Tunnels Of Củ Chi, Ho Chi Minh City, Saigon, Vietnam

On January 18, tunnel rats from the 1st BN 5th Infantry Regiment, of the 25th Infantry Division, accomplished the uncovering of the Viet Cong district headquarters of Củ Chi containing half a million documents concerning all types of military strategy. Among the documents were maps of U.S. bases, detailed accounts of PLAF movement from Cambodia into Vietnam, lists of political sympathizers, and even plans for a failed assassination attempt on Robert McNamara.
By 1969, B-52s were freed from bombing North Vietnam and started "carpet bombing" Củ Chi and the rest of the Iron Triangle. Ultimately it proved successful. Towards the end of the war, the tunnels were so heavily bombed that some portions actually caved in and other sections were exposed. But by that time, they had succeeded in protecting the local North Vietnamese units in "surviving to fight another day".
Throughout the course of the war, the tunnels in and around Củ Chi proved to be a source of frustration for the U.S. military in Saigon. The Viet Cong had been so well entrenched in the area by 1965 that they were in the unique position of locally being able to control where and when battles would take place. By helping to covertly move supplies and house troops, the tunnels of Củ Chi allowed North Vietnamese fighters in their area of South Vietnam to survive, help prolong the war and increase American costs and casualties until their eventual withdrawal in 1972, and the final defeat of the Republic of Vietnam in 1975.