In the wake of the failed South Vietnamese Operation Lam Son 719, the Hanoi leadership began discussing a possible offensive during the 19th Plenum of the Central Committee of the Vietnam Workers' Party in early 1971. By December, the Politburo had decided to launch a major offensive early in the following year. 1972 would be a U.S. presidential election year, and the possibility of affecting the outcome was enticing and there was increasing anti-war sentiment among the population and government of the U.S. With American troop withdrawals, South Vietnamese forces were stretched to breaking point along a border of more than 600 miles (966 km) and the poor performance of ARVN troops in the offensive into Laos promised an easy victory.
This decision marked the end of three years of political infighting between two factions within the Politburo: those members grouped around Trường Chinh, who favored following the Chinese model of continued low-intensity guerrilla warfare and rebuilding the north and the "southern firsters" around Defense Minister Võ Nguyên Giáp, supported by First Party Secretary Lê Duẩn (both of whom supported the Soviet model of big offensives). The failure of the Tet Offensive of 1968, had led to a downgrading of Giap's influence but the victory achieved over South Vietnamese forces during the Laotian incursion, brought Giap's strategy back into the ascendant. Lê Duẩn was given responsibility for planning the operation but Giap never rose to his former prominence, dealing chiefly with logistical matters and the approval of operational planning. The officer entrusted with the conduct of the offensive was the PAVN chief of staff, General Văn Tiến Dũng.
The central questions then became where and with what forces the offensive would be launched and what its goals were to be. North Vietnam had used the border regions of Laos and Cambodia as supply and manpower conduits for a decade and a demilitarized zone that separated the two Vietnams. There, the line of communication would be shortest and forces could be concentrated where "the enemy is weakest...violent attacks will disintegrate enemy forces...making it impossible for him to have enough troops to deploy elsewhere." This was an important consideration, since the northern thrust would serve to divert South Vietnamese attention and resources, while two other attacks were to be launched: one into the central highlands, to cut the country in two and another eastwards from Cambodia to threaten Saigon.
Republic of Vietnam: Corps Tactical Zones
The offensive was given a title steeped in Vietnamese history. In 1773, the three Tây Sơn brothers (so-called because of the place of their origin) united a Vietnam divided by civil war and social unrest. The youngest brother, Nguyễn Huệ, then defeated an invading Chinese army on the outskirts of Hanoi in 1788.
The campaign eventually employed the equivalent of 14 divisions but decisive victory was not part of the North Vietnamese strategy. The goals were much more limited. There was the distinct possibility of destroying or at least crippling large elements of the ARVN; possibly deposing of South Vietnamese President Nguyễn Văn Thiệu; convincing the U.S. as to the hopelessness of continued support to the South and demonstrating the failure of Vietnamization. The prospect of seizing a South Vietnamese provincial capital, which could then be proclaimed as the seat of the Provisional Revolutionary Government, was also enticing. The attitude of the North Vietnamese leadership was illustrated in an article in a 1972 party journal: "It doesn't matter whether the war is promptly ended or prolonged...Both are opportunities to sow the seeds; all we have to do is to wait for the time to harvest the crop."
The northern leadership was taken aback during the summer of 1971, when an announcement was made that U.S. President Richard Nixon would visit the People's Republic of China, on a diplomatic mission before May 1972. The Chinese placated the suspicions of their ally, by reassuring North Vietnam that even more military and economic aid would be forthcoming in 1972. The Soviet Union, perceiving the growing antagonism between the People's Republic and North Vietnam, sought to widen the rift by also agreeing to "additional aid without reimbursement", for North Vietnam's military forces.
These agreements led to a flood of equipment and supplies necessary for a modern, conventional army. This included 400 T-34, T-54 and Type 59 (a Chinese version of the T-54) medium and 200 PT-76 light amphibious tanks, hundreds of anti-aircraft missiles, including the shoulder-fired, heat-seeking SA-7 Strela (called the Grail in the West), anti-tank missiles, including the wire-guided AT-3 Sagger and heavy-caliber, long-range artillery. To man the new equipment, 25,000 North Vietnamese troops received specialized training abroad, 80 percent of them in the Soviet Union or Eastern Europe. A contingent of high-level Soviet military personnel also arrived in Vietnam and stayed until March 1972 in preparation for the offensive.
During late 1971, U.S. and South Vietnamese intelligence estimates of communist intentions were mixed. An offensive was expected but intelligence as to its timing, location and size were confusing. The communists had mounted an offensive inside South Vietnam in 1968 but it was conducted mainly by the southerners of the NLF, who had been destroyed in the process. Without NLF support inside South Vietnam, a large-scale PAVN offensive was considered highly unlikely. A North Vietnamese thrust across the DMZ was also considered unlikely. Past infiltration and offensive operations had been conducted through and from Laotian and Cambodian territory and a DMZ offensive would be a blatant violation of the Geneva agreement, which North Vietnam was adamant in defending.
