The offensive was designed to achieve a decisive victory, which even if it did not lead to the collapse of South Vietnam, would greatly improve the North's negotiating position at the Paris Peace Accords.

This first attempt by North Vietnam to invade the south since the Tet Offensive of 1968, became characterized by conventional infantry–armor assaults backed by heavy artillery, with both sides fielding the latest in technological advances in weapons systems.

In the I Corps Tactical Zone, North Vietnamese forces overran the ARVN’s defensive positions in a month-long battle and captured Quảng Trị city, before moving south in an attempt to seize Huế.

The PAVN similarly eliminated frontier defense forces in the II Corps Tactical Zone and advanced towards the provincial capital of Kon Tum, threatening to open a way to the sea, which would have split South Vietnam in two.

The campaign can be divided into three phases: April was a month of PAVN advances; May became a period of equilibrium; in June and July the South Vietnamese forces counter-attacked, culminating in the recapture of Quảng Trị City in September.

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.

"[15] 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.

[19] 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.

He notified Admiral Thomas Moorer, the 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.

[35] 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.

Significantly, allied intelligence had failed to predict both the scale of the offensive and the method of attack, giving PAVN "the inestimable benefit of shock effect, a crucial psychological edge over defenders who had expected something quite different.

The following morning, ARVN armoured elements held off a PAVN offensive briefly when the crucial Highway QL-1 bridge over the Cửa Việt River at Đông Hà was blown up by Capt.

Simultaneously, the 324B Division moved out of the A Sầu Valley and advanced directly eastward toward Fire Bases Bastogne and Checkmate, which protected the old imperial capital of Huế from the west.

[Note 5] PAVN advance elements were soon followed by anti-aircraft units armed with new ZSU-57-2 tracked weapon platforms and man-portable, shoulder-fired Grail missiles, which made low-level bombing attacks hazardous.

On 21 April, Abrams notified the U.S. Secretary of Defense that In summary...the pressure is mounting and the battle has become brutal...the senior military leadership has begun to bend and in some cases to break.

[38]: 92–4 By mid-May, Trưởng felt strong enough to go on the offensive in a series of limited attacks, feints, and raids codenamed Song Than (Tsunami) that were planned to throw the North Vietnamese off balance, enlarge the defensive perimeter around Huế, and deny the enemy time and space to maneuver.

The ARVN assault bogged down in the outskirts and the North Vietnamese, apprised of the plans for the offensive, moved the 304th and 308th Divisions to the west to avoid the U.S. airpower that was about to be unleashed upon Quảng Trị.

Trưởng's forces then advanced to the southern bank of the Thach Han River, where they halted, exhausted and depleted by heavy casualties and unable to push on to Đông Hà.

Sensing that the provincial capital of An Lộc would be the next target, the III Corps commander, Lieutenant General Nguyễn Văn Minh dispatched the 5th Division to hold the town.

PAVN forces advanced on the town through a deluge of rockets, bombs, and napalm delivered by U.S. and South Vietnamese aircraft supported by massed artillery, tank, and small arms fire.

Colonel William Miller, the senior U.S. advisor, was not happy with General Hung's continuous reluctance to launch counterattacks and his reliance on U.S. air power to defeat the North Vietnamese.

The initial shock of ARVN troops instilled by North Vietnamese armor was soon abated when they discovered that, because the supporting infantry failed to advance with the tanks, they became easy prey for anti-tank weapons.

Resupply was accomplished, however, by 448 aerial missions which managed to deliver 2,693 tons of air-dropped food, medical supplies, and ammunition,[74] supported by the US Army's "549th QM (AD/Airborne)" (QuarterMaster, Air Delivery/Airborne) Rigger Company, which had been rapid-deployed from Okinawa in early April.

It had become evident as early as January that the North Vietnamese were building up for offensive operations in the tri-border region and numerous B-52 strikes had been conducted in the area in hopes of slowing the build-up.

ARVN forces had also been deployed forward toward the border in order to slow the PAVN advance and allow the application of airpower to deplete North Vietnamese manpower and logistics.

"[85] To counter the possible threat from the west, Du had deployed two regiments of the 22nd Division to Tân Cảnh and Đắk Tô Base Camp and two armored squadrons to Ben Het.

[Note 11] Vann then used massive B-52 strikes to hold the North Vietnamese at arm's length and reduce their numbers while he managed to find additional troops with which to stabilize the situation.

[111] The weather conditions made early ground support haphazard, and these difficulties were compounded by North Vietnamese anti-aircraft units, which advanced behind the front line elements.

Nixon had taken a gamble that the Soviet Union, with which he was conducting negotiations for a strategic arms limitation treaty (SALT I), would withhold a negative reaction in return for improved relations with the West.

Combined with these strategic errors, PAVN commanders had also thrown away their local numerical superiority by making frontal attacks into heavy defensive fire and suffered massive casualties as a consequence.