On February 19, 1965, some units of the Army of the Republic of Vietnam commanded by General Lm Vn Pht and Colonel Phm Ngc Tho launched a coup against General Nguyn Khnh, the head of South Vietnam's ruling military junta. Their aim was to install General Trn Thin Khim, a Khnh rival who had been sent to Washington D.C. as Ambassador to the United States to prevent him from seizing power. The attempted coup reached a stalemate, and although the trio did not take power, a group of officers led by General Nguyn Chnh Thi and Air Marshal Nguyn Cao K, and hostile to both the plot and to Khnh himself, were able to force a leadership change and take control themselves with the support of American officials, who had lost confidence in Khnh.

Although Khnh had seized power in January 1964 in alliance with Khim, the pair had soon fallen out over policy disputes along religious lines, and the Catholic Khim began to plot against Khnh. Khim was believed to have helped plan a failed coup in September 1964, and Khnh exiled him as a result. While in Washington, Khim continued to plot alongside his aide Tho, who was actually a communist agent bent on trying to foment infighting at every opportunity. Aware of Tho's plans, Khnh summoned him back to Vietnam in an apparent attempt to capture him, and Tho responded by going into hiding and preparing for his attack. In the meantime, Khnh's hold on power was slipping as his military support dwindled, and he became increasingly reliant on the support of civilian Buddhist activists who favored negotiations with the communists and opposed escalation of the Vietnam War. The Americansmost notably Ambassador Maxwell Taylorwere opposed to this and had been lobbying various senior Vietnamese officers such as K to overthrow Khnh, who knew that American-sponsored moves to depose him were afoot.

However, the Americans were not counting on Tho and his fellow Catholic Pht trying to seize power on an explicitly religious platform, claiming fidelity to slain former Catholic President Ng nh Dim and promising to recall Khim from the US to lead the new regime. This caused alarm among the Buddhist majority, who had campaigned heavily against Dim's discriminatory religious policies in the months leading up to his ouster in November 1963. Although they wanted Khnh gone, the Americans did not want Tho and Pht to succeed, so they sought out K and Thi in an attempt to have them defeat the original coup and then depose Khnh. During the initial attack, Tho and Pht tried to capture both Khnh and K, but both men escaped narrowly, although some of their colleagues in the Armed Forces Council were arrested. Although the rebels were able to take control of Tan Son Nhut Air Base, the largest in the country and the military headquarters of South Vietnam, K was able to regroup quickly and retain control of the nearby Bien Hoa Air Base, using it to mobilize air power and stop the rebel advance with threats of bombing. Late in the night, Tho and Pht met K in a meeting arranged by the Americans, where an agreement was reached for the coup to be ended in return for Khnh's ouster. By early next morning, the bloodless military action was over as Tho and Pht went into hiding, and the junta voted to sack their leader Khnh, who was absent on a military inspection tour, thinking that K and Thi were on his side.

When Khnh heard of his ouster, he declared it to be illegal. After defying his colleagues and travelling around the country for a day in a fruitless attempt to rally support for a comeback, Khnh went into exile after being named to fill the meaningless post of Ambassador-at-Large and allowed an elaborate ceremonial military send-off to save face. Pht and Tho were later sentenced to death in absentia. Tho was hunted down and killed in July 1965, while Pht remained on the run for several years before turning himself in and being pardoned.

Colonel Phạm Ngọc Thảo (IPA: Hanoi: [fâˀm ŋoˀk tʰa᷉ɔ], Saigon: [fə̂ˀm ŋoˀk tʰə᷉ɔ]), also known as Albert Thảo (14 February 1922 – 17 July 1965), was a communist sleeper agent of the Viet Minh (and, later, of the Vietnam People's Army) who infiltrated the Army of the Republic of Vietnam and also became a major provincial leader in South Vietnam. In 1962, he was made overseer of Ngô Đình Nhu's Strategic Hamlet Program in South Vietnam and deliberately forced it forward at an unsustainable speed, causing the production of poorly equipped and poorly defended villages and the growth of rural resentment toward the regime of President Ngô Đình Diệm, Nhu's elder brother. In light of the failed land reform efforts in North Vietnam, the Hanoi government welcomed Thao's efforts to undermine Diem.

During the First Indochina War, Thảo was a communist officer in the Vietminh and helped oversee various operations in the Mekong Delta in the far south, at one point commanding his future enemy Nguyễn Khánh, who briefly served the communist cause. After the French withdrawal and the partition of Vietnam, Thảo stayed in the south and made a show of renouncing communism. He became part of the military establishment in the anti-communist southern regime and quickly rose through the ranks. Nominally Catholic, Thảo befriended Diệm's elder brother, Archbishop Pierre Martin Ngô Đình Thục—the devoutly Roman Catholic Ngô family strongly favored co-religionists and had great trust in Thảo, unaware that he was still loyal to the communists. He went on to serve as the chief of Bến Tre Province, and gained fame after the area—traditionally a communist stronghold—suddenly became peaceful and prosperous. Vietnamese and US officials, as well as journalists hostile to or supportive of Saigon, misinterpreted this as a testament to Thảo's great ability, and he was promoted to a more powerful position where he could further his sabotage. Thảo and the communists in the local area had simply stopped fighting, so that the communists could quietly recuperate, while Thảo would appear to be very skillful and be given a more important job where he could do more damage.Through intrigue, Thảo also helped destabilise and ultimately unseat two South Vietnamese regimes—Diem's and the military junta of Khánh. As the Diệm regime began to unravel in 1963, Thảo was one of the officers planning a coup. His plot was ultimately integrated into the successful plot and his activities promoted infighting which weakened the government and distracted the military from fighting the Viet Cong insurgency. Throughout 1964 and 1965, as South Vietnam was struggling to establish a stable state after the ouster of Diệm, Thảo was involved in several intrigues and coup plots which diverted the government from implementing its programs. In 1965, he went into hiding after a failed attempt to seize power from Khánh and was sentenced to death in absentia. Although this coup also failed, the subsequent chaos forced Khánh's junta to collapse. Thảo died the same year he was forced into hiding; it is believed that he was murdered after a bounty was placed on his head. After Vietnam was reunified at the end of the Vietnam War, the victorious communists claimed Thảo as one of their own and posthumously made him a one-star general.