III Corps was responsible for the densely populated, fertile military region between Saigon and the Highlands. This region includes ten provinces: Binh Duong, Binh Hyua, Binh Long, Binh Tuy, Hau Nghia, Long An, Long Kahnh, Phuoc Long, Phuac Tuy Tay Ninh. As of 1969 Lieutenant General Do Cao Tri's III CTZ surrounding Saigon included the Fifth Division at Phu Loi, the 18th Division at Xuan Loc and the 25th Division at Duc Hoa.
Đông Nam B? (literally "South-eastern region") is a region in modern Vietnam. This region includes one municipality, Ho Chi Minh City; and seven provinces: Dong Nai, Binh Duong, Ba Ria-Vung Tau Province, Binh Phuoc, Tay Ninh, Binh Thuan Province, and Ninh Thuan Province. This region is the most economically developed region in Vietnam. In 2006, this region contributed 148,000 billion VND (equal to $9.25 billion) out of 251,000 billion VND to the state budget. This region is also the highest urbanized in the country with more than 50% people living in urban area (while the same figure for Vietnam is just 25%).
During the Vietnam War, the III Corps tactical zone (III CTZ) was an Army of the Republic of Viet Nam organization with geographic responsibility for Saigon and 11 surrounding provinces. It had had various earlier names, such as Saigon Military District. The are contained 38 percent of the population and 90 percent of the industry. III CTZ headquarters was at Bien Hoa, a suburb northeast of Saigon. U.S. II Field Force Vietnam (II FFV), its counterpart organization, was based at Long Binh.
III Corps was the third allied combat tactical zone in South Vietnam. During the 1960s and early 1970s, the country was divided into four major administrative and military regions, and III Corps extended from the northern Mekong Delta to the southern Central Highlands. It was also known as Military Region 3 (MR 3). III Corps had its headquarters in Saigon, and consisted of the following provinces: Tay Ninh, Binh Long, Phuoc Long, Phuoc Tuy, Long An, Binh Duong, Long Khanh, Binh Tuy, Gia Dinh, Hau Nghia, and Bien Hoa. The 18th and 25th Divisions of ARVN (Army of the Republic of Vietnam) played prominent roles in the military defense of III Corps, as did the 2nd Armored Cavalry and the 81st Airborne Rangers.
Centered on the defense of Saigon, Westmoreland's concept of operations in the III Corps area had a clarity of design and purpose that was not always apparent elsewhere in South Vietnam. Nearly two years would pass before U.S. forces could maintain a security belt around the capital and at the same time attack the enemy's bases. But Westmoreland's ultimate aims and the difficulties he would encounter were both foreshadowed by the initial combat operations in the summer and fall of 1965.
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. Through his deputy senior adviser, a position established in 1967, the field force commander was able to keep abreast both of the activities of U.S. sector (province) and subsector (district) advisers and of the progress of Saigon's pacification efforts.
Roads were a major concern of U.S. commanders. In some operations, infantrymen provided security as Army engineers improved neglected routes. Defoliants and the Rome plow - a bulldozer modified with sharp front blades - removed from the sides of important highways the jungle growth that provided cover for Viet Cong ambushes. Road-clearing operations also contributed to pacification by providing peasants with secure access to local markets. In III Corps, with its important road network radiating from Saigon, ground mobility was as essential as airmobility for the conduct of military operations.
Although the combat effectiveness of ARVN units in III CTZ left much to be desired, there was an overall, and in some cases marked improvement in most units by early 1969. Lieutenant General DO CAO TRI, who assumed command of III Corps and III Corps Tactical Zone on 5 August 1968, was principally responsible for this improved combat effectiveness. His employment of general reserve battalions in areas distant from Saigon had the immediate effect of transforming III Corps from a relatively static posture to an offensive-oriented one. He employed an average of eight general reserve hattalions in this role since his assumption of command. Additionally, his emphasis on the spirit of the offensive, multi-day operations, US/ARVN/RF/PF combined operations, timely reaction to contacts, and removal of maneuver elements from province and district capitals had a very salutary effect.
