The tunnels of Củ Chi are an immense network of connecting underground tunnels located in the Củ Chi District of Ho Chi Minh City (Saigon), Vietnam, and are part of a much larger network of tunnels that underlie much of the country. The Củ Chi tunnels were the location of several military campaigns during the Vietnam War, and were the Viet Cong's base of operations for the Tết Offensive in 1968.
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. The tunnel systems were of great importance to the Viet Cong in their resistance to American forces, and helped to counter the growing American military effort.
American soldiers used the term "Black Echo" to describe the conditions within the tunnels. For the Viet Cong, life in the tunnels was difficult. Air, food and water were scarce and the tunnels were infested with ants, poisonous centipedes, scorpions, spiders and vermin. Most of the time, soldiers would spend the day in the tunnels working or resting and come out only at night to scavenge for supplies, tend their crops, or engage the enemy in battle. Sometimes, during periods of heavy bombing or American troop movement, they would be forced to remain underground for many days at a time. Sickness was rampant among the people living in the tunnels, especially malaria, which was the second largest cause of death next to battle wounds. A captured Viet Cong report suggests that at any given time half of a PLAF unit had malaria and that “one-hundred percent had intestinal parasites of significance".