I Corps (known as Eye Corps) was the northernmost of the four major military and administrative units of South Vietnam in the 1960s and early 1970s. Also known as Military Region 4 (MR 4), I Corps was one of four allied tactical combat zone. I Corps was responsible for the Provinces of Quang Tri, Thua Thien, Quang Nam, Quang Tin, Quang Ngai, Hue, and Da Nang. As of 1969, Lieutenant General Hoang Xuan Lam's I CTZ, embracing the five northern provinces, there were the First Division at Hue, the Second Division at Quang Ngai, the 51st Independent Regiment at Hoi An and the 54th Independent Regiment at Tam Ky.
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. A similar arrangement was set up in I Corps, where the commander of the III Marine Amphibious Force was the equivalent of a field force commander.
The Central Lowlands of South Vietnam extend along the sea from the Mekong Delta northward to the Demarcation Line. On the landward side, the ChaIne Annamitique rises precipitously above the Lowlands and, in some areas, is nearly 40 miles inland; elsewhere it veers shoreward and at several points crowds into the sea. In general, the land is fertile and is extensively cultivated. The chief crop is rice, and considerable sugarcane is also grown. Fishing is good along the entire coast and is important both as an industry and for local subsistence in the southern section near the Mekong Delta.
From Mui Dieu / Tuy Hoa to Da Nang, about 250 miles north, lie the most extensive and fertile plains of the Central Lowlands coast where two rice crops a year are grown. From Da Nang to Hue, about 50 miles farther north, mountain spurs jut into the sea at several places. From Hue to the 17th parallel-50 miles beyond-much of the shore is fringed by it narrow line of sand dunes backed by 'an intensively cultivated flat fertile area.
In the Central Lowlands two distinct types of village predominate. The fishing village, strung out along the coastal plain, usually consists of a close-knit group of dwellings located in a sheltered cove or bay. In the second type of 'v.ilIage, fishing is not the major economic activity and its formation follows a pattern similar to that of the delta with houses more dispersed over a broader area.
There were certain differences between operational concepts of the US Army and the US Marine Corps. Concentrating their efforts in the coastal districts of I Corps and lacking the more extensive helicopter support enjoyed by Army units, the USMC avoided operations in the highlands. On the other hand, Army commanders in II Corps sought to engage the enemy as close to the border as possible and were quick to respond to threats to Special Forces camps in the highlands.
In I Corps, the enemy seemed intent on dispersing American forces to the border regions. Heightened activity along the demilitarized zone drew marines from southern I Corps. To replace them, Army units were transferred from III and II Corps to the area vacated by the marines, among them the 196th Infantry Brigade, which was pulled out of Operation JUNCTION CITY, and the 3d Brigade, With Infantry Division, which had been operating in the II Corps Zone. Together with the 1st Brigade, 101st Airborne Division, these units formed Task Force OREGON, activated on 12 April 1967 and placed under the operational control of the III Marine Amphibious Force. Army infantry units were now operating in all four of South Vietnam's corps areas.
By the end of 1967, progress in pacification in both I Corps and country-wide was very much in the eye of the beholder. At the end of 1967, despite some feeling of optimism, there were continuing doubts about progress in pacification both in I Corps and the country at large. From both American and South Vietnamese sources came indications of increased enemy offensive intentions. This was especially true in I Corps where the allies expected another large enemy push in the north.
Initially, the enemy Tet offensive was a tremendous setback for both the Marine and country-wide pacification program. With the attacks on the major cities of Vietnam and especially the one-month battle for Hue, the enemy added an entire new dimension to the war. The enemy attacks during the holiday period resulted in an enormous increase of new refugees, ranging from estimates of 750,000 to over a million, with nearly 170,000 in I Corps and, of that number, about 75,000 from the city of Hue. The Communists may never have realistically expected their Tet offensive to cause an uprising throughout South Vietnam. At least in I Corps, their main objective was not Khe Sanh, but Hue. They perhaps hoped that the capture of Hue would result in the defection of the South Vietnamese forces and the loss of other population centers in the two northern provinces of South Vietnam. This would have left the Communists in a strong position for obtaining their own terms. With the securing of the city of Hue, the enemy's countrywide Tet offensive had about spent itself.
As in other areas, pacification in southern I Corps seemed to improve after the 1968 Tet offensive, though enemy units still dominated the Piedmont and continued to challenge American and South Vietnamese forces on the coast. Operations against them proved to be slow, frustrating exercises in warding off NVA and Viet Cong main force units while enduring harassment from local guerrillas and the hostile population.
In May of 1968, there were 98 maneuver battalions in the I Corps area of which 26 were U.S. Marine Corps, 31 were U.S. Army, 37 were Vietnamese, and 4 were Republic of Korea. This total, 196, was somewhat above the June figure and is indicative of the fluid situation. The U.S. maneuver battalions were assigned to the 1st and 3d Marine Divisions, 1st Cavalry Division (Airmobile), 101st Airborne Division, and the Americal Division; the Vietnamese Army battalions were normally assigned to, or under, the operational control of the 1st and 2d Vietnamese Army Divisions and the 51st Independent Infantry Regiment. The four Republic of Korea battalions were under the 2d Republic of Korea Marine Brigade which, although not under the operational control of the III Marine Amphibious Force, was generally treated as such for planning and coordinating purposes.
