. Army, 1970). Foliage-applied herbicides include contact herbicides or desiccants, which kill primarily by contact with plant tissues, and systemic herbicides, which are absorbed and translocated within the plant from the point of entry. Soil-applied herbicides kill germinating seeds and established plants by uptake of the chemical from the soil.

Which of these four major chemicals (2,4-D, 2,4,5-T, picloram, or cacodylic acid) was chosen for a specific application depended on the desired effects. 2,4-D and 2,4,5-T are chlorinated phenoxy acids, and each is effective against a wide array of broadleaf plant species (Irish et al., 1969). They persist in soil only a few weeks (Buckingham, 1982). Picloram, like 2,4-D and 2,4,5-T, regulates plant growth. Compared to 2,4-D, picloram is more mobile, and therefore better able to penetrate the plant's roots and be transported throughout the plant's tissues. Unlike the phenoxy herbicides, picloram is extremely persistent in soils. The fourth compound, cacodylic acid, contains an organic form of arsenic. Cacodylic acid is a desiccant, causing a plant's tissues to lose their moisture and eventually killing the plant. It is a contact herbicide that is rapidly rendered ineffective in soil.

Military Herbicides

The major herbicides employed in Operation Ranch Hand were code named according to the color of an identification band painted on the 55 gallon storage drum. Agents Purple and Blue were the first defoliants introduced into Vietnam in 1962. Agent Purple was a 50:30:20 mixture of the n-butyl ester of 2,4-D, and the n-butyl and isobutyl esters of 2,4,5-T (see Table 3-4). Purple was first tested in the Camp Drum, New York, defoliation test in 1959 and found to be most effective on broadleaf plants. Young and colleagues (1978) reported that 145,000 gallons of Agent Purple was procured and applied in Vietnam during 1962-1964. Because of its volatility, Agent Purple was replaced by Agent Orange in 1965.

TABLE 3-4. Major Herbicides Used in Operation Ranch Hand: 1962-1971.


Major Herbicides Used in Operation Ranch Hand: 1962-1971.

Blue was the code designation for a liquid formulation of cacodylic acid and its sodium salt. The term Blue was first applied to cacodylic acid in a powder form that was mixed in the field with water. It was later replaced by the liquid formulation Phytar 560-G. Cacodylic acid is a highly soluble organic arsenic compound that is readily broken down in soil. According to military herbicide records, more than 1.1 million gallons of Agent Blue was dispensed in the DOD herbicide program. Approximately one-half of all Agent Blue was used for crop destruction missions; it was the agent of choice for destruction of rice crops. Blue was employed in situations requiring rapid defoliation, causing noticeable browning or discoloration in one day, with maximum desiccation and leaf fall occurring within two to four weeks (Darrow et al., 1969). The remainder was used in defoliation or sprayed around base perimeters, being delivered by helicopters or ground vehicles with sprayers attached to them (Young et al., 1978).

Agents Pink and Green were used in small quantities; however, official records of herbicide sprays during the early years of the program (1962-1964), when these two herbicides were used, are incomplete. Young and colleagues (1978) reported the use of 122,792 gallons of Agent Pink, a 60:40 mixture of the n-butyl ester and isobutyl ester of 2,4,5-T. Pink had been previously tested in the 1953-1964 defoliation program in Thailand (U.S. Army, 1965). Agent Green was a single-component formulation of the n-butyl ester of 2,4,5-T. Slightly more than 8,000 gallons of Agent Green was sprayed, primarily in defoliation missions (Young et al., 1978).

In January 1965, two additional herbicides, code named Orange and White, were introduced into the herbicide program. Agent Orange, a 1:1 mixture of 2,4-D and the n-butyl ester of 2,4,5-T, accounted for approximately 61 percent of the recorded herbicide use. Orange was the general-purpose herbicide for defoliation and crop destruction, with leaf fall in three to six weeks and control persisting for seven to twelve months. According to military estimates of herbicide use, 90 percent of Agent Orange was used in Ranch Hand forest defoliation missions; 8 percent was used in Ranch Hand crop destruction missions; and 2 percent was sprayed from the ground around base perimeters and cache sites, waterways, and communication lines (NAS, 1974). Mangrove forests were especially sensitive to the effects of Agent Orange—a single application killed them (NAS, 1974). Annual crops were killed rapidly by one application of Agent Orange; root and tuber crops, and perennial and woody tropical crops such as jackfruit, papaya, and mango, were also susceptible to Agent Orange (Young et al., 1978).

