Vietnam War
The communists were supplied by a vast network of hidden trails, known as the Ho Chi Minh Trail. It was very well hidden although many attempts were made by the US to bomb and destroy it. Supplies and soldiers from North Vietnam were sent through Laos to communists forces in South Vietnam. American planes heavily bombed the Ho Chi Minh Trail, and  of bombs were dropped on Laos. That slowed down but did not stop the trail system.