The Saigon River makes its way from Cambodia southeast to Saigon, then continues on towards the South China Sea — its final destination. As the river approaches Saigon (now Ho Chi Minh City), the Cu Chi district sits on its right bank and an area that was called by U.S. military men the Iron Triangle is on its left bank. In January 1967, this region became the scene of the largest U.S. ground operation of the Vietnam War: Operation Cedar Falls.

An Ominous Threat From a Viet Cong Stronghold

Only twenty kilometers from Saigon, the Iron Triangle was the closest Communist haven to South Vietnam’s capital city. It had even been characterized as a “dagger pointed at Saigon”. The area was heavily fortified and known to contain the headquarters for the Viet Cong’s Military Region IV, which served to direct military, political and terrorist activities in the greater Saigon region. Control of the Iron Triangle positioned the Viet Cong to dominate key transportation routes in the surrounding area. With American troop deployments in Vietnam approaching their peak level, U.S. commanders decided that this important center for enemy operations control and support had to be attacked decisively and in force.

Operation Cedar Falls would kick off on January 8, 1967. II Field Force, Vietnam would attack the Iron Triangle and the Thanh Dien Forestry Reserve to its north. The mission was to destroy all enemy forces, infrastructure and the Military Region IV headquarters; to evacuate the civilian population and establish the Iron Triangle as a specified strike zone to preclude its further use as a support base for Viet Cong operations.

The Cu Chi Tunnel Network

Cu Chi Tunnels Cu Chi, June 5 - 6, 1966: A U.S. Army soldier is lowered head-first into a Viet Cong tunnel, to see what's inside. Then, the entrance area of the tunnel is destroyed.

In their war against the French, the Viet Minh had elaborated on an old network of tunnels and hidden fortifications throughout the region. Following the departure of the French, the tunnel system was expanded into an immense network serving as a base for underground operations against the South Vietnamese government. The tunnel system contained makeshift hospitals, training grounds, storage facilities, military headquarters and more. Viet Cong guerrillas might stay underground for several months at a time.

Hundreds of miles of tunnels were located in the Iron Triangle region, with a special concentration around the town of Cu Chi. Nearby was a former French owned rubber plantation called Ho Bo Woods. The Viet Cong had built an extensive bunker and tunnel network there — in some places the tunnels were three or four levels deep!

A Hammer and Anvil That Smashed Thin Air

Virtually since the beginning of the Vietnam War, the Iron Triangle had been used as a major communist staging ground and rear area which, by 1966, South Vietnamese government officials and military forces dared not enter. General Westmoreland had formulated plans to go on the offensive, driving People's Army of Vietnam and Viet Cong forces out of South Vietnam's densely populated coastal regions and pushing them northwest into the lightly populated border region. There, U.S. forces could take advantage of their superior firepower.

The operation would employ an entrapment maneuver called "hammer and anvil". Numerous attempts at implementing this tactic were made during the years of heaviest U.S. involvement in Vietnam, with consistently disappointing results. In the first stage, blocking positions, or the "anvil", were stealthily positioned along the Saigon River, which formed the southwestern leg of the triangle. In the second stage, armored cavalry and airborne infantry moved as "hammers", sweeping across the triangle from the east and from the north. It was to be an "Iron Triangle" in more ways than one.

As it turned out, the massive assault largely encountered air — the Viet Cong evaded their attackers by either fleeing to Cambodia or by hiding in the complex underground tunnel network. The largest ground operation of the Vietnam War was characterized by small unit actions and not by large scale combat.

Tunnel Rats: Specialists in a New Type of Warfare

Operation Cedar Falls saw the introduction of tunnel rats, an elite group of volunteers specializing in the art of tunnel warfare. Armed only with a pistol, a knife, a flashlight and a piece of string, these specialists would enter a tunnel alone and cautiously advance inch-by-inch, watching for booby traps or Viet Cong lying in wait. Although American ground forces failed to locate and destroy significant assemblies of enemy forces, the tunnel rats did uncover parts of the secret tunnel system and uncovered the Viet Cong district headquarters at Cu Chi. There they discovered half a million military documents, among which were documents on strategy, maps of U.S. bases, accounts of guerrilla force movements from Cambodia into Vietnam, and lists of South Vietnamese political sympathizers. After being searched to the extent possible, tunnel complexes were rendered useless by means of gas and demolition charges.

Operation Cedar Falls: A Disappointing Outcome

In Vietnam at War: The History: 1946-1975, former U.S. Army Lieutenant General Phillip Davidson describes the disappointing outcome of Cedar Falls. The enemy frustrated the fundamental principle of Westmoreland's plan by refusing to stand and fight, preferring to risk his bases rather than endanger his forces. Not only was the United States unable to bring the enemy to bay in his base areas, but the Viet Cong came back as soon as the American troops left. They returned to the Iron Triangle only two days after the U.S. pulled out of Operation Cedar Falls. As described in an official report, the base area was “literally crawling with what appeared to be Viet Cong” only ten days later.

No big headquarters or depots fell to the American assault troops, although they did seize some small arms and ammunition, and enough rice to feed a Viet Cong division for one year. The enemy had long before scattered his installations and hidden them deep underground. Only a year following the operation's conclusion, the Iron Triangle area was used as a staging ground for Tet Offensive attacks on Saigon. Compounding the lack of lasting results with negative aftereffects, measures such as saturation bombing and the forced relocation of civilian populations created a legacy of ill will towards the U.S.