When the U.S. Navy blockaded the coastline of South Vietnam, the North Vietnamese sent their supplies overland through Laos and Cambodia by turning 12,000 miles of jungle footpaths into roadways. Dubbed the "Ho Chi Minh Trail," the American military reasoned that if it could be sufficiently damaged, the enemy would be unable to sustain itself. Three million tons of explosives would be dropped on the Laos portion of the trail alone. But as often as the Trail was bombed, it was repaired. As many as 230,000 North Vietnamese teenagers—many of them volunteers and over half of them women—worked to keep the roads open.

NOTE: This video is part of a lesson plan titled Trying to Find the Right Formula.