Orange II was introduced later in the program. It differed from the original Agent Orange in that the n-butyl ester of 2,4,5-T was replaced by the isooctyl ester; however their herbicidal effects were similar. According to procurement records, less than 10 percent of the total Agent Orange used was Orange II (Craig, 1975).

White was the code name for Tordon 101, a liquid mixture of 2,4-D and picloram. Approximately 5.25 million gallons of Agent White was dispensed during Ranch Hand operations. More than 95 percent of Agent White was applied in defoliation missions (NAS, 1974; Young and Reggiani, 1988). Because of the persistence of Agent White in soil, it was not recommended for use on crops, but was most often used in areas where longer persistence rather than immediate defoliation was desired, such as inland forests. White was effective principally on broadleaf herbaceous and woody plants. The herbicide's action on woody plants was usually slow, however, and full defoliation did not normally occur for several months (Young and Reggiani, 1988).

In addition to these four major compounds, Dinoxol, Trinoxol, and diquat were applied on native grasses and bamboo (Brown, 1962). Soil-applied herbicides were also reportedly used around base camp perimeters, mine fields, ammunition storage areas, and other specialized sites requiring control of grasses and woody vegetation (Darrow et al., 1969). Additional accounts include the use of fungicides, insecticides, wetting agents, wood preservatives, insect repellents, and other herbicides (Gonzales, 1992). The number of military personnel potentially exposed to these chemicals is not available.

An undetermined amount of herbicides and insecticides was procured and distributed by Australian forces in Vietnam during 1966-1971. The use of these chemicals was confined largely to defoliation around base camps, improving security, and controlling mosquito-borne diseases. It appears that the chemicals were largely dispersed by use of ground delivery techniques, although low-volume aerial applications of insecticides, usually by helicopter, have been reported. The chemicals tested and used included 2,4-D, chlordane, DDT, diazinon, lindane, malathion, and picloram (Australian Senate Standing Committee, 1982).

Level of Toxic Contaminants

2,3,7,8-TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) is a contaminant of 2,4,5-T, but not of 2,4-D, and is a very toxic material. The levels of TCDD found in any given lot of 2,4,5-T depend on the manufacturing process (Young et al., 1976), and different manufacturers produced 2,4,5-T with various concentrations of TCDD. The primary source of 2,4,5-T in the herbicides used in Vietnam was Agent Orange. It is the unknown concentration of TCDD in Agent Orange that is of particular concern.

Of all the herbicides used in South Vietnam, only Agent Orange was formulated differently from the materials for commercial application that were readily available in the United States (Young et al., 1978). TCDD concentrations in individual shipments were not recorded, and levels of TCDD varied in sampled inventories of herbicides containing 2,4,5-T. Analysis of the TCDD concentration in stocks of Agent Orange remaining after the conflict, which had either been returned from South Vietnam or had been procured but not shipped, ranged from less than 0.05 to almost 50 parts per million (ppm), averaging 1.98 and 2.99 ppm in two sets of samples (NAS, 1974; Young et al., 1978). Comparable manufacturing standards for domestic use of 2,4,5-T in 1974 required that TCDD levels be less than 0.05 ppm (NAS, 1974). Therefore, depending on which stocks were sampled, the level of dioxin contamination in Agent Orange could have been up to 1,000 times higher than the level of dioxin found in phenoxy herbicides domestically available at the time.

Agents Green, Pink, and Purple, also contained 2,4,5-T and were used from 1962 through mid-1965. These 2,4,5-T formulations used early in the program (prior to 1965) contained 16 times the mean dioxin content of formulations used during 1965-1970 (Young et al., 1978). Analysis of archive samples of Agent Purple reported levels of TCDD as high as 45 ppm (Young, 1992). The mean concentration of TCDD in Agent Purple was estimated to be 32.8 ppm and in Agents Pink and Green, 65.6 ppm (Young et al., 1978).

