Operation Popeye (Project Popeye/Motorpool/Intermediary-Compatriot) was a US military cloud seeding operation (running from March 20, 1967 until July 5, 1972) during the Vietnam war to extend the monsoon season over Laos, specifically areas of the Ho Chi Minh Trail. The operation seeded clouds with silver iodide, resulting in the targeted areas seeing an extension of the monsoon period an average of 30 to 45 days. As the continuous rainfall slowed down the truck traffic, it was considered relatively successful. The 54th Weather Reconnaissance Squadron carried out the operation to "make mud, not war." 
The resultant rain and subsequent flooding of the nearby Song Con River is sometimes blamed for the move of POWs from the prison camp at Son Tay and therefore, the failure of Operation Ivory Coast.
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Project Popeye was an experiment in increased rainfall through cloud seeding jointly approved by the U.S. Department of State and U.S. Department of Defense. The technical aspects of the experiment were verified by Dr. Donald F. Hornig, Special Assistant to the President of the United States for Science and Technology. The government of Laos was not informed of the project, its methods or its goals.
Robert S. McNamara, U.S. Secretary of Defense, was aware that there might be objections raised by the international scientific community but said in a memo to the president that such objections had not in the past been a basis for prevention of military activities considered to be in the interests of U.S. national security.
During October 1966, Project Popeye was tested in a strip of the Laos panhandle east of the Bolovens Plateau in the Se Kong River valley. The test was conducted by personnel from the Naval Ordnance Test Station located at China Lake California. Fifty cloud seeding experiments were conducted with the result that 82% of the clouds produced rain within a brief period after having been seeded. It was claimed that one of the clouds drifted across the Vietnam border and dropped nine inches of rain on a US special forces camp over a four hour period. After the successful completion of the test phase, Project Popeye transitioned from an experiment to an operational program of the U.S. Defense department.
Operation Popeye goal was to increase rainfall in carefully selected areas to deny the Vietnamese enemy, namely military supply trucks, the use of roads by:
- Softening road surfaces
- Causing landslides along roadways
- Washing out river crossings
- Maintain saturated soil conditions beyond the normal time span.
Starting on March 20, 1967, and continuing through every rainy season (March to November) in Southeast Asia until 1972, operational cloud seeding missions were flown. Three C-130 Hercules aircraft and two F-4C Phantom aircraft based at Udorn Royal Thai Air Force Base Thailand flew two sorties per day. The aircraft were officially on weather reconnaissance missions and the aircraft crews as part of their normal duty generated weather report information. The crews, all from the 54th Weather Reconnaissance Squadron, were rotated into the operation on a regular basis from Guam. Inside the squadron, the rainmaking operations were code-named "Motorpool".
The initial area of operations was the eastern half of the Laotian panhandle. On 11 July 1967, the operational area was increased northward to around the area of the 20th parallel and included portions of far western North Vietnam. In September 1967, the A Shau Valley in South Vietnam was added to the operational area. Operations over North Vietnam were eliminated on April 1, 1968, concurrent with conventional bombing restrictions being put into effect. The southern region of North Vietnam was added to the operational area on September 25, 1968, and then removed on November 1st of that year concurrent with a halt to conventional bombing of North Vietnam. In 1972, most of northeastern Cambodia was added to the operational area.
All rainmaking operations ceased on July 5, 1972.
Reporter Jack Anderson published a story in March 1971 concerning Operation Popeye (though in his column, it was called Intermediary-Compatriot). The name Operation Popeye (Pop Eye) entered the public space through a brief mention in the Pentagon Papers and a July 3, 1972, article in the New York Times. Operations in Laos ceased two days after the publication of the Times article.
The press stories led to demands from members of the U.S. Congress, led by Senator Claiborne Pell, for more information. U.S. House and Senate resolutions in favor of banning environmental warfare were passed as Senate Resolution 71 on July 11, 1973, H.R. 116 of 1974, H.R. 329 of 1974 and H.R. 28 of 1975.
Current legal status
Weather modification procedures when performed to achieve a military end now fall under the provenance of the Environmental Modification Convention.
- Weather Modification Hearing, United States Senate Subcommittee on Oceans and International Environment of the Committee on Foreign Relations, March 20, 1974
Published government documents
- Keefer, Edward C. Foreign Relations of the United States 1964-1968 Volume XXVII Laos United States Government Printing Office, 1998.
- "Laos, 1948-1989; Part 2". Acig.org. Retrieved 2009-07-25.
- Will Thomas Author. "Weather Warfare/Global Dominance Over Weather/Full Spectrum Dominance By Us Over Weather". Willthomas.net. Retrieved 2009-07-25.
- "ENMOD and the US Congress". Sunshine-project.org. Retrieved 2009-07-25.
- "The Pentagon Papers, Gravel Edition, Volume 4, Chapter 2, "US Ground Strategy and Force Deployments, 1965-1968, pp. 277-604, 3rd section". Mtholyoke.edu. Retrieved 2009-07-25.
- Hersh, Seymour M. (July 3, 1972). "Rainmaking Is Used As Weapon by U.S.; Cloud-Seeding in Indochina Is Sa... - Free Preview - The New York Times". Select.nytimes.com. Retrieved 2009-07-25.
- Transcript of the US Senate Hearing on Weather Modification of March 20, 1974
- Operation Motorpool Gallery
- Dr. Edwin X Berry's 1969 trip to Philippines for Operation Popeye (Berry now at www.climatephysics.com)