The North Vietnamese Army and the Viet Cong continued to be active in I Corps during 1970. Company C, 5th Special Forces Group, was charged with Special Forces operations in I Corps. The camp at Tien Phuoc achieved one of the highest kill ratios of any camp in the zone in 1970. For a period of two to three months, the camp averaged 50 to 60 of the enemy killed each month and itself suffered few casualties. The camp at Mai Loc received an early morning sapper attack in which most of the camp structures were destroyed before the CIDG troops succeeded in driving the Viet Cong out. Shortly after the attack on Mai Loc, the camp at Thuong Duc was taken under siege by the enemy, who used mortar and rocket barrages. The siege lasted sixty days, but the camp held out. Again, in October, Thuong Duc came under attack, but the camp defenders seized the initiative and in a three day period killed 74 of the enemy by small arms alone. Over a seven-day period, three heavy battles resulted in a final total of 150 of the enemy killed.
On 4 March 1975, the Communist People's Army of Vietnam (PAVN) launched the final campaign of its 30-year war. On 8 and 9 March, the NVA/VC started Phase l of their Spring/Summer Campaign. The VC units that infiltrated into the lowlands were unable to gain the support of the population. The population, in fact, appeared to be very much afraid of the VC and fled. Without popular support, the VC were quickly isolated, dispersed and eliminated by GVN forces. Total NVA/VC casualties during Phase I of the campaign were approximately 750 killed and over 50 captured. GVN losses were less than 200 killed and missing. Morale, subsequent to, the GVN's success in repulsing Phase I of the NVA/VC Spring/Summer Campaign, appeared good; however, on 15 March, LTC Do Ky, Quang Tri Province Chief, related that the military, political and economic situation in MR 1 was like that of a very strong person who was. seriously infected with a terminal disease. He said that the skin, eyes and hair may appear healthy and the individual may even feel well, but that death was imminent. LTC Ky said the problem in South Vietnam and I Corps was that no one wanted to take the responsibility for making a decision. He said the Marine Division was being redeployed from Quang Tri Province to the Da Nang area, but that no one had determined whether to defend Quang Tri Province. LTC Ky said the Marines were the heart of Quang Tri Province and without them the people would not stay. He also said that he did not have sufficient forces to defend Quang Tri Province without the marines.
Confused, desperate, and in what must have been a virtual state of shock, South Vietnamese President Nguyen Van Thieu made momentous decisions on 10 and 11 March that sealed the fate of South Vietnam. Thieu's first move was to order the immediate recall of the ARVN Airborne Division, the cornerstone of the defense of I Corps, to shore up Saigon's defenses. As ARVN commanders tried to withdraw units and redeploy to fill the gap left by the Airborne's pull-out, the defenses of I Corps began to teeter like a house of cards.
On 16 March, the 369th Marine Brigade moved out of Quang Tri Province. On 16 or 17 March, LTC Ky suggested that GVN civil servants and military personnel evacuate their dependents. In MR 1, North Vietnamese Army (NVA) gains during the first phase of the offensive, combined with the deployment of the Marine Division from Quang Tri to Da Nang and the withdrawal of the Airborne Division, triggered a mass civilian exodus from Quang Tri on 17 March. The evacuation of the civilian population from Quang Tri Province was almost complete. Some estimates were as high as 95%. There was some artillery and rocket fire along QL 1 during the evacuation, but casualties were light. The Quang Tri refugees streamed into Hue. Initial reports indicated that up to 95% of the population of Quang Tri relocated to Hue. Many moved in with relatives or friends; others had no place to stay and grouped along the streets. No GVN effort was made to funnel the refugees into camps and no real police effort was made to check identification papers. The influx of refugees into Hue and rumors that the Government of Vietnam (GVN) was going to forfeit Quang Tri and Thua Thien Provinces started a mass evacuation of Hue on 18 March.
Concurrent with that exodus, on the night of 18 March, all US Government employees continued to conduct liaison in Da Nang. Selected US employees continued to conduct liaison in Hue during daylight hours until 23 March when 30 rounds of 122mm artillery impacted near the US compound. By 24 March, I Corps Forward and its subordinate units had been withdrawn to Da Nang. By 25 March, Da Nang contained more than a million people, half of whom were civilian and military refugees from Quang Tri and Thua Thien Provinces. The failure of the GVN to control the refugee situation prompted the US Consul General (ConGen) in Da Nang to start evacuating US dependents. The massive evacuation of US civilian and Local National (LN) US Government employees started in earnest on 26 March; however, by 2000H hours that evening crowds at the airport were impeding the loading of contract aircraft. As legitimately manifested US citizens, Vietnamese and Third Country Nationals (TCN's) attempted to board waiting aircraft, RVNAF members and their farmlies, previously hidden among the airport buildings rushed the loading ramps and entered the aircraft. By 0600H hours on 27 March, refugees had crowded the airport and were on parts of the runway. During that afternoon and evening, in attempts to load legitimate passengers, aircraft were parked and loaded in isolated areas or passengers were helicopter lifted to Marble Mountain airstrip and evacuated to Nha Trang by Air America cargo aircraft.
As the refugee situation at the airport suspended the airlift, the ConGen was forced to shift to sealift operations. On the evening of 27 March, remaining US employees and TCN's were assembled at the Alamo Annex Apartments and the ConGen compound. At 0400H on 28 March, the ConGen authorized the final evacuation of Da fang. The remainder of the US evacuees, LN employees and refugees were loaded on barges and transported to commercial ships. As US citizens were being loaded, evacuation vessels were also forced to take on refugees riding tugboats and sampans. All vessels were overloaded and ill equipped to handle feeding and security. By one estimate, approximately 20-25% of those evacuated were RVNAF members. After loading, the ships departed Da Nang and arrived approximately 20 hours later at Cam Rank Bay. From Cam Ranh, US employees were flown to Saigon.
By 29 March, Hue, Da Nang, and all of ARVN I Corps were in communist hands.
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