Termination of the Program

After a relatively slow buildup in military herbicide operations from 1962 to 1965, herbicide use increased rapidly during 1966 and 1967, was relatively stable in 1968 and 1969, and then dropped sharply in 1970. According to information on Ranch Hand spray missions, 80 percent of herbicides sprayed in the herbicide program (1962 to 1971) were applied during the period from 1966 to 1969.

As the military use of herbicides in Vietnam intensified, various questions were raised concerning the legality, morality, and possible long-term consequences of the program. By the end of the decade, the controversy had become a contributing element in the growing opposition to American involvement in Vietnam. The crop destruction program was of particular concern. Official military reviews of the herbicide program frequently cited the appearance of adverse political and psychological effects from the military operations on the civilian population in North Vietnamese-controlled areas (Warren, 1968).

In October 1969, the Department of Defense restricted the use of Agent Orange to areas remote from populations. This action was prompted by a National Institutes of Health report that 2,4,5-T could cause malformations and stillbirths in mice. At about the same time it was recognized that 2,4,5-T was contaminated with TCDD. In December 1969, the American Association for the Advancement of Science (AAAS) declared that recent research showing that 2,4-D and 2,4,5-T could cause birth deformities in experimental animals supported the conclusion that 2,4,5-T posed a probable health threat to humans. The AAAS also maintained that the levels of application of 2,4-D and 2,4,5-T in Vietnam exceeded levels in civilian usage and called on the Department of Defense to cease use of these chemicals (Buckingham, 1982). In April 1970, the Secretaries of Agriculture; Health, Education, and Welfare; and the Interior jointly announced the suspension of certain uses of 2,4,5-T (Young et al., 1978). The Department of Defense temporarily suspended all use of 2,4,5-T (and therefore Agent Orange) in all military operations pending ''further evaluation of its chemical constituents" (U.S. GAO, 1978). Since Agent Orange was no longer available for military use, all defoliation missions were shifted to Agent White, but White was not as desirable for military purposes because defoliation required four months with White compared to three to four weeks with Orange (Buckingham, 1982). In May 1970, Ranch Hand flew its last defoliation (but not crop destruction) mission in Vietnam.

According to Department of Defense records, on February 12, 1971, MACV further announced that herbicides would no longer be used for crop destruction in Vietnam, and the last fixed-wing herbicide-dispensing aircraft was flown. Subsequent herbicide operations (Agents Blue and White) were limited to certain strictly controlled use around allied fire bases by helicopter or on the ground (MACV, 1972). The last U.S.-authorized helicopter herbicide operation was flown on October 31, 1971 (NAS, 1974).

Disposal of Surplus Herbicides

In 1977, the U.S. Air Force (USAF) disposed of 2.22 million gallons of Agent Orange by incineration at-sea (Young et al., 1978). This operation, known as PACER HO, was accomplished under strict criteria of the U.S. Environmental Protection Agency (EPA) ocean dumping procedures. In order to obtain an ocean dumping permit, the EPA required the USAF to conduct extensive research on the environmental impact and occupational safety of the land transfer and loading operations and of shipboard incineration operations (Young et al., 1978).

When the Department of Defense suspended the use of 2,4,5-T in April 1970, the U.S. Air Force "had an inventory of 1.37 million gallons of [Agent] Orange in South Vietnam and 0.85 million gallons at the Naval Construct Battalion Center in Gulfport, Mississippi" (Young et al., 1978). In September 1971, the Department of Defense directed that all surplus Agent Orange in South Vietnam be removed and that the entire 2.2 million gallons be disposed of by an environmentally acceptable method. The 1.37 million gallons in South Vietnam was moved to Johnston Island, in the Pacific Ocean, for storage (Buckingham, 1982). The USAF reviewed various methods for the destruction and recovery of surplus Agent Orange. Techniques reviewed for destruction included soil biodegradation, high-temperature incineration, deep well injection, burial in underground nuclear test cavities, sludge burial, and microbial reduction (Tremblay and Virost, 1977). Techniques reviewed for recovery of a useful product included return to manufacturers, fractionation, and chlorinolysis (Tremblay and Virost, 1977). The USAF decided that destruction by high-temperature incineration was the method that warranted further research.

