Operation Popeye (Project Popeye/Motorpool/Intermediary-Compatriot) was a highly classified weather modification program in Southeast Asia during 1967-1972. The cloud seeding operation during the Vietnam war ran from March 20, 1967 until July 5, 1972 in an attempt to extend the monsoon season, specifically over areas of the Ho Chi Minh Trail. The operation was used to induce rain and extend the East Asian Monsoon season in support of U.S. government efforts related to the War in Southeast Asia.
The operation seeded clouds with both silver iodide and lead iodide, resulting in the targeted areas seeing an extension of the monsoon period by an average of 30 to 45 days. As the continuous rainfall slowed down the truck traffic, it was considered relatively successful. However, 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.
The former U.S. Secretary of Defense, Robert S. McNamara, 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.
The chemical weather modification program was conducted from Thailand over Cambodia, Laos, and Vietnam and allegedly sponsored by Secretary of State Henry Kissingerand CIA without the authorization of then Secretary of Defense Melvin Laird who had categorically denied to Congress that a program for modification of the weather for use as a tactical weapon even existed.