South Vietnam was in political chaos during much of the year, as generals competed for power and Buddhists protested against the government. The Viet Cong (VC) communist guerrillas expanded their operations and defeated the South Vietnamese Army of the Republic of Vietnam (ARVN) in many battles. North Vietnam made a definitive judgement in January to assist the VC insurgency with men and material. In November, North Vietnam ordered the People's Army of Vietnam (PAVN) to infiltrate units into South Vietnam and undertake joint military operations with the VC.
The new President of the United States, Lyndon Johnson, and his civilian and military advisers wrestled with the problem of a failing government in South Vietnam and military gains by the VC. In August, an attack on United States Navy vessels caused Johnson to seek and gain U.S. congressional approval of the Tonkin Gulf Resolution, which authorized him to use military force if necessary to defend South Vietnam. Throughout the year, there were calls from many quarters—American, foreign, and South Vietnamese—for the United States to negotiate an agreement for the neutralization of South Vietnam, which they refused to consider.
Many of Johnson's advisers advocated an air war against North Vietnam and the introduction of U.S. combat troops into South Vietnam. By year's end, the 23,000 U.S. military personnel in South Vietnam were still technically "advisers" (although they participated in many air and ground operations with the ARVN), but Johnson was contemplating U.S. ground troops.
January
United States Marine Corps (USMC) Major general Victor H. Krulak, along with a committee of experts asked to advise on the war, submitted a recommendation to President Johnson for a three phase series of covert actions against North Vietnam. Phase I, for February to May, called for propaganda dissemination and "20 destructive undertakings ... designed to result in substantial destruction, economic loss and harassment", and a second and third phase of increasing magnitude.
The ARVN captured a large arms cache in the Mekong Delta, including weapons manufactured in China. United States Secretary of State Dean Rusk said this proved that North Vietnam was supplying the VC.
A VC battalion massed near My Tinh An hamlet near the border with Định Tường province. The VC were soon surrounded by a Ranger company, two Civil Guard companies, and Self-Defense Corps elements. On the morning of the 5th the ARVN 8th Airborne Battalion supported by M113 armored personnel carriers attacked, but became bogged down. The Airborne withdrew and artillery and airstrikes hit the VC, with one airstrike accidentally hitting ARVN forces. By the morning of the 6th the VC had withdrawn leaving only one body, but radio intercepts and local villagers reported that the VC had evacuated about 100 corpses. The next day a shallow grave containing 41 VC dead was found. The ARVN lost ten killed and thirty-six wounded, with an M113 and seven aircraft damaged.
VC sappers destroyed 201,780 gallons of petroleum products in Vĩnh Long.
United States Ambassador to South Vietnam Henry Cabot Lodge Jr. reported to Washington that the new President of South Vietnam Dương Văn Minh told him that he opposed American soldiers going into villages and districts of rural Vietnam as they would be perceived as "more imperialistic than the French" and would give credence to communist propaganda that the Saigon government was a lackey of the United States.
Theodore Sorensen, one of former President John F. Kennedy's most trusted aides, wrote to Johnson to oppose the neutralization of South Vietnam as proposed by French President Charles de Gaulle and others. Sorensoen said neutralization would result in a communist takeover of South Vietnam, weaken the U.S. position in Asia, and cause political problems for the Democratic Party. Johnson's principal advisers—Dean Rusk, Robert McNamara, McGeorge Bundy and Walter Rostow—echoed Sorensen's views. In December, Senator Mike Mansfield had proposed negotiation of a neutral South Vietnam.
Lieutenant general William C. Westmoreland was appointed deputy commander of Military Assistance Command, Vietnam (MACV).
An ARVN company withdrawing from the operational area of Operation Dan Tam I in War Zone D was ambushed by approximately 500 VC of the D800 Battalion. Artillery support was called in, but after an hour the unit commander radioed that the VC had broken contact. When relief forces arrived, it was revealed that the commander had been forced to send a false message after the unit had been overrun. ARVN losses were six dead, 43 missing, and 34 wounded and more than 70 weapons lost. VC losses were two dead and one captured.
