Iron Triangle (War Zone D)

The Iron Triangle was a National Liberation Front (NLF) stronghold 20 miles northwest of Saigon, which had been built by the Vietminh twenty years before in the war against French colonialism. Serving as a supply depot and staging area with an immense underground complex including command headquarters, dining halls, hospital rooms, munitions factories, and living quarters, it was never cleared by the French, nor was it successfully neutralized by the United States or ARVN, Army of the Republic of Vietnam. Located between Saigon, Tay Ninh, and Song Be cities, the Triangle comprised about 125 square miles and included portions of Bien Hoa, Binh Duong, Phuoc Long, Long Khanh, and Hau Nghia provinces. It was by and large bounded by the Saigon River, the Song (river) Thi Thinh north of Bien Hoa, and the Than Dien Forest in Binh Duong Province. The area was thickly forested, consisting of jungle and rubber plantations and containing a few small villages and hamlets, the most strategic being Ben Suc, which had been under NLF control since 1964.

In January 1967, the United States and ARVN mounted the war's first major combined operation and the first U.S. corps-size operation. Operation Cedar Falls deployed 32,000 troops against the Triangle. Its "search and destroy" objective was to engage and eliminate enemy forces, destroy base camps and supplies, remove all noncombatants along with possessions and livestock to strategic hamlets, and completely destroy four principal villages. Vast underground complexes were found, and large quantities of supplies and papers were captured. The complete U.S. arsenal was employed—intensive bombing, flamethrowers, chemical warfare (defoliants and the first authorized major use of CS, or tear gas), and land-clearing Rome plows. Units participating in Cedar Falls included the 173rd Airborne Brigade, the 196th and 199th Infantry brigades, elements of the 1st and 25th Infantry divisions, the 11th Armored Cavalry Regiment, and the ARVN 5th Ranger Group.

There was little fighting as the NLF fled to sanctuaries in Cambodia until the operation was finished. However, the destruction, chronicled in Jonathan Schell's The Village of Ben Suc, was considerable. About 7,000 refugees were created and the region was made uninhabitable to anyone other than NLF-NVA forces. The operation's magnitude increased NLF utilization of Cambodian sanctuaries; however, they did return to rebuild camps which became springboards for the assault on Saigon during the Tet Offensive, 1968. Ensuing operations against the Iron Triangle included Uniontown, Atlas Wedge, and Toan Thang.