Until late 1971 the division was also tasked with the defence of Quảng Trị, the closest town to the Vietnamese Demilitarized Zone (VDMZ) and among the first to be hit by the Tet Offensive.

[1] On 29 May 1965 in the Battle of Ba Gia the Division's 1st Battalion, 51st Regiment was ambushed by Vietcong (VC) as it attempted to relieve a South Vietnamese Regional Force (RF) unit in the village of Phuoc Loc.

By the beginning of April Struggle Movement forces appeared to control most of Huế, Da Nang and Hoi An and had the support of the I Corps headquarters and the division.

At the same time, South Vietnamese combat operations in the northern zone began to peter out, and the danger that the crisis presented to the war effort became evident.

Protected by Trưởng's forces, Loan's police removed the Buddhist altars and arrested most of the remaining leaders of the Struggle Movement, including Thích Trí Quang.

[8] In the early morning hours of 31 January 1968, a division-sized force of PAVN and VC soldiers launched a coordinated attack on the city of Huế breaking through the western wall of the Citadel.

Although the PAVN battalion penetrated the division compound, an ad hoc 200-man defensive force of staff officers and clerks staved off the enemy assaults.

[7]: 168  The 2nd ARVN Airborne Battalion reinforced the convoy, and the South Vietnamese finally penetrated the lines and entered the Citadel in the early morning hours of 1 February.

[7]: 168  The 2nd and 3rd Battalions, 3rd Regiment, advanced east from encampments southwest of the city along the northern bank of the Perfume River, but PAVN defensive fires forced them to fall back.

Trưởng then ordered the 2nd Battalion 3rd Regiment and the Black Panther Company to recapture the Imperial City and this was achieved against minimal resistance by late afternoon.

The last remaining pocket of PAVN at the southwest corner of the Citadel was eliminated in an attack by the 4th Vietnamese Marine Battalion in the early hours of 25 February.

The remnants of the 812th, having been hit hard by ARVN defenders and American air power and ground troops on the outskirts of the city, particularly artillery and helicopters,[9]: 56  broke up into small groups, sometimes mingling with crowds of fleeing refugees, and began to exfiltrate the area, trying to avoid further contact with Allied forces.

They attributed the decisive defeat to the hard-nosed South Vietnamese defense, effective intelligence on PAVN/VC movements and the air mobile tactics of the 1st Cavalry Division.

[10] On 28 April at the start of the May Offensive the Division's Hac Bao Company located the 8th Battalion, 90th Regiment in the fishing hamlet of Phuoc Yen 6 km northwest of Huế.

[7]: 292  On 30 April, a PAVN unit opened fire on a US Navy Clearwater patrol from entrenched positions near Dai Do, 2.5 km northeast of Đông Hà.

From 15 March to 2 May 1969 the 3rd Battalion, 2nd Regiment participated in Operation Maine Crag with the 3rd Marine Division in the "Vietnam Salient" in northwest Quảng Trị Province.

Another series of positions along the Ngoc Ke Trai fell in November as signs of deteriorating morale and weak leadership began to appear in the formerly highly respected division.

These were too much the results of conditions beyond the control of the commander: an extended front under continuous enemy pressure, the debilitating effects of cold, wet, typhoon weather; inadequate supply to the forward infantry outposts; and the worsening economic straits in which the soldiers found themselves.

[24]: 129–30 From 28 August to 10 December 1974 the 3rd and 51st Regiments together with the 15th Ranger Group fought the Battle of Phú Lộc forcing the PAVN back from hills overlooking Highway 1 and from which they could shell Phu Bai Air Base.

Reinforced PAVN battalions equipped with new weapons, ranks filling with fresh replacements from the north-were in close contact with ARVN outposts the length of the front.

Behind these battalions, new formations of tanks were being assembled and large logistical installations were being constructed, heavily protected by antiaircraft and supplied by newly improved roads.

[24]: 131 On the early morning of 8 March regiments of the PAVN 324B Division began the Thua Thien campaign attacking along an 8 km sector southeast of Huế.

[24]: 155 A battalion of the PAVN 6th Regiment infiltrated through Phú Lộc, and two of its companies seized 12 fishing boats, which ferried them across Dam Cau Hai Bay to Vinh Loc Island.

Trưởng and Thi anticipated a mass civilian exodus from Quảng Trị as soon as the people saw that the Marines were leaving, and he directed his staff to prepare plans to assist the refugees.

[24]: 157 On 19 March at meetings in Saigon with President Nguyễn Văn Thiệu, Trưởng was directed to stop the evacuation of Hue and to defend enclaves at Huế, Da Nang, Chu Lai and Quang Ngai City.

The Imperial City would be defended despite the fact that PAVN artillery had, on 19 March, already struck inside the Citadel and Highway 1 was clogged with the southbound traffic of thousands of refugees.

[24]: 158–9 On the morning of 21 March the lead battalions of the PAVN 324B and 325th Divisions, together with the independent Tri-Thien Regiment, with heavy artillery support, assaulted South Vietnamese positions from the Bo Corridor to Phú Lộc.

[24]: 159 On 23 March the 913th Regional Forces Group on the My Chanh Line north of Huế withdrew without orders and they refused to stop at the next delaying position near Phong Dien District Town.

By the time these orders were issued, what was left of the population of Hue was streaming toward Tân Mỹ Base to take any available boat or ship out of Thua Thien Province.

Trưởng flew over the column making its way down the long stretch of Vinh Loc Island and noted that the only apparent disciplined, cohesive units were marines.