The Division guarded Highway 4, the major rice supply route to the Mekong Delta, and protected the roads and towns of Tây Ninh, Hậu Nghĩa and Long An Provinces (with a total of fourteen districts).

American advisers at Military Assistance Command, Vietnam (MACV) and in the field were puzzled and angry, blaming Chinh's lack of aggressiveness.

[4]: 47–8  The Corps senior US adviser had requested Chinh's immediate relief, but COMUSMACV General William Westmoreland chose not to press the matter, hoping that combined operations with American forces "will be able to develop the unit."

Under their protection, the two divisions performed static security missions, but rather than using this respite to regroup and retrain their forces, or to hunt down the local VC, the Vietnamese commanders had let their units degenerate through inactivity, and US advisers now rated them lower than even the neighboring RF/PF.

[4]: 188–91 From 19 to 21 June 1967 the 46th Regiment participated in Operation Concordia with the US Mobile Riverine Force against the VC 5th Nha Be Battalion in Cần Giuộc District of the Mekong Delta.

[4]: 245 From 11 March to 7 April 1968 the Division participated in Operation Quyet Thang to reestablish South Vietnamese control over the areas immediately around Saigon in the aftermath of the Tet Offensive.

[7]: 460–1  On 12 March, Troop M, 3rd Squadron, 11th ACR and a Regional Force company engaged more than 100 VC from the 267th and 269th Battalions in forest 6 km (3.7 mi) north of Đức Hòa in eastern Hậu Nghĩa Province.

[7]: 462  From 15 to 17 March the 3rd Squadron, 11th ACR and ARVN forces engaged the 272nd Regiment between Đức Hòa and Củ Chi, killing 273 VC before losing contact.

[7]: 464–6 In June 1969 the new II Field Force, Vietnam commander Lieutenant general Julian Ewell initiated the Dong Tien (or "Progress Together") Program with III Corps commander, General Đỗ Cao Trí, to "buddy up US and ARVN units to conduct combined operations [that would]... maximize the effectiveness of both forces [and] achieve in 2, 3, or 4 months a quantum jump in ARVN and RF/PF performance."

During this period most of the combined operations were small-scale affairs routine patrols, night ambushes, and an occasional skirmish with enemy local units that had stayed behind trying to keep the VC political infrastructure alive.

Nevertheless, the program was judged a success and, although moving the participating brigade back to the border region early in 1970, encouraged similar efforts with South Vietnamese airborne, territorial and CIDG forces around Tây Ninh city.

[8] On 30 April 1970 as part of Operation Toan Thang 42 (Total Victory), an early phase of the Cambodian Campaign, a Division regiment and the 10th Armored Cavalry Squadron together with other ARVN forces crossed into the Parrot's Beak region of Svay Rieng Province.

The 271st Independent Regiment was probably close to the Vàm Cỏ Đông River south of Go Dau Ha (11°06′43″N 106°09′11″E / 11.112°N 106.153°E / 11.112; 106.153) in Hậu Nghĩa Province, posing a threat to Highways 1 and 22, the line of communication between Saigon and Tây Ninh.

A successful crossing of the Thi Thien River below Bến Cát would isolate the 5th Division at Lai Khê, probably result in eliminating the defenses in front of the Bình Dương Province seat at Phú Cường, and place PAVN forces in a position for a rapid move into Saigon.

From the Parrot's Beak of Svay Rieng Province PAVN forces probed ARVN outposts along the Vàm Cỏ Đông River.

Since the port was the junction of National Routes 1 and 22, only 10 km (6.2 mi) from the Cambodian frontier, its loss would sever Tây Ninh and isolate sizable South Vietnamese forces there.

The PAVN exerted strong pressure against the Tây Ninh-Saigon corridor from its forward combat bases along the Saigon River from the Michelin Plantation to the Ho Bo Woods.

Principal targets for PAVN artillery and mortar attacks were Khiem Hanh, a forward base protecting the northern approach to Go Dau Ha; Trảng Bàng a principal town and defensive position astride Highway 1 midway between Tây Ninh City and Saigon; Củ Chi, the main base of the Division; and the defensive position at Trung Lap north of Highway 1.

[10]: 101–5 In early December 1974 heavy combat in Tây Ninh began, with PAVN rockets falling on the province capital and on adjacent military installations.

The PAVN attacked early on 7 December, by noon forces from the 205th Independent Regiment were in the hamlets, although the RF post at Soui Da held on.

Finally on 6 January 1975, without food and water and with nearly all ammunition expended, the 3rd Company, 314th RF Battalion picked up its wounded and withdrew down the mountain to friendly lines.

Aided by the excellent observation that Nui Ba Den afforded, PAVN artillery continued to shell Tây Ninh City with heavy rockets and 130 mm guns until the end of the month when the center was virtually deserted.

Faced by a formidable enemy on his western flank as he assumed command in II Corps, General Nguyễn Văn Toàn set about making decisive changes in dispositions and concepts to deal with the threat.

To make the Division, which covered an immense front from the Cambodian frontier nearly to the western outskirts of Saigon, more mobile, he gave responsibility for all static posts to Tây Ninh Regional Forces.

The Province chief reacted by sending two RF battalions east along Route 239 toward Bến Củi, but they were stopped by heavy fire short of the lost outpost.

With Tri Tam in its possession, the PAVN now controlled the Saigon River corridor from its beginning, near Tong Le Chon, to the ARVN outpost at Rach Bap in the Iron Triangle.

Khiem Hanh's principal mission was to prevent major PAVN units from closing on Routes 22 or 1 near the critical river port and road junction at Go Dau Ha.

When two large concentrations of tanks were sighted west of Go Dau Ha on 12 March, RVNAF fighter-bombers destroyed eight and damaged nine, losing three aircraft in the engagement.

[10]: 165–7 The 3rd Battalion, 48th Regiment made contact with a PAVN company west of the Vàm Cỏ Đông River on 17 March, killed 36, and captured a number of weapons.

As a precaution against being flanked by a strong attack down the Saigon River corridor, General Toàn sent the 2nd Battalion, 7th Regiment, to reinforce Rach Bap, the western anchor of the Iron Triangle.