On August 1, 1964, North Vietnamese torpedo boats attacked an American destroyer as it conducted espionage in the Gulf of Tonkin off North Vietnam. Two nights later, two vessels reported another attack. Though no firm evidence of an attack by North Vietnam surfaced, President Lyndon Johnson used the reports to justify a retaliation against the North Vietnamese for repeated acts of violence. Johnson requested and received from Congress blanket authorization to respond as he chose to any future aggression by the North Vietnamese. The Gulf of Tonkin Resolution became the legislative foundation for the Vietnam War, as the United States never actually declared war upon North Vietnam.