Army of the Republic of Vietnam (ARVN) influence extended south to the Nông Sơn coal mines in the narrow canyon of the Sông Thu Bồn, about 10 kilometers from the district seat.
Also located in the valley was the 4th Company, 146th RF Battalion, which had its 80-man garrison in the Ap Ba hamlet group (15°41′48″N 108°07′19″E / 15.6966°N 108.122°E / 15.6966; 108.122), along the road that twisted eastward over the Deo Le Pass to Quế Sơn.
The strength of the 3rd Battalion, 56th Infantry, was only about 360 men, but its 2nd Company was not in the camp; rather, it had set up outposts on two hills along the east bank of the Sông Thu Bồn.
One rifle platoon was on Cua Tan Mountain(15°42′07″N 108°02′37″E / 15.7019°N 108.0437°E / 15.7019; 108.0437) directly across the river from Da Trach, and the rest of the company was at Khuong Que (15°43′26″N 108°03′47″E / 15.7238°N 108.063°E / 15.7238; 108.063), to the north.
[1]: 114–5 Shortly after midnight on 18 July, PAVN artillery, rockets and mortar rounds began exploding on the defenses and outposts of Da Trach.
[1]: 115 Simultaneously with their assault on Da Trach, the PAVN began the Battle of Thượng Đức to the northwest, stretching the ARVN forces in the area.
At mid-afternoon, the five-battalion PAVN assault, which by this time included the 10th Sapper Battalion against the northern sector, had carried through the southwest defense line.
His staff went to work immediately drafting the tactical plan for Quang Trung 4/74 with the objective of retaking Da Trach.
A salvo of 35 122 mm rockets fell on Da Nang Air Base, damage to RVNAF operations was slight, although 16 people died and over 70 were wounded many of whom were civilians and military dependents.
Meanwhile, north of Đại Lộc on Route 540, the 370th RF Company repulsed a strong enemy attempt to interdict the ARVN line of communication, killing 30 of the attackers and capturing many weapons.
The feasibility of the plan came into question, however, when the last contact with the Da Trach defenders on 19 July revealed that the command group and two companies of the 78th Rangers were under heavy attack on the hill at Cua Tan.
By the afternoon of 19 July, the 1st Battalion, 2nd Infantry was in contact with elements of the PAVN 36th Regiment on Ky Vi Mountain and on Hill 238 (15°44′56″N 108°06′47″E / 15.749°N 108.113°E / 15.749; 108.113), to the west.
The RVNAF flew 18 attack sorties in support, killing 75 PAVN infantrymen and destroying a mortar, but the ARVN advance had to be halted.
Suspecting a trap in the Khe Le Valley, Hinh ordered the 2nd Infantry to stop and sent reconnaissance patrols forward.
[1]: 116 By 22 July, the PAVN command at Da Trach apparently realised that the ARVN 2nd Infantry Regiment was not advancing into the trap in the Khe Le Valley.
Seeing a disaster in the making for the 2nd Infantry, Hinh had his division reconnaissance company lifted in by helicopter to help defend the command post.
Reaching the command post late in the afternoon, the reconnaissance company was soon joined by the 37th Ranger Battalion and two troops of the 11th Armored Cavalry which Hinh had sent overland to reinforce the beleaguered 2nd Infantry.
The PAVN plans for the 38th Regiment to move east into Go Noi were upset by the rapid ARVN deployment of the 12th Ranger Group.
The battered 1st Regiment was no longer equipped to protect the rear of the 38th or its line of communication against the expected counterattacks of the three Ranger battalions of the 12th Group.
[1]: 117 The 54th Infantry Regiment, arrived in Quảng Nam on 26 July, put its headquarters at Điện Bàn District Town and immediately went into action.
The 1st Air Division flew 67 sorties on the 25th and 57 on the 26th, destroying a tank and several antiaircraft and mortar positions, striking large troop concentrations, and killing about 90 PAVN soldiers.
Although they inflicted heavy casualties on the PAVN 36th Regiment, the Rangers were forced back about 1,000 meters to the slopes of Nui Duong Coi.
The PAVN pursued, and fighting continued in the rough terrain in front of Nui Duong Coi for several days.
The RVNAF contributed greatly to the ARVN success; although Ranger casualties were high, more than 35 killed, 100 wounded, and 25 missing, the PAVN left over 200 dead on the field.
[1]: 120 In September, faced with a deteriorating situation north of the Hải Vân Pass, Trưởng ordered the 54th Infantry to return to the 1st Division.
While mortar and artillery fire pounded the 3rd Battalion command post, PAVN sappers entered the headquarters perimeter and severed communications with the two forward ARVN companies.
[1]: 120 The PAVN 1st Regiment had accomplished its mission, but casualties were heavy, and it lacked the strength either to pursue or to consolidate its gains.
[1]: 121 This article incorporates public domain material from websites or documents of the United States Army Center of Military History.