two separate occasions. While the first incident barely damaged the USS Maddox and resulted in 10 Vietnamese casualties (4 killed and 6 wounded), the second incident was contentious, and was proven to not have happened in the 2000s. However, at the time, U.S. President Lyndon B. Johnson used both incidents as justification to take any necessary retaliatory measures; the U.S. Congress promptly passed the Gulf of Tonkin Resolution, which authorized the deployment of American forces in Vietnam. The Gulf of Tonkin incident started American involvement in the Second Indochina War, known in the Western world as the "Vietnam War". For 11 years, the U.S, South Vietnam, and their allies fought North Vietnam, the Viet Cong, and their allies. Though the U.S. and South Vietnam used air superiority, close air support, and Central Intelligence Agency-led intelligence operations to their advantage, North Vietnam and the Viet Cong made use of guerrilla warfare, though their tactics gradually became more conventional as the war progressed. The Vietnam War was a massive undertaking for all involved: North Vietnam and the Viet Cong had around 690,000 soldiers by 1966, South Vietnam had a strength of 1.5 million soldiers by 1972, and the U.S. deployed a total of 2.7 million soldiers over the course of American involvement, peaking at 543,000 in April 1969. The U.S. spent roughly $140 billion ($950 billion in 2011) in direct expenses to South Vietnam to build infrastructure, train an army and police force, and modernize the country. Casualties and destruction caused by the war were immense, with the conflict killing between 1.3 million and 3.4 million people, a combined total of combatants and non-combatants from both sides. American society was greatly polarized by the war, which coincided with the height of the counterculture phenomenon and civil rights movement; opposition to American involvement in the Vietnam War was related to these movements, but was a major and significant movement in its own right. American sympathies toward and perspectives on Vietnam depended on political stance, and the U.S. government itself experienced divisions between pro-war and anti-war politicians. To the United States, the Vietnam War was a Cold War conflict of political ideologies. Though the U.S. outwardly intervened in the interests of freedom, determination, and sovereignty, this was only when communism was not a major factor. However, North Vietnam was a communist country with relations to communist China and the Soviet Union, and was already