Overview of "weather warfare" history.

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Apparent early successes with cloud-seeding tactics that induced rain spurred the Pentagon to fund modest efforts for some 20 years, and it unleashed a concerted five-year assault during the Vietnam War, starting in 1967. Dubbed Project Popeye, its goal was to prolong the monsoon season and thus impede the movement of enemy troops and supplies on muddy jungle trails.

By 1977, the military was spending $2.8 million a year on weather-modification research. That year, partly in reaction to Popeye, the United Nations passed a resolution banning the hostile use of all environmental modification techniques. This led to a treaty that the U.S. ratified in 1978. Although the treaty doesn't ban peaceful applications, or so-called benign weather modification, the Pentagon elected to eliminate all such research in 1979. The Kremlin continued its weather-modification work, however.

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