The IV Corps () was a corps of the Army of the Republic of Vietnam (ARVN), the army of the nation state of South Vietnam that existed from 1955 to 1975. It was one of four corps in the ARVN, and it oversaw the Mekong Delta region of the country.
The Mekong Delta was the heartland of agricultural South Vietnam, it encompassed the fertile alluvial plains formed by the Mekong River and its main tributary, the Bassac River. With its sixteen provinces, the Delta contained about two-thirds of the nation's population and yielded the same proportion in rice production. The terrain of IV Corps differed radically from other regions. Flat and mostly uncovered, it consisted of mangrove swamps and ricefields crisscrossed by an interlocking system of canals, natural and artificial. Except for some isolated mountains to the west near the Cambodian border, few areas in the Delta had an elevation of more than above sea level. During the monsoon season, most of the swampy land north of Route QL-4, generally called the Plain of Reeds, was inundated, especially when alluvial waters raised the level of the Mekong River from July to October. Other undeveloped swampy areas along the coast had turned into havens that sheltered Viet Cong (VC) main force units just as the scattered bases inland offered good refuge for local guerrillas.
History 1957-1961 IV Corps headquarters was located at Mỹ Tho with its assigned unit being the 16th Light Division.
The 7th Division based in Mỹ Tho, and due to the division's close proximity to the capital Saigon was a key factor in the success or failure of the various coup attempts in the nation's history. In the coup attempt of 1960, the loyalist Colonel Huỳnh Văn Cao used the 7th Division to storm into Saigon to save President Ngô Đình Diệm.
1962 In 1962, Diem decided to split the command of the area in the south around Saigon into two, the former III Corps area being reduced in size to cover the area northeast of Saigon, and the newly created IV Corps taking over the west and southwest. Cao was promoted to general and assumed command of the new IV Corps Tactical Zone, which included the area of operations of his 7th Infantry Division.
On 15 April the United States Marine Corps began Operation Shufly to improve the mobility of ARVN forces by deploying a Marine helicopter squadron to Soc Trang Airfield.
On 24 April 16 USMC helicopters supported the 21st Division in Operation Nightingale conducted near Can Tho. The operation resulted in 70 VC killed and three captured for the loss of three ARVN killed.
In early September 1962, the USMC Shufly squadron began redeploying with its support units to Da Nang Air Base in I Corps, completing the redeployment by 20 September. Simultaneously the United States Army's 93rd Helicopter Company moved from Da Nang to Soc Trang.
1964 On 30 January 1964 General Nguyễn Khánh overthrew General Dương Văn Minh in a bloodless coup. By 6 March Khánh had replaced three of the four Corps commanders. Khánh replaced General Nguyễn Hữu Có with a political supporter, Brigadier general Dương Văn Đức as Corps' commander.
On 24 February 1964 Khánh issued the 1964 National Campaign Plan under the name Chien Thang (Struggle for Victory). Khanh decided the provinces surrounding Saigon would receive top priority in the distribution of troops, civil servants, and money. The rest of III Corps and IV Corps were next in the resource queue, whereas the provinces of II and I Corps had the lowest priority. One reason why the north received the least resources was that, at least before late 1963, it had appeared to be in the best shape. Thus, Chien Thang forecast that I and II Corps would be the first to enter into the final phase, the destruction of the enemy's last major formations and bases in January 1965, whereas III and IV Corps would not reach that point until January 1966.
The Corps' two infantry divisions and territorials numbered about 52,000 men. The allies estimated that the VC had 5,000 regulars and 25,000 guerrillas, yielding the lowest government-to-enemy advantage of any Corps' zone. Here, as throughout the country, the VC targeted the territorials. On average, an ARVN battalion engaged the VC once every two weeks, and Civil Guard companies made contact two out of every three days.
By mid-1964 IV Corps had made some progress, all provinces had approved Chien Thang plans. The Corps had received a psychological warfare battalion, and the command had imposed a nighttime curfew on all waterways to improve resources control. The ARVN were conducting more operations and had made significant progress in consolidating static forces into more mobile formations. Between October 1963 and March 1964, the number of small posts in the delta had declined from 1,300 to 850. However the Corps was below its authorized strength of 21,025 regulars, with a foxhole strength of just 10,174 men.
The VC summer offensive in IV Corps generated a 46 percent increase in insurgent-initiated incidents during the third quarter of 1964 over the previous one. As elsewhere in South Vietnam, the VC handed the government some embarrassing reverses. However, in many instances, government troops had performed well, backed by U.S. aviation whose presence sometimes made the difference between victory and defeat, or between defeat and disaster. As far as pacification was concerned, nearly every province in IV Corps reported slight gains in the number of people living under government control/influence.
On 5 September, the Joint General Staff (JGS) abolished the Tien Giang Tactical Area. It transferred the 7th Division and four of the five provinces it supervised to IV Corps and assigned Long An Province to III Corps.