Although the DOD directed the Air Force to dispose of all remaining drums of Agent Orange in 1971, it was not until 1974 that a plan was offered for disposal of the 2.2 million surplus gallons of herbicide. On April 7, 1977, the EPA issued a research permit to the USAF and Ocean Combustion Service allowing the transport of Agent Orange from Gulfport, Mississippi, to a site in the North Pacific Ocean for the purpose of at-sea incineration. The USAF contracted with the German-built, Dutch-owned incineration ship, the Vulcanus, in accordance with the provisions of the Marine Protection, Research and Sanctuaries Act of 1972 (Tremblay and Virost, 1977). The entire operation required three ship loadings (one from Gulfport and two from Johnston Island) for the total surplus of Agent Orange to be incinerated.

Ground Spraying of Herbicides

Although the number of U.S. military personnel exposed to herbicides is impossible to determine precisely, the majority of those assigned to Operation Ranch Hand can be presumed to have been exposed to Agent Orange and other herbicides. During the entire operation, approximately 1,250 military personnel served in Ranch Hand units. Although the Air Force maintained complete records of its Operation Ranch Hand fixed-wing herbicide missions, documentation of spraying conducted on the ground by boat, truck, or backpack and authorized at the unit level was less systematic. Authorization for herbicide missions by helicopter or surface spraying from riverboats, trucks, and hand-operated backpacks was delegated to the Republic of Vietnam and U.S. authorities at the Corps level; these operations required only the approval of the unit commanders or senior advisors. "Free-spraying" areas, including the Demilitarized Zone (DMZ) at the seventeenth parallel and the first 100 meters outside base camps, were also exempt from Ranch Hand regulations (NAS, 1974). This delegation of authority for spraying to the Corps level reduced the lag time that existed from proposal to completion of small defoliation projects, such as around depots, airfields, and outposts (Collins, 1967). However, because these helicopter and ground sprays were less rigidly controlled than fixed-wing aerial sprayings, the recording of such sprays was not as systematic as those of Operation Ranch Hand.

The U.S. Army Chemical Corps, using hand equipment and H-34-type helicopters, conducted smaller spray operations, such as defoliation around Special Forces camps; clearance of perimeters surrounding airfields, depots, and other bases; and small-scale crop destruction (Warren, 1968; Thomas and Kang, 1990). Twenty-two Army Chemical Corps units were assigned to South Vietnam between 1966 and 1971. Approximately 950 veterans who served in the Army Chemical Corps in Vietnam between 1966 and 1971 have been identified from unit morning reports. Men serving in these units were trained in the preparation and application of chemicals, as well as in the cleaning and maintenance of the spray equipment (Thomas and Kang, 1990).

Units and individuals other than the members of the Air Force Ranch Hand and Army Chemical Corps were also likely to have handled or sprayed herbicides around bases or lines of communication. For example, Navy riverine patrols were reported to have used herbicides for clearance of inland waterways. Engineering personnel required the use of herbicides for removal of underbrush and dense growth in constructing fire support bases. It is estimated that 10 to 12 percent of the total volume of herbicides was dispensed from the ground by spraying from backpacks, boats, trucks, and buffalo turbines (NAS, 1974). The buffalo turbine was a trailer-mounted spray system used for roadside spraying and perimeter applications, which essentially "shot" the herbicide with a velocity up to 240 km/hour and a volume of 280 m3/min (Young and Reggiani, 1988). Hand spray units consisted of a backpack type of dispenser with a capacity of 3 gallons (Collins, 1967).

Although some information is documented in military records, it is impossible to determine accurately from military records alone the extent of spraying conducted on the ground or the number of personnel involved in these operations with potential herbicide exposure. An unknown number of non-Ranch Hand personnel likely received various degrees of exposure to herbicides. Young and Reggiani (1988) report that the actual number "may be in the thousands since at least 100 helicopter spray equipment units were used in South Vietnam, and most military bases had vehicle-mounted and backpack spray units available for use in routine vegetation control programs." The dregs of the 55 gallon drums were pumped into smaller drums and sent to military camps for local defoliation of crops and control of perimeter foliage (Dux and Young, 1980).