In December, intelligence became conclusive, PAVN units supporting Khmer Rouge operations in Cambodia, began returning to the border areas. In Laos and Cambodia, there was also an unusual expansion of infiltration. Within North Vietnam, there was a noticeable increase in military recruitment. In January, Defense Intelligence Agency officers briefed Secretary of Defense Melvin Laird, stating that PAVN would attack after the Tết holidays and that the offensive would make widespread use of armored forces. Laird was unconvinced, telling the United States Congress in late January, that a large communist offensive "was not a serious possibility".
U.S. and South Vietnamese intelligence services, had no consensus as to communist intentions. MACV, on the other hand, was suspicious. It sent several reconnaissance teams into the Mụ Giạ and Ban Karai pass areas and they discovered a buildup in PAVN forces and equipment. MACV then decided that the North Vietnamese were preparing for an offensive in the central highlands and the northern provinces of South Vietnam. The brunt of an attack would be borne by South Vietnamese forces, since U.S. strength had been reduced to 69,000 troops, most of whom were in support roles and that number was to be reduced to 27,000 by 30 November.
The U.S. commander, General Creighton W. Abrams, was convinced an offensive was likely but he was also convinced that the attack would begin during or near the Tet holidays, at the beginning of the year. He notified Admiral Thomas Moorer, chairman of the Joint Chiefs of Staff that the North Vietnamese might attempt to "duplicate the effects of the 1968 offensive, perhaps by a limited operation aimed less at inflicting defeat on the battlefield than in influencing American public opinion." The consensus at MACV was that such an offensive would be launched against II Corps, in the Central Highlands. When the offensive did not occur, he and his headquarters were ridiculed in the American press, for crying wolf. The moment of crisis seemed to have passed and by the end of March, allied forces that had been standing by were returned to pacification efforts. U.S. Ambassador, Ellsworth Bunker, left for Nepal, while General Abrams went to Thailand to spend the Easter holiday with his family.
The Nguyen Hue Offensive
The ARVN units upon which the initial North Vietnamese attack was to fall, included the 1st and 3rd Infantry Divisions in Quảng Trị and Thừa Thiên Provinces and the 2nd Division, further south. This force was supplemented by two brigades of Marines (the 147th and 258th), the 51st Infantry Regiment, the 1st Ranger Group and Regional and Popular Forces – approximately 30,000 men. The units were in static defensive positions and lacked adequate mobile reserves.
Bearing the initial brunt of the attack would be the 3rd Division, created in October 1971 and located in an arc of outposts near the DMZ, to replace departing American troops. To create the new unit, the 1st Division (arguably ARVN's best unit) was stripped of its 2nd Regiment and the 11th Armored Cavalry was brought up from the I Corps reserve. Both units were experienced, well-trained, equipped and led. The 3rd Division's other two regiments, the 56th and 57th were made up of recaptured deserters, men released from jail and regional and provincial forces. It was led by cast-off officers and sergeants from other units. Like other ARVN units at this stage of the conflict, the division was suffering from a dearth of American advisors, who by then served only at regimental, brigade and divisional headquarters.
Because of the general belief that the North Vietnamese would not violate the sacrosanct boundary, the unit was stationed in the relatively "safe" area directly below the DMZ. The division was commanded by newly promoted Brigadier General
Vu Van Giai, the former deputy commander of the 1st Division. The I Corps commander, Lieutenant General Hoàng Xuân Lãm was an officer who epitomized the indecision and ineffectiveness of Saigon's command structure, as had been discovered all too blatantly during Operation Lam Son 719. Lam concentrated on administrative matters and left tactical decisions to his subordinate commanders. Considering the circumstances, this was a workable solution but only so long as his division commanders encountered no major difficulties.
U.S. intelligence had been squabbling over a possible PAVN cross-DMZ attack, during the months preceding the offensive. DIA analysts "cautiously" predicted such a contingency, while the CIA downplayed the possibility. General Lam's American advisors agreed with his assessment, that a blatant North Vietnamese violation of the Geneva Accord was unlikely. When the weekend of Easter 1972 arrived, General Giai had planned to rotate the operational areas of his 56th Regiment (along the central DMZ) with the 2nd Regiment (around the artillery base at Camp Carroll in the west). Because of a truck shortage, the units were moved simultaneously and became hopelessly intermixed and disorganized. At 11:30 on 30 March, both unit headquarters shut down their radios, for the exchange of operational areas. With communications fragmented, its units entangled and the weather bad enough to prevent aerial operations, the 3rd Division offered the massed PAVN forces to the north an irresistible target.