How did American involvement in Vietnam change during the Kennedy & Johnson administrations?

When President Kennedy took office in 1961, he continued to support South Vietnam, believing the country was vital in the battle against communism. From 1961 to late 1963, the number of U. S. military personnel in South Vietnam jumped from about 2,000 to around 15,000. Yet they failed to shore up the floundering Diem regime. For example, the South Vietnamese created special fortified villages known as strategic hamlets. They then moved villagers to these hamlets, despite the peasants' resentment at being uprooted from their villages. The program proved to be extremely unpopular.

On August 2, 1964, Johnson announced that North Vietnamese torpedo boats had fired on two U. S. destroyers in the Gulf of Tonkin. Two days later, he reported another attack. Insisting that these were unprovoked, he ordered American aircraft to attack North Vietnamese ships and naval facilities.