IN VIETNAM
Operation POPEYE was a military cloud-seeding project carried out by the U.S. Air Force during the Vietnam War in 1967–1972. The highly classified program attempted to extend the monsoon season over specific areas of the Ho Chi Minh Trail, in order to disrupt North Vietnamese military supplies by softening road surfaces and causing landslides. 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 Udon Thani Royal Thai Air Force Base in Thailand flew two sorties per day. Operation POPEYE's goal was to increase rainfall in carefully selected areas to deny the Vietnamese enemy, namely military supply trucks, the use of roads by:
1. Softening road surfaces
2. Causing landslides along roadways
3. Washing out river crossings
4. Maintaining saturated soil conditions beyond the normal time span.