Later during Vietnamization the Civilian Irregular Defense Group program was transferred from MACV and integrated as Border Battalions responsible for manning remote outposts in the Central Highlands.

[5] With improvements in the ARVN from 1969 onward and the growing prestige of the Airborne and Marine Division, depredation had caused the Central Highlands-based Rangers to become manned by deserters, released convicts and Montagnards[6] nevertheless the unit continued to operate in the Easter Offensive and frontier skirmishes in 1973 and 1974.

At 13:30 the Rangers walked into an ambush by the VC 70th Battalion which was overrun within 15 minutes, losing a third of their men, the remainder withdrew and established a defensive perimeter 1.2 km northwest and called for air support.

The 1st Regiment was prevented from reinforcing the Rangers by intensive small arms and mortar fire and Marine airstrikes hit the VC positions.

[12]: 276 During 1966, the battalions were formed into task forces, and five Ranger Group headquarters were created at Corps level to provide command and control for tactical operations.

[17]: 120–5 On 10 September 1967 the 37th Ranger Battalion encountered a PAVN force north of the Operation Swift area in the Quế Sơn Valley.

[18]: 269  In late February, ground sensors detected the PAVN 66th Regiment, 304th Division preparing to mount an attack on the positions of the 37th Ranger Battalion on the eastern perimeter of the base.

[18]: 281 During the Tet Offensive battle of Cholon and Phu Tho Racetrack from 31 January-11 February 1968 the 30th, 33rd and 38th Ranger Battalions were all involved in the fighting.

[19]: 346–7 In the mopping up operations of the Battle of Hue on 25 February a two Battalion Ranger task force recaptured the Gia Hoi sector (16°28′34″N 107°35′20″E / 16.476°N 107.589°E / 16.476; 107.589) between the east wall of the Huế Citadel and the Perfume River.

[20]: 26  On 10 May the 33rd Rangers swept the area around Phú Thọ Racetrack finding 9 VC dead and various weapons and supplies.

[20]: 25–7 On 31 August during the Phase III Offensive south of Da Nang the 21st and 37th Ranger Battalions trapped a PAVN unit in a bend of the Song Ky Lam River with the 3rd Battalion, 5th Marines on the opposite bank killing 80 PAVN with 1 captured for the loss of 7 ARVN dead and 45 wounded.

At 20:00 Company H 2/5th Marines ambushed 30 PAVN as they attempted to cross the Song Ky Lam on boats, killing all on board.

[18]: 382 From 7 December 1968 to 8 March 1969 the 1st Ranger Group participated in Operation Taylor Common with the US 1st Marine Division's Task Force Yankee in the An Hoa basin, Quảng Nam Province against the PAVN/VC Base Area 112.

[21]: 175–87 On 27 April 1970 a Ranger Battalion had advanced into Kandal Province, Cambodia to destroy a PAVN base in the first operation of the Cambodian Campaign[22]: 146  On 30 April, as part of Operation Toan Thang 42 (Total Victory) three Ranger battalions and other ARVN forces crossed into the Parrot's Beak region of Svay Rieng Province.

The two battalions developed firebases north and south of Route 9 in Laos to serve as tripwires for any PAVN advance into the zone of the ARVN incursion.

On 19 February the attacks commenced against Ranger North conducted by the 102nd Regiment, 308th Division supported by Soviet-built PT-76 and T-54 tanks.

Although more than 600 PAVN troops were estimated as killed during the action, casualties in the three-day fight totaled 75 percent of the ARVN battalion.

[26]: 86  On 21 April the PAVN launched an assault on Firebase Delta by 3 tanks supported by infantry and by the evening had succeeded in overrunning the base.

The PAVN bombarded the town and gradually reduced the defensive line, while all the time being battered by US and South Vietnamese airstrikes.

On 11 May the PAVN 5th and 9th Divisions launched a massive all-out infantry and armor assault on An Lộc, suffering severe losses to airstrikes but further squeezing the defenders.

On 21 May the 2nd and 6th Ranger Groups supported by armored cavalry and engineer elements began an operation to clear Route 14 from Pleiku to Kontum which had been blocked by the PAVN 95B Regiment near Chu Pao Mountain.

The attack was slowed by multiple PAVN ambushes and roadblocks and ultimately halted by the defenses at Chu Pao Mountain.

During the Battle of Tong Le Chon from 25 March 1973 to 12 April 1974 the 92nd Ranger Battalion at Tonle Cham Camp held out against a prolonged PAVN siege before finally being overrun.

The 68th was driven from its dug-in positions on Hill 252 in the important Cong Hoa Valley approach to Quang Ngai City-in October by an inferior VC unit.

[30]: 63 From 30 October to 10 December 1973 the 21st Ranger Battalion together with the 23rd Division fought the Battle of Quang Duc, successfully defeating PAVN efforts to expand their logistical network from Cambodia.

[30]: 58–60 From 27 March 1974 the 83rd Ranger battalion held the Đức Huệ camp against attack by the PAVN 5th Division which began the Battle of Svay Rieng.

[30]: 113–21 From 28 August to 10 December 1974 the 15th Ranger Group together with the 3rd and 51st Regiments, 1st Division 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.

Ranger courses were established at three training sites in May 1960: Da Nang, Nha Trang, and Song Mao.

The original Nha Trang Training course relocated to Dục Mỹ in 1961 and would become the central Ranger-Biêt Dông Quân-Company and Battalion sized unit training was later established at Trung Lap; to ensure a consistently high level of combat readiness, BDQ units regularly rotated through both RTC's.

[34] Rangers wore a snarling black tiger superimposed over a large yellow star painted in front of their helmets.