Having abandoned the Communist-led Việt Minh resistance to join the Vietnamese National Army, the predecessor of the ARVN, Mau rose to be head of military security under Diệm.
He initially tried to organize a coup group himself with Colonel Phạm Ngọc Thảo, an undetected communist agent bent on maximising infighting, and disillusioned intelligence director Trần Kim Tuyến mainly consisting of mid-level officers.
Fearing his political skills, the leading generals tried to sideline him and placed him in the non-influential post of Information Minister, where he censored newspapers.
During the 1940s, Mậu had joined the Việt Minh resistance as a Battalion Commanding officer in the Central Vietnam, but became disillusioned by Communist cadres.
According to Ellen Hammer, there were "perhaps as many as six and possibly more" different plots,[6] and these spanned the gamut of society to include civilian politicians, union leaders, and university students.
[8][9] Another in the group was Colonel Phạm Ngọc Thảo, an undetected communist agent who was deliberately fomenting infighting among the officers and mismanaging the Strategic Hamlet Program in order to destabilize the Saigon government.
Despite his high rank, Minh was out of favour and served as the Presidential Military Advisor, a meaningless desk job where he had no subordinates in the field and no access to soldiers.
Mậu concocted military intelligence reports with false data claiming the Viet Cong (VC) was massing outside the capital for an offensive.
[25] The United States had cut off funding for the CIA-trained Special Forces because Diệm used them to stop coups, repress dissidents and attack Buddhist pagodas in the capital instead of combating the communists in rural areas.
[25] Mậu helped to organise a lunchtime meeting at Joint General Staff Headquarters and invited senior officers to the event.
[29] Mậu found himself on the opposite side to his nephew and Air Force Lieutenant Đỏ Thơ, Diệm's aide-de-camp.
[30] Late in the evening, Thơ accompanied the Ngô brothers as they escaped the rebel siege on Gia Long Palace and absconded to the home of a Chinese supporter in Cholon.
[33] After the coup was successfully completed, the media learned about the conspiracy organised by Tuyến and Thảo which was more advanced than that of the generals before being integrated into the main plot.
Đôn thought the younger officers had publicized their well-advanced plot in order to gain personal acclaim and distract attention from the generals' success, so he threatened to arrest them but Mậu intervened to protect them.
Saigon newspapers, which been able to operate liberally in the post-Diệm era, reported that the junta was paralysed because all twelve generals in the MRC had equal power.
[38] Disgruntled, Mậu began recruiting for a coup against Minh's MRC, sounding out exiles in Cambodia and France as well as those who had returned after the overthrow of Diệm.
[2] Khánh had long been regarded as an ambitious and unscrupulous officer by his colleagues,[40] and he had a reputation for switching sides in high-level disputes for personal gain.
[39][41] The most important link in Mậu's plan was Colonel Nguyễn Chánh Thi, the former paratroop commander who had fled to Cambodia in the wake of the failed 1960 coup attempt against Diệm.
[42] At the time, there was innuendo that some generals in the MRC would become neutralist and stop fighting the communists, and that they were plotting with French President Charles de Gaulle, who supported such a solution in order to remove the US presence.
[44][45] Khánh assumed control of a new junta, and Mậu was one three Deputy Prime Ministers, overseeing social and cultural affairs.