After operating for a short period just south of the Phu Bai tactical area of responsibility (TAOR), on 29 October it commenced Operation Pawnee III in Phú Lộc District, north of the strategic Hải Vân Pass, with the mission to keep Route 1 open between Da Nang and Phu Bai.

[3]: 101 On 16 January the battalion was moved by air to Khe Sanh Combat Base unifying the regiment for the first time in the war.

[3]: 716  On 28 July the battalion proceeded to Quang Tri Combat Base to prepare and train for service afloat with Special Landing Force (SLF) Alpha.

On 20 October the battalion again came ashore assuming responsibility for the security of Route 1 in the Hải Vân Pass and the Liên Chiểu Esso Depot (16°08′31″N 108°07′44″E / 16.142°N 108.129°E / 16.142; 108.129).

The battalion operated mostly in the steep, jungled mountains and left close-in protection of the road and railroad largely to the South Vietnamese Regional Force.

[5]: 32  As part of Operation Keystone Bluejay the regiment stood down for deactivation in late February to early March with the 1st Marines taking over most of their tactical area of responsibility.

[5]: 28  On 15 February elements of the 101st Airborne Division relieved the battalion companies stationed at Hill 88 and Lăng Cô Bridge.

On 1 March, the 3rd Battalion, 1st Marines relieved the remaining companies at the Liên Chiểu Esso Depot and the Hải Vân Pass.