Iron Triangle ( Vietnam ) The Iron Triangle ( Vietnamese : " Tam Giác Sắt " ) was a area in the Binh Duong Province of Vietnam , so named due to it being a stronghold of Viet Minh activity during the war . The region was under control of the Viet Minh throughout the French war in Vietnam and continued to be so throughout the phase of American involvement in the Vietnam War , despite concerted efforts on the part of US and South Vietnamese forces to destabilize the region as a power base for their enemy , the communist North Vietnamese - sponsored and - directed South Vietnamese insurgent movement , the National Liberation Front or Viet Cong ( NLF ) . Geography . The Location of the Iron Triangle was between the Saigon River on the west and the Tinh River on the east and bordering Route 13 about 25 miles ( 40 km ) north of Saigon . The southern apex of the " triangle " was seven miles ( 11 km ) from Phu Cong , the capital of Binh Duong Province . Its proximity to Saigon was both a reason for American and South Vietnamese efforts to eradicate it , as well as why it remained a crucial area for Communist forces to maintain control over . History . The French War . During the French war in Indochina , from 1946 – 1954 , the Vietminh elaborated on a network of hidden fortifications and tunnels throughout the region to defend themselves against the superior military power of the French . These tunnel networks had begun as early as the 1880s to resist French occupation . The network afforded communist fighters the ability to " disappear " into the countryside . This became especially important during the Vichy Regime , when Vietnam was dually occupied by French and Japanese forces , so as to remain undetected by not one but two occupying enemies . The American War . The tunnels were expanded further after the war with the French as a base for underground operations against the Ngo Dinh Diem government and later US - backed South Vietnamese governments . The tunnel system at its height was said to have over of tunnels throughout North and South Vietnam , with hundreds of miles of these located in the Iron Triangle , especially concentrated in the area around the town of Cu Chi . Due to the threat that the Cu Chi tunnels posed to the Saigon Government , the United States stepped up its military offensive in the region in the fall of 1966 and 1967 . They launched three operations during this time : Operation Attleboro , Operation Cedar Falls and Operation Junction City . Operation Cedar Falls was an especially intensive attack involving nearly 16 , 000 American troops and 14 , 000 soldiers of the South Vietnamese Army . The Operation took nineteen days and 72 Americans and 720 Viet Cong were killed . Despite their massive attack with B - 52 bombers and Rome plows and efforts to destroy the tunnel system with explosives , flooding , and " tunnel rats " ( specially trained soldiers who would infiltrate the tunnels armed only with a flashlight and a handgun ) , the Americans failed to totally destroy the Viet Cong support system that had been built for over two decades . The Iron Triangle at the end of the Vietnam War . The area remained an active organizing center for the Viet Cong right through to the end of the war , due to both its undeniable strategic importance , as well as support from local populations who had been negatively impacted by the American bombing campaign . In April , 1975 , General Van Tien Dung , political bureau members Pham Hung and Le Duc Tho and southern military commander Tran Van Tra all joined together in the Iron Triangle region to orchestrate the final , decisive attack on Saigon . The area had remained allied with the nationalist communist forces from the beginning of the French war in 1946 to the fall of Saigon in 1975 : an exception in a country often torn region by region between control by American forces and control by the Viet Cong .