IV Corps was the southernmost of the four major military and administrative units of South Vietnam in the 1960s and early 1970s. Its headquarters were located at Can Tho in the Mekong Delta. Also known as Military Region 4 (MR 4), IV Corps was the fourth allied tactical combat zone. It consisted of the following provinces: Chau Doc, Kien Phong, Kien Tuong, Hau Nghia, Kien Giang, An Giang, Vinh Long, Dinh Tuong, Long An, Chuong Thien, Phong Dinh, Vinh Binh, Kien Hoa, Go Cong, An Xuyen, Bac Lieu, and Ba Xuyen.
In the Mekong Delta, where the worst abuses of tenancy and landlordism prevailed, the Viet Minh found ready support in the villages during the years of the Indochina War. Throughout this period the Viet Minh forces lived off the land. Where they controlled the countryside, they imposed tax burdens in grain as heavy as the rentals formerly collected by the landlords. They did so not only by their power to coerce but also by convincing the peasants that they represented the cause of national liberation. Though the Viet Minh had no specific land program, the landless were led to believe that the landlord's property would belong to them as soon as the French were defeated. Many landlords had fled and those who normally lived in Saigon did not dare to venture outside the city. Peasants were encouraged to take over abandoned land, and payment of rent, as distinguished from taxes, virtually ceased.
Quasi-military religious sects, such as the Hoa Hao and the Cao Dai, gained control over substantial areas of the Mekong Delta along the Cambodian border where, citing traditional concepts of land usage, they also encouraged peasants to occupy abandoned land without regard to legal titles. As a result of all these factors, a virtual land reform program had been carried out in this area before independence.
Because of the nature of its terrain, and more important, its geographical isolation from major North Vietnamese strongholds, the Delta area had generally been infiltrated by enemy guerrilla or small force rather than large force bands. Thus, except for the Mobile 3 Riverine Force and small Special Forces units, no U.S. troops had normally operated in the area until Operation Deckhouse V in 1967 when the U.S. 9th Infantry initiated two years of intensive antiguerrilla activities. Otherwise, MR 4 had been and continued to be primarily a Vietnamese area of operations.
As of 1969, in Major General Nguyen Van Minh's IV CTZ, in the populous Mekong Delta, there were the Seventh Division at My Tho, the Ninth Division at Sadec and the 21st Division at Bac Lieu. The 7th and 9th ARVN Divisions (Army of the Republic of Vietnam) played major roles in IV Corps military activities. The United States Ninth Infantry Division operated extensively throughout IV Corps, attacking Vietcong units in their strongholds in the Plain of Reeds, the U Minh Forest, and the Seven Mountains areas.
As the number of Army combat units in Vietnam grew larger, Westmoreland established two corps-size commands, I Field Force in the II Corps area and II Field Force in the III Corps area. Reporting directly to the MACV commander, the field force commander was the senior Army tactical commander in his area and the senior U.S. adviser to ARVN forces there. Working closely with his South Vietnamese counterpart, he co-ordinated ARVN and American operations by establishing territorial priorities for combat and pacification efforts. Only in IV Corps, in the Mekong Delta where few American combat units served, did Westmoreland choose not to establish a corps-size command. There the senior U.S. adviser served as COMUSMACV's representative; he commanded Army advisory and support units, but no combat units.
To patrol and fight in the inundated marshlands and rice paddies and along the numerous canals and waterways crossing the Delta, the US Army modernized the concept of riverine warfare employed during the Civil War by Union forces on the Mississippi River and by the French during the Indochina War. The Mobile Riverine Force utilized a joint Army-Navy task force controlled by a ground commander. In contrast to amphibious operations, where control reverts to the ground commander only after the force is ashore, riverine warfare was an extension of land combat, with infantry units traveling by water rather than by trucks or tracked vehicles. Aided by a Navy river support squadron and river assault squadron, infantrymen were housed on barracks ships and supported by gunships or fire support boats called monitors. Howitzers and mortars mounted on barges provided artillery support.
Combat operations in IV Corps during 1970 continued to be centered around the special techniques the 5th Group had developed for using the waterways in the Mekong Delta to wage war. The Delta Company Strike Force made heavy use of sampans and airboats in its operations. The Seven Mountains region was again the scene of heavy fighting when strike force troops, along with strike forces from Camps Ba Xoai and Vinh Gia, moved in to clear the area. Ba Xoai and the B detachment at Chi Lang both repulsed enemy attacks on those camps. As a whole, IV Corps operations indicated that in the delta especially the Vietnamese were fully capable of running the war on their own.
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