From duck.ai:

Project Cirrus, 1947–1948: The U.S. military and General Electric attempted to weaken or redirect hurricanes by seeding them. One storm, Hurricane King, was seeded in 1947. It later changed direction and hit Savannah, Georgia, leading to public controversy and lawsuits, although scientists could not establish that the seeding caused the change. The project was eventually abandoned.

Operation Popeye, 1967–1972: During the Vietnam War, the United States secretly seeded clouds over parts of Vietnam, Laos, and Cambodia to extend the monsoon season and make roads harder to use. Aircraft dispersed silver iodide into clouds in an effort to increase rainfall. The operation became public through congressional investigations and press reports.

Other Cold War programs: The United States, the Soviet Union, and other countries investigated cloud seeding for rainmaking, hail suppression, fog dispersal, and snowpack enhancement. Some military interest focused on obscuring visibility, improving or disrupting transportation, or influencing battlefield conditions. Most results were inconsistent because cloud behavior is difficult to control and experiments are hard to separate from natural weather variation.

International restrictions: In response to concerns about environmental warfare, the United Nations adopted the Environmental Modification Convention (ENMOD) in 1977. It prohibits hostile military or other uses of environmental modification techniques that have widespread, long-lasting, or severe effects. It does not ban peaceful weather-modification research.