[1]: 298 In the 1960 South Vietnamese coup attempt, the loyalist Colonel Nguyễn Văn Thiệu used the Division to storm into Saigon to save President Ngô Đình Diệm.
However, in the successful coup attempt of 1963, Thiệu rebelled and the Division along with the rest of the III Corps of Tôn Thất Đính, attacked Saigon.
The division was largely composed of Nùng people until about 1965 when its composition was increasingly ethnic Vietnamese and the Nùngs moved into MIKE Force units.
[3]: 339 The Division's US adviser reported that the commander, General Phạm Quốc Thuần, had "gone to pieces" over the mauling his 7th Regiment had received and the unit was notorious for its high desertion rate.
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.
Combined activities consisted of small unit patrolling, village seals and searches, propaganda campaigns, intelligence collection efforts, and various civic improvement projects.
In July, however, with the bulk of his units engaged in heavy fighting north of Saigon, DePuy had to abandon the combined operations task force concept.
Thereafter, DePuy monitored and supported the division's activities in Bình Dương Province through his 2nd Brigade headquarters, only occasionally assigning ground units to the effort.
[4]: 309–24 From 8–26 January 1967 4 battalions of the division participated in Operation Cedar Falls a large US search and destroy mission against the Iron Triangle, Bình Dương Province.
As CORDS would in-effect undermine the continual insurgency war, the PAVN 141st Regiment had launched a full-scale attack against the division HQ in hopes of quashing the experiment.
Although continually judged by American leaders as corrupt and incapable, Thuan had strong political ties with the Junta generals, in this case, Thiệu.
John Paul Vann noted the "widespread public belief that Thuan not only controlled most of the local bars and prostitution houses but also extorted protection fees for convoys moving through his Division tactical area.
Minor incidents, like Thuần's daily pot shots at birds from the second story balcony of his home and the subsequent accidental wounding of his intelligence adviser, were not uncommon and at times trivialized and mocked the entire war effort.
[2]: 333–4 In June 1969 the new II Field Force, Vietnam commander Lt. Gen. 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.
Since 1965 the American division had worked the area, driving the regular enemy units across the Cambodian border and slowly rooting out his larger local forces.
Such poor track records reflected what Americans derisively called Saigon's "search and avoid" tactics, and were patently unacceptable to Ewell and Trí.
At the same time, the projected redeployment of US forces from South Vietnam made it all the more necessary that Saigon bring units like the division back into the mainstream of the war effort as soon as possible.
Another significant factor, one that was both helpful and seductive, was the inactivity of PAVN/VC military forces, and thus, as in the other Dong Tien operations, there was no real test of South Vietnamese effectiveness in heavy fighting.
However, when the program terminated in March 1970, it had pried the 5th Division out of its safe havens in southern Bình Dương and oriented its soldiers away from the political and economic concerns of the Saigon metropolitan area.
[2]: 412–5 On 30 April 1970 as part of Operation Toan Thang 42 (Total Victory), an early phase of the Cambodian Campaign, a division infantry regiment and the 1st Armored Cavalry Squadron together with other ARVN forces crossed into the Parrot's Beak region of Svay Rieng Province.
Pushed by both Abrams and Minh to relieve him, Thiệu finally acceded and in April 1971 brought Col. Lê Văn Hưng up from Phong Dinh Province to take over the battered Division.
[8]: 47–9 The attack began around 06:50 on 5 April with a heavy barrage of artillery, rocket and mortar fire targeting the headquarters of the 9th Regiment and the Lộc Ninh district compound.
[9]: 46 A second ground assault in the afternoon was repelled by airstrikes however Vinh was either planning to surrender or desert when he ordered two of his soldiers to open the gates of the command compound at around 22:00.
[9]: 49 On the morning of 6 April a renewed VC assault entered the base and at this point the 9th Regiment only had 50 soldiers left, while another 150 wounded were in the hospital bunker.
In an attempt to save Lộc Ninh, Brigadier General Lê Văn Hưng ordered Task Force 52 to move north to reinforce the beleaguered 9th Regiment.
[10]: 19 On the afternoon of 6 April, the 3rd Battalion, 9th Regiment, along with the men of the 1st Cavalry Squadron at FSB Alpha who had refused to surrender arrived at Lộc Ninh to join the defense.
[9]: 50 At 07:00 on 7 April, the VC massed for another ground assault from the north and west of Lộc Ninh, with support from heavy artillery, tanks and armored personnel carriers.
Elements of the 7th Regiment defending the area were unable to hold off the VC, so they were ordered to destroy their equipment and join other ARVN units in the provincial capital.
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 air strikes but further squeezing the defenders.
In early September the division renewed the effort to recapture Base 82, with the 8th Infantry Regiment nearly succeeding until being routed by a PAVN armored counterattack with casualties of six killed, 29 missing and 67 wounded.