According to official documents, the "small-scale use of herbicides, for example around friendly base perimeters, were at the discretion of area commanders. Such uses seemed so obvious and so uncontroversial at the time that little thought was given to any detailed or permanent record of the uses or results" (U.S. Army, 1972). The Department of Defense took few precautions to prevent troops' exposure to herbicides since they were considered to be a low health hazard. Precautions prescribed were consistent with those applied in the domestic use of herbicides existing before the Vietnam conflict (U.S. GAO, 1979b). The Army added that exposure of ground troops was very unlikely since DOD personnel did not enter a Ranch Hand-sprayed area until approximately four to six weeks after the mission, when defoliation was complete and the herbicide was biodegraded or photodegraded (U.S. Army, 1972). The restriction placed on troops' entering a previously sprayed area was primarily for operational reasons, to prevent troops from being injured by the fighter aircraft that often accompanied the herbicide spraying aircraft (U.S. GAO, 1979b).

The 1979 study by the U.S. General Accounting Office (U.S. GAO, 1979b) examined the military defoliation operation in the Con Thieu province of I Corps between January 1966 and December 1969. During this period, more than 2 million gallons of herbicides were sprayed in I Corps. By using average troop strength and turnover figures, an estimated 218,000 Marine infantry personnel were determined to have been assigned to I Corps between 1966 and 1969. By randomly selecting 276 of 976 Marine monthly battalion reports, the GAO tracked troop movement and compared troop locations with herbicide mission data. Nearly 26,000 U.S. Marines and Navy medical personnel were identified who entered within a radius of 2.5 km of the defoliated target areas within one day of spraying; 4,300 troops were identified as being within 0.5 km of the flight path; 11,700 were within 2.5 km within four weeks. In the Khe Sanh-Thon Son Lam area, an estimated 4,300-8,000 troops were within 0.5 km of the sprayed area within one day of spraying; within 28 days, 33,600-45,300 troops were determined to have been within 2.5 km of the defoliation target. Army records were found to lack sufficient information, so that estimates of the number of Army personnel close to sprayed areas could not be calculated. The GAO report concluded that "the chances that ground troops were exposed to herbicide Orange are higher than the DOD previously acknowledged … the group of personnel most likely to have been exposed could include ground troops as well as herbicide handlers and aircraft crew members" (U.S. GAO, 1979b).

The HERBS and Services HERBS Tapes

A log of the aerial herbicide applications was maintained by the Chemical Operations Division, United States MACV, from data received from the various bases that supported herbicide missions. These records became the source documents for HERBS, the computerized system for processing, storing, and retrieving monthly herbicide mission activity data. HERBS was designed and implemented for the Chemical Operations Division by the Data Management Agency, MACV, in May 1970 (MACV, 1970).

Data received from the field were processed on a mission-by-mission basis. For each aerial herbicide mission between July 1965 and February 1971, information was recorded on the type of herbicide; the number of gallons sprayed; the number of scheduled, actually flying, and productive aircraft; the mission flight path coordinates; the province in which the mission flew; the purpose of the mission (defoliation or crop destruction); and the number of aborts. Flight paths were identified by the UTM (Universal Transverse Mercator) coordinates, a standard grid system for identifying geographic points.

In 1974, the DOD furnished a version of the HERBS tapes to a NAS committee acting under a congressional mandate to study the ecological effects of herbicide use in South Vietnam (NAS, 1974). The tapes provided by DOD included the date, mission number, location (UTM coordinates), type, and quantity of herbicide; the area covered; the purpose of mission for fixed-wing operations during the period August 1965 (when the logbook was started) through February 1971; and helicopter crop destruction missions flown from 1968 to 1971 (NAS, 1974). Additional printouts of the number of aircraft per mission and of herbicide missions conducted during March through October 1971, the stated termination of the U.S.-controlled herbicide operations, were also provided. The committee conducted an inventory of the herbicide operations and constructed maps of the herbicide missions based on data recorded on the HERBS tapes.

