American fighter bombers fly over across South Vietnam, Laos and Cambodia dropping bombs filled with tiny fiberglass shards.

A few hours later, Viet Cong insurgents — and anyone else unfortunate enough to move into the contaminated areas — begin to develop maddening itches and painful sores. Some go blind from glass in their eyes.

This was the horrifying plan researchers at defense contractor HRB Singer developed for the Office of Naval Research in 1967. Part of a larger program nicknamed Project Poorboy during the Vietnam War, the Pentagon funded research into methods for stopping insurgents from moving down the Ho Chi Minh Trail.

“The technique and substance recommended are not absolute,” the scientists explained in a 1968 review of the project. “[But] they do provide a means of identifying trespassers, of causing irritation and incapacitation as time progresses without engendering cries of bacteriological or chemical warfare.”

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Image courtesy of U.S. Navy