On 13 September, Corps' commander Đức, together with former III Corps commander Brigadier general Lâm Văn Phát, launched an abortive coup against Khánh, sending the 7th Division into Saigon. The coup failed to gain support and by the next day had unravelled. Khanh then replaced three of the four corps commanders, six of the nine division commanders, and a third of all province chiefs. General Nguyễn Văn Thiệu was appointed as the new Corps commander. The government created two new provinces in IV Corps, forming Bac Lieu from portions of Ba Xuyen and Chuong Thien, and Chau Doc by taking several districts from An Giang province.
When COMUSMACV General William Westmoreland visited IV Corps in late 1964, he expressed relief at the "bright outlook" he found in the delta. Westmoreland believed what the delta needed was not more regular soldiers, it already had three of South Vietnam's nine divisions, but more and better trained police, civilian cadre, and territorials. These were the key to the "hold" part of clear-and-hold operations. Without them, government control would not be able to take root and expand, for the ARVN would be tied down protecting communities to such a degree that it would be unable to combat the VC’s growing conventional military forces.
In addition to having to deal with the VC, the Corps also had to deal with increasingly bellicose Cambodian forces as the ARVN engaged or pursued VC forces near and across the Cambodian border.
A year-end survey by the Corps' new senior adviser, found that only three of 15 sector advisers felt pacification was proceeding satisfactorily. Population control was assessed to have declined from 60% in January to 58% in December.
By the end of 1964 a US Army helicopter aviation company or US Marine Corps helicopter squadron was assigned in direct support of each Vietnamese infantry division, with two additional helicopter companies in general support of III and IV Corps. Further fixed-wing transport, reconnaissance, and observation aircraft were available as well. As a result, each senior Corps adviser had between 70 and 100 aircraft at his disposal, with MACV retaining control over the rest.
1965 During the first three months of 1965 VC regulars kept largely to their bases, in part because COSVN directed the region to focus on building forces and sending troops north for operations in more important theaters. Small-scale ambushes and forays against hamlets and outposts, interspersed by brief bombardments of district towns, were about the best the Front could muster. Still, the VC remained active, with IV Corps accounting for 31% of all attacks nationwide during the first quarter of the year.
Just as the VC focused its strategy farther north, so too did the South Vietnamese. The pacification plan continued earlier policy in assigning IV Corps a low priority. For 1965, the Corps was to maintain existing areas of government control while gradually expanding the oil spots where it could. However, unlike the rest of the country, the Corps kept 50% of its regular army forces free for mobile operations, a far higher number than in any other part of South Vietnam, to strike VC bases to disrupt their ability to launch major operations. Thieu focussed on creating a belt of government control running from east to west across the upper delta. This would both enhance Saigon's security and cut off the VC farther south from the rest of the country. As always, he stressed the importance of keeping open Highway 4, over which trucks carried 2 million tons of food annually to Saigon.
In January the government promoted Thieu to Lieutenant general and brought him to Saigon. The Joint General Staff then assigned the commander of the 21st Division, Major general Đặng Văn Quang, to command IV Corps and sent the Army's Chief of Military Security, Colonel Nguyen Van Phuoc, south to command the 21st Division.
Although the government won several victories during the first three months of the year in IV Corps, these engagements had not altered significantly the situation on the ground. If the inability to protect the Corps' many far-flung communities from small-scale acts of terror and harassment contributed to the problem at one end of the scale, so too did the VC's big battalions on the other end of the spectrum. Here, as well as elsewhere in the country, the VC's ability to keep these units largely intact acted as a powerful deterrent against the government conducting small-scale security operations. Even during periods of relative inactivity, the mere possibility that government troops might encounter an enemy battalion discouraged commanders from operating in squad, platoon and company strength. By the end of March, the number of the Corps' 4.2 million people living under government control had crept up slightly, from 31% to 33%.
In April, Westmoreland convinced the JGS to order the commanders of I, II, and IV Corps to develop Hop Tac-style pacification programs for their areas. After receiving joint MACV-JGS briefings about the program, the commanders presented their plans on 3 May. IV Corps was to create a Hop Tac program centered on Can Tho.
From 4 to 6 April the 21st Division conducted Operation Dan Chi 129 against the VC stronghold in the U Minh forest in Kiên Giang province killing 278 VC for the loss of five ARVN and six US killed.
Thanks in part to the efforts of the 7th Division and the other security forces in IV Corps, not to mention the VC's decision to transfer troops out of the delta to strengthen holdings elsewhere, the situation in IV Corps was relatively stable by mid-1965. The VC still controlled significant numbers of people and vast tracts of land, but the South Vietnamese usually were able to keep the main roads, rivers, and canals open. The government had managed to secure 276 delta hamlets, adding 300,000 more people to the rolls of those living under its control.
By late 1965 Westmoreland considered Quang, to be "an excellent corps commander and leader." Yet continued charges of corruption and his close political ties with his predecessor, Thiệu, clouded his professional reputation. Assessments of Quang's three major subordinates were, in the main, positive.