On 2 August 1964, USS Maddox, on an intelligence mission along North Vietnam's coast, allegedly fired upon and damaged several torpedo boats that had been stalking it in the Gulf of Tonkin. A second attack was reported two days later on USS Turner Joy and Maddox in the same area. The circumstances of the attacks were murky.–219 Lyndon Johnson commented to Undersecretary of State George Ball that "those sailors out there may have been shooting at flying fish." An undated NSA publication declassified in 2005 revealed that there was no attack on 4 August.

The second "attack" led to retaliatory airstrikes, and prompted Congress to approve the Gulf of Tonkin Resolution on 7 August 1964. The resolution granted the president power "to take all necessary measures to repel any armed attack against the forces of the United States and to prevent further aggression" and Johnson would rely on this as giving him authority to expand the war. In the same month, Johnson pledged that he was not "committing American boys to fighting a war that I think ought to be fought by the boys of Asia to help protect their own land".

The National Security Council recommended a three-stage escalation of the bombing of North Vietnam. Following an attack on a U.S. Army base in Pleiku on 7 February 1965, a series of airstrikes was initiated, Operation Flaming Dart. Operation Rolling Thunder and Operation Arc Light expanded aerial bombardment and ground support operations. The bombing campaign, which ultimately lasted three years, was intended to force North Vietnam to cease its support for the Viet Cong by threatening to destroy North Vietnamese air defenses and industrial infrastructure. It was additionally aimed at bolstering the morale of the South Vietnamese.