Comment: It has been used for warfare since at least Vietnam, 1967

Under the auspices of the Air Weather Service, the United States' Operation Popeye used cloud seeding over the Ho Chi Minh Trail, increasing rainfall by an estimated thirty percent during 1967 and 1968. It was hoped that the increased rainfall would reduce the rate of infiltration down the trail.

https://en.wikipedia.org/wiki/Weather_warfare