The U.S. also engaged in weather modification through Project Popeye, a secret program from 1967 to 1972 that seeded clouds with silver iodide to prolong the monsoon season in an attempt to cut the flow of fighters and supplies coming down the Ho Chi Minh Trail from North Vietnam. Congress eventually passed a bipartisan resolution in 1973 urging an international treaty to prohibit the use of weather modification as a weapon of war. That treaty came into effect in 1978.

The U.S. military contended that all these tactics were operationally successful as a trade of trees for American lives.

Despite Congress’ concerns, there was little scrutiny of the environmental impacts of U.S. military operations and technologies. Research sites were hard to access, and there was no regular environmental monitoring.