Operation Popeye
Project Popeye

Weather modification was a technology once embraced by the US military as a tool to help both wartime and peacetime missions. However, interest in the ability to modify weather waned following the end of the conflict in Vietnam and became virtually non-existent after the passage of the Environmental Modification (ENMOD) Treaty in 1977, which prohibited offensive weather modification from occurring over a large area.
With the onset of conflict in Southeast Asia, operational interest in modifying weather to support combat operations increased. The goal of such a program would be to flood supply routes used by the North Vietnamese into South Vietnam by seeding clouds in the area. Between 1949 and 1978 China Lake developed concepts, techniques, and hardware that were successfully used in hurricane abatement, fog control, and drought relief.
The use of weather modification as a tool of warfare was very much a by-product of developments to use weather modification techniques for peacetime missions. One method that was tried, but later abandoned by the military was the use of aircraft dry ice seeding to dissipate cold fog. In the late 1960s and early 1970s, specially configured WC-130 aircraft were equipped with a dry ice crusher and dispenser. On a typical mission such aircraft would fly a seeding pattern consisting of between 5 and 30 parallel lines, each 5-6 miles long and 0.5 to 1.5 miles apart. This pattern would be flown just above the fog at a distance between 45 and 60 minutes upwind of the area where clearing was desired, with the machine generally dispensing 15 pounds of crushed dry ice per minute. The hole then, would hopefully drift over the desired area at the desired time. The return on the investment in these operations was significant. During the winter of 1969-70 for instance, fog dispersal operations in the United States via this method cost $80,000 but saved $900,000. As weather modification became discredited in the mid-1970s, however, this method was abandoned.
A weather modification program for selected areas of Laos, which subsequently known as Project Popeye (also referred to as Operation Popeye), was proposed by the Joint Chiefs of Staff on 10 August 1966. The Command of US Military Assistance Command, Vietnam (COMUSMACV) and the Commander in Chief of US Pacific Command (CINCPAC) concurred in the proposal and recommended that it be carried out in selected areas of the Tiger Hound area of operation in Laos. The Joint Chiefs of Staff granted approval on 1 September 1966 and the execute order was issued on 17 September 1966.
The Joint Chiefs of Staff approved the project to extend the rainy season by cloud seeding in Laos, as a means of denying the enemy vehicular lines of communication. According to in