War Zone C lay in the heavily wooded area to the north of Saigon and bounded by the Cambodian border. During late 1966 the Americans became aware that the Viet Cong (VC) guerrillas had established a vast complex of underground tunnels in the region, little realizing that these tunnels to be far more sophisticated and complex than they imagined. Some of the tunnels would stretch for 20 miles; with the Viet Cong having established whole communities underground, complete with accommodation, schools, hospitals, recreational areas and even munitions factories.
To find and eliminate the VC bases in the region the US Army, in mid September, tasked the 196th Infantry Brigade to carry out a Search and Destroy operation (code named Operation Attleboro). At first no significant contacts were made with the enemy although intelligence reports were suggesting that the 9th VC division, which had been mauled by the 1st Infantry Division during Operation El Paso II, had moved into the area from its sanctuaries in Cambodia. Then in October a major VC base camp was uncovered in the area confirming that the VC had indeed entered the region in some strength. To aid the 196th in their mission, elements of the 1st Infantry Division were moved into the area, and on October 28th the GIs made contact with a VC battalion and uncovered a number of enemy base camps. After a pounding by artillery and aircraft, the GIs searched for bunkers and sealing the tunnel entrances with grenades, before pumping in oxy-acetylene gas which was then exploded with dynamite.
By the first week of November it was apparent that a very large enemy force was in the area. To back up the units already in the field, brigades from the 4th and 5th Infantry Divisions and the 173rd Airborne Brigade were brought in until some 22,000 American troops were actively engaged in the operation. This made Attleboro the largest ground operation of the war to date.
Throughout November the fighting continued as the various units tried to encircle the elusive guerrillas and at the end of November the remaining communists of the 9th Division slipped back across the border into neighbouring Cambodia. Finally, after 72 days of action, the operation petered out. It had cost the Americans 150 killed and 500 wounded against a ‘claimed’ enemy body-count of 2,200 dead and 900 wounded.1