Other factors which contributed to improved operational effectiveness were the issue of the M-16 and M-60, availability of greater quantities of the M-79, the activation of two additional maneuverbattalions and three artillery battalions, relief of many ineffective regimental, battalion and company comanders, more meaningful guidance emanating from corps level, battalion training programs conducted by US units, and the growing realization among ARVN units that they can attack the NVA/VC decisively on the battlefiald.
During 1968 and early 1969 the 5th and 25th Divisions conducted extensive and frequent combined operationw with units; this was not the case for the 18th Division, due to the absence of any major US unit in the 33d DTA. Fifteen maneuver battalions remained in direct support of Revolutionary Development, six from the 5th Division, four from the 18th Division, and five from the 25th Division. Additionally, two battalions from the 18th Division remained on static security missions directed by III Corps. Thus, 17 of the 36 infantry maneuver battalions orpanic to III Corps were not available to their commanders for extended field operations. In terms of overall combat effectiveness and results of operations, the 25th Division was adjudged to be the best division in III Corps. The 5th and 10th Divisions were both considered marginal in terms of cambat effectiveness and overall results.
During 1968 and early 1969 III Corps units conducted an average of 14 combat assaults per week. Their technique in conducting air mobile operations had improved considerably. The 25th ARVN Division was very accomplished in this regard and their proficiency in such was coparable to that of US units. The 5th and 18th ARVN Divisions had not yet reached this degree of proficiency, but did a creditable job and continued to improve.
By early 1969 III CTZ ARYN units had a long way to go before attaining satisfactory combat effectiveness by US standards. The principal deficiencies continued to be a low level of leadership, serious imbalances in grade structure, lack of supervision by the chain of command, the prevalent belief by commanders that excessive friendly losses were tantamount to relief, over-centralization of authority, lack of operational responsiveness, a great reluctance to conduct independent or semi-independent small unit operations, weak coordination of fire supprt, the stronp tendency to conduct search operations in column formation, poor security on operations, ineffective employment of cavalry units, an excessive desertion rate, inadequate promotion and schooling policies, and a weak program for ministering to the individual needs of the soldier and his family.
The Cambodian operation in which Company A, 5th Special Forces Group, participated was the high point in combat operations in III Corps in 1970. Civilian Irregular Defense Group companies from the camps at Duc Hue and Tra Cu assaulted a Viet Cong training area in Cambodia and discovered caches that provided over one-third of all the crew-served weapons captured during the May offensive. The Civilian Irregular Defense Group troops not only captured equipment, but also killed eighty of the enemy. Earlier in 1970 the III Corps CIDG Mobile Strike Force distinguished itself by capturing an enemy cache of record size. The action took place in War Zone D near Rang Rang, an area which traditionally had been an enemy stronghold. The strike force picked up 450 SKS carbines, 1,034 82-mm. mortar rounds, 130 122-mm. rockets, and almost 200 tons of rifle and mortar ammunition. The camps at Katum, Tong Le Chon, and Bu Dop were all subjected to heavy mortar attacks, with Katum, the heaviest hit, receiving for one period close to 300 rounds a day. After the Cambodian operations, as in II Corps, things quieted down.
The tragic death of General Do Cao Tri in a helicopter crash in February 1971 marked a major turning point of thewar in South Viet Nam. LTG Nguyen Van Minh, succeeding General Tri as III Corps Commander, made mistake after mistake from the very start. Because of his weakness, the ARVN suffered many setbacks and, little by little, lost the initiative to the enemy.
In the spring of 1975, Giap launched another "final" offensive with a total of one hundred thousand troops (half the 1972 number). For 14 days and nights from 11 to 25 April 1975, III Corps Armored Task Force [ATF] reinforced by the 8th Regiment of the 5th Infantry Division fought and stopped a ferocious NVA corps advance near the junction of National Routes 1 and 20 as part of the epic battle of Xuan Loc, the war's bloodiest.
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