Operation Phuong Hoang I in Thạnh Phú district was initially met with heavy VC resistance. It resulted in 85 VC killed and 72 captured. ARVN losses were 15 killed and 40 wounded. US losses were four killed, six wounded, two missing, and two helicopters destroyed.
The Central Committee of the Communist Party of Vietnam adopted Resolution 9. The secret resolution declared all-out war on South Vietnam to defeat the ARVN before the United States could introduce a large number of American soldiers into the war. The Resolution estimated that American soldiers participating in the war would not exceed 100,000. The Americans "clearly understand that if they get bogged down in a large-scale protracted war, then they will fall into an extremely defensive position internationally." Diplomacy would be expanded to gain "the sympathy of antiwar groups in the United States" and other people around the world. Finally, the Resolution called for a purge of party members in North Vietnam who had emphasized socialistic development in North Vietnam rather than North Vietnamese help for the "liberation" of the South. Resolution 9 was the most important Communist party decision on action in South Vietnam since the Geneva Accords of 1954, which had provisionally separated North and South Vietnam pending national elections (never held, due to opposition by the government of South Vietnam).
With the adoption of Resolution 9, party moderates such as Ho Chi Minh and Võ Nguyên Giáp were marginalized and those who supported the Soviet policy of peaceful coexistence were purged in what became known as the "Revisionist Anti-Party Affair." Militant leaders such as Lê Duẩn and Lê Đức Thọ who favored the Chinese Maoist approach of worldwide revolution took command of the Communist Party and North Vietnam.
The U.S. Joint Chiefs of Staff sent a classified memorandum to U.S. Secretary of Defense McNamara, urging an expansion of U.S. involvement in the war, advocating heavy bombing of North Vietnam, and deployment of troops in South Vietnam for an eventual invasion of the North.
The VC U Minh Battalion overran Năm Căn. It damaged the police station and burned eight military and 20 civilian buildings. Before withdrawing, it used 75mm recoilless rifles to sink a landing craft and two patrol vessels sent to aid the town.
Military Assistance Command, Vietnam – Studies and Observations Group (MACV-SOG) was established to conduct covert unconventional warfare operations in Vietnam.
General Nguyễn Khánh led a successful coup ousting the military junta led by General Dương Văn Minh from the leadership of South Vietnam. It came less than three months after Minh's junta had come to power in a coup d'état which overthrew and killed then President Ngô Đình Diệm. The only casualty of the coup was the execution of Minh's aide, Major Nguyen Van Nhung, and lasted only a few hours. Khánh would allow Minh to resume the office of President nine days later and place himself in the role of prime minister. Minh's colleagues, Generals Tran Van Don, Le Van Kim and Ton That Dinh were placed under house arrest, accused of planning a neutralist takeover of South Vietnam.
Journalist James Reston in The New York Times called for the U.S. to seek a negotiated settlement to the war in South Vietnam. Reston's view echoed that of French President de Gaulle who was advocating that negotiations begin to make South Vietnam a neutral country
February
United States Senate Majority Leader Mike Mansfield told President Johnson that the overthrow of the Minh government was unlikely to result in "significant improvement in the situation" in South Vietnam. Mansfield said the coup was "likely to be only the second in a series as military leaders, released from all civilian restraint, jockey for control of the power which resides in United States aid."
The VC announced a new anti-American terror campaign, offering a bounty of $250 for each American killed. A bomb exploded at the Playboy Bar in Saigon killing five Vietnamese and wounded many other people, including six Americans.
The new leader of South Vietnam, General Khánh, reversed an earlier decision by Minh by giving his approval to the assignment of additional American military and civilian advisers and authorizing U.S.-directed covert operations in North Vietnam under Operation 34A (OPLAN 34A).
