- June 20 – General William Westmoreland assumes command of all U.S. forces in Vietnam.
- July 6 – Some 900 Viet Cong attack Nam Dong, a U.S. Special Forces camp defended by 12 Green Berets, about 300 South Vietnamese and a few other allied fighters, who force the enemy to retreat. Captain Roger Donlon receives the first Medal of Honor presented in the Vietnam War.
- Aug 2 – U.S. destroyer Maddox, in the Gulf of Tonkin to gather intelligence from electronic transmissions, is attacked by three North Vietnamese P-4 class motor torpedo boats and suffers minor damage.
- Aug 3 – The Maddox returns to the Gulf, along with another destroyer, the Turner Joy.
- Aug 4 – The destroyers pick up radar and sonar signals that their crews interpret as North Vietnames vessels moving in for an attack. The U.S. ships begin firing. (Later investigations indicate that the Maddox and Turner Joy were not attacked.)
- Aug 5 – President Lyndon B. Johnson orders airstrikes agains North Vietnam.
- Aug 7 – Congress approves the Gulf of Tonkin Resolution, giving Johnson “all necessary measures to repel any attack against the enemy forces of the United States to prevent further aggression.”
President Lyndon B. Johnson, Aug. 5, 1964, in a speech at Syracuse University in New York, after a North Vietnames attack on the U.S. Navy in the Gulf of Tonkin:
The world must never forget – that aggression unchallenged is aggression unleashed. We of the United States have not forgotten. This is why we have answered this aggression with action.