The outcome of the incidents was the passage by Congress of the Southeast Asia Resolution (better known as the Gulf of Tonkin Resolution), which granted President Lyndon B. Johnson the authority to assist any Southeast Asian country whose government was considered to be jeopardized by "communist aggression," including the commitment of U.S. forces without a declaration of war. The resolution served as Johnson's legal justification for escalating American involvement in the Republic of Vietnam (South Vietnam).
In 2005, an official NSA declassified report revealed that the Maddox had engaged the North Vietnamese, but that there may not have been any North Vietnamese vessels present during the engagement of 4 August. The report stated
The Gulf of Tonkin Incident occurred during the first year of the Johnson administration. While Kennedy had originally supported the policy of sending military advisers to Vietnam, he had begun to alter his thinking due to what he perceived to be the ineptitude of the Saigon government and its inability and unwillingness to make needed reforms (which led to an American-supported coup which resulted in the death of Diem). Shortly before his assassination in November 1963, Kennedy had begun limited recall of American forces. Johnson's views were likewise complex, but he had supported military escalation in Vietnam as a means to challenge what he perceived as the expansionist policies of the Soviet Union. The Cold War policy of containment was to be applied to prevent the fall of Southeast Asia to communist governments under the precepts of the domino theory. After Kennedy's assassination, Johnson ordered in more American forces to support the Saigon government, beginning a protracted United States presence in Southeast Asia.
According to the U.S. Naval Institute, a highly classified program of covert actions against North Vietnam known as Operation Plan 34-Alpha, had begun under the Central Intelligence Agency (CIA) in 1961. In 1964 the program was transferred to the Defense Department and conducted by the Military Assistance Command, Vietnam Studies and Observations Group (SOG).
For the maritime portion of the covert operation, Tjeld-class fast patrol boats had been purchased quietly from Norway and sent to South Vietnam. Although the crews of the boats were South Vietnamese naval personnel, approval of the plan came directly from Admiral U.S. Grant Sharp, Jr., CINCPAC in Honolulu. After the coastal attacks began, Hanoi lodged a complaint with the International Control Commission (ICC), which had been established in 1954 to oversee the terms of the Geneva Accords, but the U.S. denied any involvement. Four years later, Secretary of Defense Robert S. McNamara admitted to Congress that the U.S. ships had in fact been cooperating in the South Vietnamese attacks against North Vietnam. Maddox, although ostensibly aware of the operations, was not directly involved.
What was (and is) generally not considered by U.S. politicians at the time (and by later historians) were the other actions taken under Operations Plan 34-Alpha just prior to the incidents. The night before the launching of the actions against North Vietnamese facilities on Hon Me and Hon Ngu islands, SOG had launched a covert long-term agent team into North Vietnam, which was promptly captured. That night (for the second evening in a row) two flights of CIA-sponsored Laotian fighter-bombers (piloted by Thai mercenaries) attacked border outposts well within southwestern North Vietnam. The Hanoi government (unlike the American government, which had to give permission at the highest levels for the conduct of these missions) probably assumed that they were all a coordinated effort to escalate military actions against North Vietnam.
This account, however, has come into sharp dispute with an official 2005 NSA declassified report which stated on page 17:
Even before this was revealed, however, some had held that the actions of the Maddox (i.e., merely the presence of the vessel in particular places and times) were provocative to the North Vietnamese because they coincided with the covert South Vietnamese raids. Since the Desoto patrols were conducted in order to gather just the sort of electronic emissions that the SOG 34-Alpha raids would provoke, it was a reasonable assumption that the two were "piggybacked." The destroyer's presence also may have been mistaken by the North Vietnamese as a sign that it was also involved directly in the raids.
Others, such as Admiral Sharp, maintained that U.S. actions did not provoke the 2 August action. He claimed that North Vietnamese radar had tracked Maddox along the coast, and was thus aware that the destroyer had not actually attacked North Vietnam and that Hanoi (or the local commander) had ordered its craft to engage Maddox anyway. Sharp also noted that orders given to Maddox to stay eight miles (13 km) off the North Vietnamese coast put the ship in international waters, as North Vietnam claimed only a five-mile (8 km) nautical limit as its territory (or off of its off-shore islands). In addition, many nations had previously carried out similar missions all over the world, and the USS John R. Craig had earlier conducted an intelligence-gathering mission in similar circumstances without incident.
