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American soldiers used the term "Black Echo" to describe the conditions within the tunnels. In both sites low-power lights have been installed in the tunnels to make traveling through them easier, and both sites have displays of the different types of booby traps that were used. This approach proved ineffective due to the design of the tunnels and the strategic use of trap doors and air filtration systems. However the Australians pressed on and revealed, for the first time, the immense military significance of the tunnels. Strategic Hamlet Program Please help improve this article by adding citations to reliable sources. Retrieved from " https: The tunnels were used by Viet Cong soldiers as hiding spots during combat, as well as serving as communication and supply routes, hospitals, food and weapon caches and living quarters for numerous North Vietnamese fighters. These specialists, commonly known as " tunnel rats ", would enter a tunnel by themselves and travel inch-by-inch cautiously looking ahead for booby traps or cornered PLAF.