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 President 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
2 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.
10 January
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.
14 January
Theodore Sorensen, one of former President John F. Kennedy's most trusted aides, wrote President 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 is appointed deputy commander of MACV.
20 January
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).