In addition to providing underground shelter, the Cu Chi tunnels served a key role during combat operations, including as a base for Communist attacks against nearby Saigon. VC soldiers lurking in the tunnels set numerous booby traps for U.S. and South Vietnamese infantrymen, planting trip wires that would set off grenades or overturn boxes of scorpions or poisonous snakes onto the heads of enemy troops. To combat these guerrilla tactics, U.S. forces would eventually train some soldiers to function as so-called “tunnel rats.” These soldiers (usually of small stature) would spend hours navigating the cramped, dark tunnels to detect booby traps and scout for enemy troops.
In January 1966, some 8,000 U.S. and Australian troops attempted to sweep the Cu Chi district in a large-scale program of attacks dubbed Operation Crimp. After B-52 bombers dropped a large amount of explosives onto the jungle region, the troops searched the area for enemy activity but were largely unsuccessful, as most Communist forces had disappeared into the network of underground tunnels. A year later, around 30,000 American troops launched Operation Cedar Falls, attacking the Communist stronghold of Binh Duong province north of Saigon near the Cambodian border (an area known as the Iron Triangle) after hearing reports of a network of enemy tunnels there. After bombing attacks and the defoliation of rice fields and surrounding jungle areas with powerful herbicides, U.S. tanks and bulldozers moved in to sweep the tunnels, driving out several thousand residents, many of them civilian refugees. North Vietnamese and VC troops slipped back within months of the sweep, and in early 1968 they would use the tunnels as a stronghold in their assault against Saigon during the Tet Offensive.