The North Vietnamese Vietnam People's Air Force (VPAF) established its first jet fighter unit, the 921st Sao Dao Fighter Regiment. A few weeks later, the first VPAF jet pilots began their training in the Soviet Union.
The VC overran an ARVN battalion headquarters at Hau May killing 12 ARVN.
The VC 504th Battalion and elements of the 261st Battalion successfully attacked the understrength 2nd Battalion, 12th Infantry, at Phu My. The VC killed 13 ARVN, wounded 25, and captured two 81mm mortars, 19 firearms, and six radios. The VC left behind six dead and two weapons. The VC also destroyed the homes of 300 people.
The VC overran an outpost and three hamlets at Ap Ben Cau, 19km south of Tay Ninh City, killing 65 of the 188 Self-Defense Force and militia defenders and capturing 50 weapons. The VC then fortified the hamlets waiting for a government relief force. The ARVN 5th Division responded ineffectively and the VC were able to withdraw. ARVN losses were 27 dead, 66 wounded, and 34 missing. The South Vietnamese claimed, based on captured documents, that the VC had lost 61 dead and 105 wounded. 27 civilians were killed and 29 wounded.
A VC bombing attack on a softball game at Pershing Field killed two Americans and wounded 41, including four women and five children. A second bomb failed to explode.
The VC 71st Battalion overran the district capital of Ba Long in Quang Tri Province, inflicting 38 casualties and capturing four mortars, two machine guns and 86 other weapons.
The VPAF scored its first aerial victory against an American aircraft when a T-28 Trojan, whose pilot had defected to North Vietnam from the Royal Lao Air Force, shot down a C-123 Provider transport.
A VC shot and killed a U.S. MP outside the Kinh Do movie theater and then entered the theater and exploded a bomb killing three Americans with a further 32 wounded, most of them U.S. dependents.
David Nes, the Deputy Chief of Mission of the U.S. Embassy in Saigon, wrote a pessimistic memorandum to Ambassador Lodge and senior officials in Washington. Nes did not see much prospect for the improvement of South Vietnamese performance. He said that escalation of the U.S. military effort might be the only alternative to the neutralization of South Vietnam as proposed by de Gaulle and others.
Khanh issued the Chien Thang (Struggle for Victory) pacification program.
The VC bombed a train travelling from Saigon to Da Nang killing 11.
In the Battle of Long Dinh the ARVN, despite overwhelming numbers and firepower, was not aggressive in its attack and the VC 514th Battalion escaped. The battle resulted in 89 VC killed and two captured and 19 ARVN killed.
March
The 1st and 8th Airborne Battalions commanded by Colonel Cao Văn Viên attempted to encircle the VC 502nd Battalion about 10km north of Tan Chau, near the Cambodian border. Instead, at dawn the VC ambushed the Airborne from entrenched positions using automatic rifles, recoilless rifles, and mortars. Three more infantry battalions and artillery were deployed to support the Airborne. Restrictions on the use of aircraft near the border limited aerial support and the closeness of the combatants sometimes prevented the artillery from firing. The fighting raged until 09:00 when the VC broke contact and fled across the border. ARVN losses were 15 dead and 85 wounded, VC dead were estimated at 130.
Johnson met with the Joint Chiefs of Staff. The Chairman of the Joint Chiefs of Staff General Maxwell Taylor recommended a "progressive and selective attack on targets in North Vietnam." Johnson, however, disagreed, saying that "he did not want to start a war before November" because of the impact an expanded war might have on the Presidential elections that month.
An ARVN 43rd Infantry Regiment operation in the Ara Salour region, a VC base located at the conjunction of Lam Dong, Binh Tuy, and Binh Thuan provinces resulted in 98 VC killed (30 by US helicopter gunships) and 37 captured for the loss of six ARVN and two US killed.
The ARVN captured more than 500 suspected VC in a raid in Kien Phong Province.
An airborne battalion and two ranger companies attempted to envelop two VC battalions near the Cai Cai canal. The operation killed 14 VC and captured 70.