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Hidden History of the US: When the Weather Was a Weapon

Kristine has a B.A. in Journalism from Penn State University and an M.A. in Liberal Studies from the University of Michigan.

Cloud seeding as done from an airplane

Cloud seeding as done from an airplane

When Weather Became a Weapon of War

Most of us are familiar with efforts to harness certain aspects of nature to use as weapons of destruction—such as using the element hydrogen to make the hydrogen bomb. Very few, however, are aware that the United States once attempted to use the weather as a weapon of war.

Seymour Hersh's 1972 Article

In July of 1972, Pulitzer Prize-winning reporter Seymour Hersh wrote an article for The New York Times titled “Rainmaking Is Used As Weapon by U.S.” describing how the U.S. military had been seeding clouds in Asia—namely over Vietnam and Laos—in an effort to control rainfall. The military was attempting to increase the amount of rain falling in these areas to inhibit the movement of North Vietnamese troops and equipment, as well as to deter the use of anti-aircraft missile fire.

The article confirmed widely-circulated rumors in both the halls of Congress and in the scientific community regarding attempts at weather modification in Southeast Asia. The experiments were first tried in South Vietnam in 1963. Hersh’s report stated that although meteorological warfare is not prohibited by international laws, some State Department officials had expressed concern over both the long-term effects of such manipulation, as well as the ethical implications of the experiments.

Advocates of the program, however, believe that weather modification could potentially save lives. One military official was quoted in Hersh’s article as saying “What’s worse, dropping bombs or rain?”

Operation Popeye in Vietnam

According to The New York Times article, the White House and the State Department at the time declined to comment on the experimental cloud seeding. But officials who spoke with Hersh agreed that the cloud seeding had accomplished its main objectives of muddying the Ho Chi Min Trail and disrupting lines of communication. Officials denied, however, that the project had dramatically altered the climate or landscape, nor did the seeding have the ability to cause catastrophic flooding in North Vietnam.

The experimental program did not catch the attention of Congress until 1974. The Senate Committee on Foreign Relations was briefed that year on the top-secret five-year program dubbed Operation Popeye, according to the March 20, 2018 article titled “With Operation Popeye, the U.S. Government Made Weather An Instrument of War” in Popular Science magazine.

The program went through several names in its history before the term “Operation Popeye” stuck. According to the Office of the Historian on the State Department website,, a memorandum from Deputy Undersecretary of State for Political Affairs Foy David Kohler to Secretary of State Dean Rusk in January of 1967 stated that the test phase of what was then called Project Popeye was approved by the State and Defense departments in 1966. The cloud-seeding experiment was then tried on a strip of land in the Laos panhandle in the valley region of the Se Kong River. The test was conducted without the consent of Laotian authorities.

At the point the U.S. military initiated Operation Popeye, the Vietnam War had been ongoing for the past decade and had already cost 8,000 American lives. With conventional warfare making little headway, American officials began looking for alternative ways to turn the tide of the war, according to the Popular Science article.

More than 50 cloud-seeding experiments were conducted during the test phase, and according to the State Department memo, were deemed successful by the Department of Defense.

Cloud Seeding

Cloud seeding is a method of artificially creating precipitation such as rain or snow. According to Popular Science, the practice originated in 1946 when a General Electric employee named Vincent Schaefer, a self-taught chemist, was experimenting with dry ice. Schaefer discovered that the particles around which water condenses—called cloud condensation nuclei—could be used to artificially create rain or snow and tested his hypothesis by “seeding” clouds over the Berkshire Mountains in Massachusetts. His experiment worked and the process of “cloud seeding” was created.

His discovery, however, was not without controversy. Some scientists hailed it as a method for eliminating droughts. Others, however, expressed concern that rain would essentially be “stolen” from some areas by pulling precipitation out of the clouds meant for one location in favor of watering a more “desirable” locale.

The memorandum to Secretary of State Rusk reported that during the test phase, 82 percent of the clouds seeded successfully produced rain at higher than normal levels. That amount of rainfall successfully inhibited motor vehicles as well as prohibited the Viet Cong from making repairs to the road. The report indicated that “DOD scientists consider that the experiment demonstrated a capacity to raise and maintain rainfall under controlled conditions to the level at which the land is saturated over a sustained period, slowing movement on foot and rendering the operation of vehicles impracticable.”

When reports that the U.S. military was attempting to alter the weather in Indochina began to leak, the Nixon administration stringently denied the project existed, according to Popular Science. When the Pentagon Papers were leaked in 1971, they confirmed the existence of Operation Popeye.

According to Popular Science magazine, "The close monitoring of troop and truck traffic along routes where rain had fallen verified beyond any doubt the naturally adverse effects of rainfall and accumulated soil moisture on the enemy's logistic effort," Lieutenant Colonel Ed Soyster, a member of the Operation Popeye team, told the Senate Committee on Foreign Relations, as stated in declassified notes from a 1974 meeting. The purpose of Operation Popeye was to damage roads, render rivers impassable, and extend the time period when portions of Vietnam were unreachable, according to Soyster.

Ultimately, the project would span five years and cost taxpayers an estimated $15 million. Initially, Operation Popeye concentrated on the Ho Chi Min Trail from Cambodia to Laos, but would eventually expand to include North Vietnam. Between 1967 and 1972, 2,602 flights were made to disperse 47,409 cloud seeding cartridges, according to the article “Operation Popeye: America’s Secret Weather Warfare Project” on the website.

After the hearings conducted by the Senate Foreign Relations Committee, a report on the project to the U.S. Congress questioned the success of the program and stated that its effectiveness was unverified. The project was scrapped since the results could not be positively confirmed. However, some historians believe that while the program was being conducted, the area around the Ho Chi Min Trail received an extra 35 inches of rain, according to the article.

When the experimental program became public knowledge, scientists speculated whether or not Operation Popeye had deprived neighboring countries such as Thailand of necessary rainwater by diverting it elsewhere, citing a decrease in precipitation in Thailand during the period Operation Popeye was in effect. In 1977, the United Nations held a summit on the ethical and environmental impacts of weather warfare. As a result of this summit, the U.N. passed the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques resolution in May of 1977, outlawing the use of weather modification experiments and programs by military forces.

That does not mean, however, that weather modification has been completely outlawed. According to, the United Arab Emirates regularly uses cloud seeding to increase rainfall in their country by as much as 35 percent annually. In 2008, the Chinese government used cloud seeding after a short drought to increase snowfall while preparing to host the Winter Olympics. Although no longer used as a weapon of war, cloud seeding is used to enhance rain and snowfall all over the world, thanks in part to the United States’ efforts to turn the tide of a military conflict.


This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.