In 1972, he was made the commander of I Corps after incompetent leadership by General Hoàng Xuân Lãm resulted in a South Vietnamese collapse in the face of the Easter Offensive, a massive conventional invasion by North Vietnam.

[1] After graduating from Đà Lạt, he soon saw action in a 1955 operation to eliminate the Bình Xuyên river pirates who were vying with President Diệm's government for control of Saigon and the surrounding area.

He led a heliborne assault into Đỗ Xá Secret Zone in Minh Long District, Quảng Ngãi Province, in central Vietnam.

In 1965, Trưởng led the 5th Airborne Battalion on a helicopter assault into the Hát Dịch Secret Zone in the vicinity of the Ong Trinh Mountain in Phước Tuy Province southeast of Saigon, the base area of the VC 7th Division.

In two days of fighting, Trưởng's 5th Battalion inflicted heavy casualties on two VC regiments, and he was awarded a battlefield promotion to lieutenant colonel and the National Defense Medal, Fourth Class.

[3] Trưởng was asked to quell the rebellious 1st Division in Huế, which had decided to stop military operations against the VC in solidarity with the Buddhist protest movement.

Unlike most, he eschewed politics in choosing his officers,[6] and implemented new training programs to improve the capability of his troops and Regional (RF) and Popular Forces (PF) that augmented them.

[7] In 1967, Trưởng's 1st Division assaulted and dismantled the VC infrastructure and a large part of their fighters from the Luong Co-Dong Xuyen-My Xa Front in Hương Trà District in Thừa Thiên-Huế Province.

[1] During the Tết Offensive, Trưởng led the 1st Division in the Battle of Huế as the People's Army of Vietnam (PAVN) and VC were expelled from the old imperial city after three weeks of bitter street fighting.

[1] During his tenure in the Mekong Delta, Trưởng established a system of outposts along the border with Cambodia to block infiltration of PAVN/VC personnel and supplies into the region.

[10] During his period in charge of IV Corps, the region's regular forces were depleted because a proportion of them were across the border as part of the Cambodian Campaign,[11] seeking to destroy PAVN/VC jungle bases, supplies and staging grounds for an invasion into South Vietnam.

[11] In the forests surrounding U Minh, Trưởng's outpost building programs resulted in a record number of defectors as the populace became more confident in his forces' ability to provide security.

General Trưởng held PAVN forces at bay before Huế and then launched (against the initial resistance of President Nguyễn Văn Thiệu and MACV) Operation Lam Son 72.

During the counteroffensive, he successfully pushed PAVN forces back to the city of Quang Tri (which was retaken in September) and advanced on to the Cửa Việt river.

[1] Trưởng remained in command of I Corps until the collapse of South Vietnam, when the north of the country lapsed into anarchy amid confused leadership by President Thiệu.

That evening Trưởng ordered a retreat to a new defense line at the Mỹ Chánh River to defend Huế,[25] thereby ceding all of Quảng Trị Province.

[28] The South Vietnamese tried to evacuate from the other urban enclaves into Đà Nẵng, but the 1st Division collapsed after its commander, Brigadier General Nguyễn Văn Điềm, angered by Thiệu's abandonment, told his men, "We've been betrayed ...

[30][31] As anarchy and looting enveloped Đà Nẵng, and a defense of the city becoming impossible, Trưởng requested permission to evacuate by sea, but Thiệu, baffled, refused to make a decision.

"[1] In 1966, Trưởng's American adviser wrote to General Harold K. Johnson, describing the Vietnamese officer as "dedicated, humble, imaginative and tactically sound.

"[46] General Norman Schwarzkopf, who commanded US forces during the Gulf War against Iraq in 1991, served as Trưởng's adviser in the 1960s when he was deployed to South Vietnam as a major during a campaign at Ia Drang.

He wrote in his autobiography It Doesn't Take A Hero, that Trưởng "did not look like my idea of a military genius: only five feet seven ... very skinny, with hunched shoulders and a head that seemed too big for his body ... His face was pinched and intense ... and there was always a cigarette hanging from his lips.

Schwarzkopf said that Trưởng was "the most brilliant tactical commander I'd ever known" and that "by visualizing the terrain and drawing on his experience fighting the enemy for fifteen years, Truong showed an uncanny ability to predict what they were going to do".

[1][44] Lieutenant Colonel James H. Willbanks, who served in Vietnam and was a professor of military history at the United States Army Command and General Staff College, said of Trưởng: A humble man, Truong was an unselfish individual devoted to his profession.

[1]Unlike some South Vietnamese generals who had grown rich as they ascended the ranks, Trưởng was regarded as being completely incorruptible and lived a "spartan and ascetic" life.

According to Lieutenant General Cushman, Trưởng did not own a suit, and by the time he was appointed to command IV Corps, his wife tended to pigs, which were kept behind his basic living quarters in the headquarters at Cần Thơ.

General Bruce Palmer Jr., said Trưởng "deserved a better fate" than the mauling of his soldiers amid Thiệu's confused orders and the collapse of South Vietnam.