The HERBS tapes contain information on 6,539 herbicide missions and 17.6 million gallons of herbicides sprayed during operations for the period August 1965 through February 1971. Nearly 11.3 million gallons and 4,109 missions involved Agent Orange, 5.2 million gallons and 1,786 missions Agent White, and 1.1 million gallons and 640 missions Agent Blue. Nearly 70 percent of all missions (15.5 million gallons) were for defoliation, 13 percent were crop destruction missions (1.6 million gallons), and the remaining 17 percent were flown over or around base perimeters, cache sites, communication routes, and waterways (0.5 million gallons).

Certain deficiencies in the HERBS data were noted by the NAS committee. These deficiencies were associated with errors in transcription of the records to IBM punch cards, and incomplete or illegible listings; erroneous recording of flight paths, particularly for crop destruction missions when sprays were frequently shut off between targets, or when flying over mountainous terrains or along winding riverbeds; lack of information on herbicide missions before and after the 1965-1971 period; no records of chemical "dumps"; and no records of herbicide missions authorized by the Corps level (these would include defoliation missions by helicopter and sprays made by land or water-borne equipment). Because of the lack of information on these uses of herbicides, the NAS committee estimated that an additional 2.4 million gallons of herbicides may not be accounted for by the HERBS tapes (NAS, 1974).

The NAS committee compared the inventory of herbicide missions with procurement records of the DOD. The total number of gallons of herbicides sprayed as recorded on the HERBS tapes was nearly identical to the amount procured, 17.63 million gallons and 17.58 million gallons, respectively.

In 1986, the U.S. Army Joint Services Environmental Support Group recorded an additional 1.6 million gallons of herbicides sprayed from a review of U.S. Army Chemical records and various documentation on helicopter, backpack, and other types of ground sprays (see Table 3-5). Some of this usage was either improperly recorded, incompletely documented, or omitted from the HERBS tapes (U.S. Army and Joint Services ESG, 1986; Young and Reggiani, 1988). The resulting computer tape was named the Services HERBS tape since it was thought that the records of other services would show ground spray operations; only one Navy mission, however, could be documented from available records (U.S. Army and Joint Services ESG, 1986). The Services HERBS tape contains data on helicopter spray missions prior to 1968, backpack, and other ground sprayings by Army personnel. When combined with the HERBS tapes on herbicide operations from August 1965 through February 1971, these two tapes account for 19.2 million gallons of herbicides sprayed in Vietnam.

TABLE 3-5. Quantity of Herbicides Recorded on the Services HERBS Tape (gallons).


Quantity of Herbicides Recorded on the Services HERBS Tape (gallons).

Geographical Distribution of Herbicide Sprays

South Vietnam was divided into four combat tactical zones, from I Corps lying south of the DMZ to IV Corps in the Mekong Delta region (Figure 3-1). Although spraying occurred in most provinces of Vietnam, certain areas of the country were subject to more intensive spraying. The herbicide mission maps (Figure 3-2) indicate that defoliation missions were not uniformly distributed but were concentrated in certain geographical areas—along transportation routes, in occupied areas around Saigon, and on infiltration routes along the Laotian and Cambodian borders and the DMZ where enemy attacks were likely (U.S. Army, 1972). Primary target areas for crop destruction missions were in I Corps and along the upland and mountain valleys of II Corps (NAS, 1974). The military purposes of these missions were to deny food to the enemy, to redirect enemy manpower to crop production, and to weaken enemy strength in these areas (Warren, 1968).

FIGURE 3-1. South Vietnam during the Vietnam conflict.


South Vietnam during the Vietnam conflict.

According to a 1972 Department of the Army report, Herbicides and Military Operations, the dense forest along many of the key marine and land transportation routes served as effective cover for enemy ambush (U.S. Army, 1972). In particular, the Rung Sat Special Zone, an area of dense mangrove forests, afforded enemy concealment along the main shipping route to Saigon. Defoliation of the area began in the mid-1960s, and by the late 1960s, most of the mangrove forests adjacent to the shipping routes were defoliated. The defoliation operation was so complete that it eliminated enemy attacks on shipping in the Rung Sat area (U.S. Army, 1972).

