Answer: the United States was unaware of any South Vietnamese attacks on North Vietnam.
Step-by-step explanation: The Gulf of Tonkin Resolution was a resolution made by the United States Congress in 1964. The Resolution was taken right after the event that became to be known as The Gulf of Tonkin Incident.
Back then, Vietnam was divided into North Vietnam, communist, and South Vietnam, non-communist and supported by the USA. On August 2, 1964, a US destroyer called USS Maddox reported being attacked by North Vietnamese torpedo boats. Two days later, both USS Maddox and Turner Joy destroyers reported being under attack again by North Vietnamese torpedo boats. However, this second attack has never been confirmed. In fact, the government in Hanoi insisted that the second attack was not louched, but it admitted the first one.
Two days after the supposed attack on August 4, the US Defense Secretary McNamara testified before the US Congress stating that the destroyer Maddox was carrying out a routine mission. He did not mention that, in fact, the destroyer was part of the Operation Plan 34A, a program of clandestine attacks on North Vietnamese installations. Those operations were carried by South Vietnamese soldiers, trained by and under the control of US military commands.
After a short discussion, the Congress voted a jointed resolution authorizing the President of the United States to take all the necessary measures. In other words, the President would now have the power to retaliate even though he hadn't declared war. Because of this resolution, the US started a rapid escalation towards war.