Five years after joining the army as an enlisted man, he was promoted to Officer of Materials for the 2nd Battalion of the 19th Colonial Infantry Regiment (Officier du Matériel, II/19e RMIC) stationed in Móng Cái.
On March 9, 1945, as part of their coup d'état in French Indochina, Imperial Japanese Army forces in Tonkin attacked two battalions of the 19ème RMIC at Hà Cối.
During this period, he secretly made contacts with several Việt Quốc revolutionaries-in-exile most of whom would become his good friends and ardent supporters throughout his career in South Vietnam.
His abilities in organizing intelligence networks eventually landed him a position working for the Governor of North Vietnam, Nghiêm Xuân Thiện as Sous-Directeur des Etudes (Phó Sở Nghiên Cứu) where he reported to Captain Sylvain Trần Văn Minh.
In 1950, the State of Vietnam's Minister of Defense Phan Huy Quát, a Đại Việt leader, asked Đổng to join the Vietnamese National Army.
In late November, using 3 battle-hardened divisions (308th, 316th and 320th) General Giap attacked Nà Sản with the intention of defeating the French Union forces to take control of northwest Tonkin.
To put an end to the "human wave", Đổng ordered his artillery-support to level and to fire howitzers loaded with fragmentation shells directly at the enemy troops.
By the end of the year, he took command of the 2e Groupe Mobile that participated in some of the hardest-fought battles to pacify the Red River Delta, especially in the Ninh Bình area during Operation Hautes Alpes in March 1953.
The latter position was very important, for he was in command of nineteen light infantry battalions (TĐKQ) and three artillery companies with the mission to pacify a military zone comprising seven provinces.
The operation was successful, though the cost was high: one of Đổng light battalions at Quần Phương Hạ was completely destroyed by the Việt Minh's more seasoned independent regiments.
He would remain in charge of the coastal zone until October 25, 1956, when President Diệm transferred him to Sông Mao (Bình Thuận) to command the 3rd Field Division, a unit made up entirely of Nùng soldiers.
Lieutenant Colonel Đỗ Mậu, Đổng second-in-command who was Diệm's protégé and a Cần Lao party member, was promoted to replace him.
Colonel Đổng attracted Diệm's attention by refusing to let Cần Lao's cadres conduct political training sessions for his troops.
In 1959, some of the Nùng soldiers left the army to join Father Nguyễn Lạc Hoá, a good friend of Đổng and a fervent anti-communist priest at the newly formed Sea Swallows enclave in Cà Mau.
Most Vietnamese senior officers suspected that general Minh took US Ambassador Lodge's suggestion of eliminating the brothers "to prevent any colonel from bring them back to power".
After the coup, Colonel Đổng served briefly as 7th Infantry Division Commander, during which time he earned the alias "Tiger of the Delta" for his twelve successful operations against Viet Cong and NVA troops.
Tâm Châu stopped his anti-government activities after a meeting with General Nguyễn Khánh, while Trí Quang continued to cause political unrest.
Tâm Châu himself published a White Paper in 1993 accusing Trí Quang of being a power-hunger man manipulated by North Vietnam and of harboring Communist agents.
A declassified French Sûreté report showed that Trí Quang joined the Indochinese Communist Party in 1949, a fact that former SRV Deputy Prime Minister Tố Hữu proudly confirmed in 2000.
The monk cited the general's unexplained actions toward some of Diệm's people as evidences, such as: protecting Lê Văn "White" Thái (Dr. Tuyến's assistant), or defending Trần Quốc Bửu (co-founder of the Cần Lao party) and Mã Tuyên (Head of the Triều Châu Chinese in Saigon).
He also continued to serve armed forces personnel by co-founding an association for ancient and current combatants, the Hiệp Hội Chiến Sĩ Tự Do.
In particular, Ohio State University sent professors to train teachers and to teach QGNT's students in three special courses: typing, accounting and home economics.
Minister Đổng, with his own private army and considered by Thiệu as a potential threat, was dismissed from the cabinet in February 1974 and two months later imprisoned without trial on corruption charges.
Still, Đổng was only released in July after Trần Quốc Bửu, head of the Tổng Liên Đoàn Lao Công (Confederation of Vietnamese Labor, the equivalent of the American AFL-CIO), and Father Hoàng Quỳnh of the Northern Catholics pressured Thiệu to do so.
After his release, General Đổng spent his time mentoring senior Army officers and advising civilian opposition leaders on tactics against President Thiệu.
After coming to the United States and settling in Arlington County, Virginia, Đổng would occasionally serve as a translator on special projects for the Defense Department before retiring in 1982 to take care of his wife who had suffered from a stroke.