Infiltration of the enemy and their supplies into Vietnam was also a major problem for military operations. The predominant points of entry were in densely forested areas, where U.S. patrols were subject to enemy ambush, and the forest cover concealed the enemy and its supplies. The Ca Mau peninsula was a temporary staging area for infiltration into the Mekong Delta and for attacks on local shipping and Navy patrol craft along the peninsula's streams and canals. Defoliation operations in 1967 and early 1968 aided military operations by improving observation of formerly heavily forested jungle areas (U.S. Army, 1972).

The enemy infiltration terminated in base camps within South Vietnam; several were located near the Cambodian border and others were located near Saigon. These enemy camps were the source of raids on and harassment of friendly forces, terrorist attacks on local inhabitants, and attempted infiltration into cities. War Zone C (an area in III Corps on the Cambodian border), and War Zone D and Bear Cat (both near Saigon), were three such enemy base camp areas noted by the Army that were sprayed repeatedly to reach all levels of the canopy forest and restrict regrowth.

Perimeter spraying by hand or helicopter at base camps and other installations was required to control the growth of tall grasses and brush. In areas where bamboo or tall grass surrounded a base, it was necessary to respray every two or three months to keep the vegetation low; however, the Army notes that in most locations, the topography, hazardous conditions, mine fields, and limited work force and equipment precluded the use of hand sprays for clearing base perimeters (U.S. Army, 1972).

Crop destruction targets were primarily located in I Corps and the western region of II Corps. Rice was the main target for destruction, and Agent Blue was found to be most effective. Although the immediate effect of the herbicides was to destroy the rice crop, the Army reported that new crops could be planted during the next growing season due to the lack of residuals in the soil that restricted subsequent plant growth.

Assuming a flight swath width of 80 m, the NAS estimated that from 1965 to 1971, 3.6 million acres, or nearly 10 percent of the land area of South Vietnam, had been sprayed at least once with herbicides (NAS, 1974). About 1.2 million acres, or roughly 34 percent of the sprayed area, was sprayed more than one time. These calculations are based on figures for the spraying missions by the C-123s and do not take into account unrecorded helicopter or ground sprays, or the effects of wind drift, aircraft speed, and rates of delivery. III Corps was the most heavily sprayed area of Vietnam, receiving about 53 percent of all herbicide sprays from 1965 to 1971 (Table 3-6). Thirty percent of III Corps was sprayed at least once (Westing, 1984). War Zones C and D, and the Iron Triangle in III Corps, can also be identified as heavily sprayed areas in maps of herbicide defoliation missions. The Rung Sat Special Zone in III Corps near Saigon, where the Saigon and Dong Nai Rivers linked together, was the most heavily sprayed region in Vietnam, as well as a site of frequent U.S. Navy operations. In 42 missions, the C-123s sprayed thousands of gallons of herbicides on the mangrove swamps to flush out Vietcong from hidden strongholds, from which they attacked supply ships and instituted offensives in the Delta region and surrounding provinces (Dux and Young, 1980). The area was sprayed consistently until 1970; the NAS (1974) estimated that 57 percent of the Rung Sat Special zone had been sprayed.

TABLE 3-6. Herbicide Use by Military Region, 1965-1971 (million gallons).


Herbicide Use by Military Region, 1965-1971 (million gallons).

FIGURE 3-2a. Herbicide defoliation missions in Vietnam as recorded on HERBS tape.


Herbicide defoliation missions in Vietnam as recorded on HERBS tape. SOURCE: NAS, 1974. NOTE: Lines indicate mission tracks.

FIGURE 3-2b. Herbicide defoliation missions in Vietnam during 1966.


Herbicide defoliation missions in Vietnam during 1966. SOURCE: NAS, 1974. NOTE: Lines indicate mission tracks.

FIGURE 3-2c. Herbicide defoliation missions in Vietnam during 1967.


Herbicide defoliation missions in Vietnam during 1967. SOURCE: NAS, 1974. NOTE: Lines indicate mission tracks. Shading indicates populated area.

FIGURE 3-2d. Herbicide defoliation missions in Vietnam during 1968.


Herbicide defoliation missions in Vietnam during 1968. SOURCE: NAS, 1974. NOTE: Lines indicate mission tracks.

FIGURE 3-2e. Herbicide defoliation missions in Vietnam during 1969.


