The Hải Vân Ridge formed the Thừa Thiên-Quảng Nam Province boundary from the sea to Bạch Mã Mountain, which was occupied by the People's Army of Vietnam (PAVN) in October 1973.
[1]: 125 At first, the I Corps commander, General Ngô Quang Trưởng, viewed the see-saw contest for the hills south of Núi Mô Tau as hardly more than training exercises and of no lasting tactical or strategic importance.
[1] In early June 1974, after releasing the 1st Airborne Brigade to the reserve controlled by the Joint General Staff, Trưởng made major adjustments in command and deployments north of the Hải Vân Pass.
The division commander, Brigadier General Bui The Lan, positioned his forces with the 258th Marine Brigade, with one M48 tank company attached, defending from the sea southwest to about 5 km (3.1 mi) east of Quảng Trị.
[1]: 129 On 29 June Trưởng directed his deputy north of the Hải Vân Pass, General Lâm Quang Thi, to constitute a regimental reserve for the expected PAVN counterattacks against the newly won hills.
The 1st Division, with only three regiments, was left with a 60 km (37 mi) front including Highway 1 and no reserve north of the Hải Vân Pass.
Since this situation was hazardous, on 3 August Trưởng ordered Thi to reconstitute a reserve using the 15th Ranger Group, at that time attached to the Marine Division on the Thạch Hãn River.
However Thi was still without a reserve north of the Hải Vân Pass and fresh opportunities for the new PAVN 2nd Corps appeared in Phú Lộc District.
The PAVN 6th and 803rd Regiments lost nearly 300 men and over 100 weapons in these attacks, but the ARVN 3rd Infantry was no longer combat effective due to casualties and equipment losses.
[1]: 130 In an apparent diversion to draw ARVN forces northward away from Phú Lộc, the PAVN on 21 September strongly attacked the 5th and 8th Marine and the 61st Ranger Battalions holding the Phong Điền sector north of Huế.
Although some 6,600 rounds, including hundreds from 130 mm field guns, and heavy rockets, struck the defenses, the South Vietnamese held firmly against the ground attacks that followed.
Over 240 PAVN infantrymen from the 325th Division were killed, mostly by ARVN artillery, in front of the 8th Marines, and Thi made no deployments in response to the attack.
But the ARVN artillery was taking its toll of the PAVN defenders, who were also suffering the effects of cold rains sweeping across the steep, shell-tom slopes.
[1]: 130 As heavy rains continued, movement and fire support became increasingly difficult, and the ARVN offensive in southern Thừa Thiên slowed considerably.
For a new assault on Núi Mô Tau, Trưởng authorized the reinforcement of the 54th Infantry Regiment by the 15th Ranger Group drawn out of the Bo River Valley west of Huế; the 54th would make the main attack.
Weather was terrible that day, but two Ranger battalions made some progress and established contact with the PAVN on the eastern and southeastern slopes of the hill.
On 28 November, with good weather and long-awaited support from the RVNAF, the 1st Battalion, 54th Infantry, began moving toward the crest of Núi Mô Tau.
Intense fires drove the South Vietnamese back and although the 1st Infantry retained a foothold on the slopes, it was unable to carry the crest.
Furthermore, the PAVN 78th Artillery Regiment was forced to remove its batteries because resupply past the ARVN position around Núi Mô Tau became too difficult.
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, protected by antiaircraft weapons and supplied by newly improved roads.
The battered PAVN 324th Division withdrew to their base areas southwest of Phú Lộc to reorganize and await orders for the next campaign.
[3] This article incorporates public domain material from websites or documents of the United States Army Center of Military History.