Herbicide defoliation missions in Vietnam during 1969. SOURCE: NAS, 1974. NOTE: Lines indicate mission tracks.

Another heavily sprayed area, the Ca Mau Peninsula at the southern tip of South Vietnam, was almost entirely covered with dense mangrove forests up to 1968. However after extensive spraying of the peninsula in 1967 and 1968, the NAS (1974) concluded that nearly half of the mangrove trees had been destroyed. Mangrove forests were more heavily affected by herbicide spraying than any other vegetation type in South Vietnam. One spray usually killed all mangrove trees (NAS, 1974).

Another limitation of the HERBS tapes, and the maps generated from it, is that the plotted lines represent the center of each mission. The assumed swath width for a sortie was 80 m. Typical missions consisted of three aircraft, and some as many as 12 to 16; these differences in effective spray area are not reflected by the maps. A detailed study of the frequency of sprays in the Rung Sat Special Zone conducted by the NAS (1974) is shown in Figure 3-3.

FIGURE 3-3. Herbicide spray missions (1966-1967) in the Rung Sat Special Zone.


Herbicide spray missions (1966-1967) in the Rung Sat Special Zone. Data from HERBS tape include date of mission, number of gallons, and type of herbicide agent. SOURCE: NAS, 1974.

For each herbicide mission, the date, number of gallons sprayed, and type of herbicide are indicated. These maps show how many times any hectare had been sprayed due to repetition or overlapping of herbicide applications and, more accurately, depict the extent of spraying conducted in the Rung Sat Special Zone during 1966 and 1967. Areas designated as defoliation targets were much more likely to be sprayed repeatedly than targets of crop destruction missions. Less than 10 percent of the targets for crop destruction missions were sprayed more than once, and the intervals were usually 6 to 12 months; one-third of the areas classified as defoliation were resprayed, and approximately 70 percent received the second spray within 6 months of the initial spray (NAS, 1974).

Military documents report the use of herbicides over areas of Laos, particularly near the Vietnam border and along the Ho Chi Minh Trail. The purpose of the operation in Laos was to expose foot trails, roads, and other lines of communication that led into Vietnam. Herbicide operations began in December 1965; within a six month period, more than 200,000 gallons of herbicide had been sprayed over approximately 1,500 km of roads and trails in Laos (Collins, 1967).


Some 3 million U.S. military personnel served in or near Vietnam, but the precise number cannot be readily determined from existing military records since individual service records have not been computerized. Surveys of veterans vary in their estimates because of differences in terminology and sample selection procedures. Existing military records do document assignments of military personnel to units and the location of most units at most times. Individual military experiences of Americans who served in Vietnam varied as the nature of the war in different areas of the country changed over time. Individual experiences also varied by branch of service, military occupation, rank, and type of military unit.

Between 1962 and 1971, U.S. military forces sprayed nearly 19 million gallons of herbicides over approximately 3.6 million acres in South Vietnam. The preparation known as Agent Orange accounted for approximately 11.2 million gallons of the total amount sprayed. Seven different herbicide formulations were used in varying quantities for a variety of purposes in different parts of the country. Approximately 65 percent of all herbicides sprayed were contaminated by TCDD, in varying concentrations. Herbicides were used to strip the thick jungle canopy that helped conceal opposition forces, to destroy crops that enemy forces might depend upon, and to clear tall grass and bushes from around the perimeters of U.S. base camps and outlying fire support bases.

Aerial spraying of herbicides by Operation Ranch Hand accounted for approximately 86 percent of all spraying, and existing computerized records indicate which herbicides were used and where. These records indicate that the spraying was not uniform, but concentrated in certain geographical and tactical areas. Units and individuals other than the members of the Air Force Ranch Hand, such as the Army Chemical Corps, were also likely to have handled or sprayed herbicides around bases or lines of communication. Considerable quantities of herbicides were also sprayed from boats and ground vehicles, as well as by soldiers wearing back-mounted equipment. Although the recording of such sprays was not as systematic as those of Ranch Hand, some records do exist on the ''Services HERBS" computer tape.


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Copyright 1994 by the National Academy of Sciences. All rights reserved.
Bookshelf ID: NBK236347


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