At 0127 Washington time, Herrick sent a cable in which he admitted that the attack may never have happened and that there may actually have been no Vietnamese craft in the area: "Review of action makes many reported contacts and torpedoes fired appear doubtful. Freak weather effects on radar and overeager sonarmen may have accounted for many reports. No actual visual sightings by Maddox. Suggest complete evaluation before any further action taken
One hour later, Herrick sent another cable, stating, "Entire action leaves many doubts except for apparent ambush at beginning. Suggest thorough reconnaissance in daylight by aircraft." In response to requests for confirmation, at around 1600 Washington time, Herrick cabled, "Details of action present a confusing picture although certain that the original ambush was bona fide."
At 1800 Washington time (0500 in the Gulf of Tonkin), Herrick cabled yet again, this time stating, "the first boat to close the Maddox probably fired a torpedo at the Maddox which was heard but not seen. All subsequent Maddox torpedo reports are doubtful in that it is suspected that sonarman was hearing ship's own propeller beat" [sic].
As a result of his testimony, on 7 August, Congress passed a joint resolution (H.J. RES 1145), titled the Southeast Asia Resolution, which granted President Johnson the authority to conduct military operations in Southeast Asia without the benefit of a declaration of war. The Resolution gave President Johnson approval "to take all necessary steps, including the use of armed force, to assist any member or protocol state of the Southeast Asia Collective Defense Treaty requesting assistance in defense of its freedom."
In 1981, Captain Herrick and journalist Robert Scheer re-examined Herrick's ship's log and determined that the first torpedo report from 4 August, which Herrick had maintained had occurred—the "apparent ambush"—was in fact unfounded.
Although information obtained well after the fact supported Captain Herrick's statements about the inaccuracy of the later torpedo reports as well as the 1981 Herrick/Scheer conclusion about the inaccuracy of the first, indicating that there was no North Vietnamese attack that night, at the time U.S. authorities and all of the Maddox crew stated that they were convinced that an attack had taken place. As a result, planes from the carriers Ticonderoga and Constellation were sent to hit North Vietnamese torpedo boat bases and fuel facilities during Operation Pierce Arrow.
Squadron commander James Stockdale was one of the U.S. pilots flying overhead during the second alleged attack. Stockdale wrote in his 1984 book Love and War: "[I] had the best seat in the house to watch that event, and our destroyers were just shooting at phantom targets—there were no PT boats there… There was nothing there but black water and American fire power." Stockdale said his superiors ordered him to keep quiet about this. After he was captured, this knowledge became a heavy burden. He later said he was concerned that his captors would eventually force him to reveal what he knew about the second incident.
In 1995, retired Vietnamese Defense Minister Vo Nguyen Giap, meeting with former Secretary of Defense McNamara, categorically denied that Vietnamese gunboats had attacked American destroyers on 4 August, while admitting to the attack on 2 August. A taped conversation of a meeting several weeks after passage of the Gulf of Tonkin Resolution was released in 2001, revealing that McNamara expressed doubts to President Johnson that the attack had even occurred.
In the Fall of 1999, retired senior CIA engineering executive S. Eugene Poteat wrote that he was asked in early August 1964 to determine if the radar operator's report showed a real torpedo boat attack or an imagined one. He asked for further details on time, weather and surface conditions. No further details were forthcoming. In the end he concluded that there were no torpedo boats on the night in question, and that the White House was interested only in confirmation of an attack, not that there was no such attack.
Hanyok's conclusions were initially published within the NSA in the Winter 2000/Spring 2001 Edition of Cryptologic Quarterly, about five years before they were revealed in the Times article. According to intelligence officials, the view of government historians that the report should become public was rebuffed by policymakers concerned that comparisons might be made to intelligence used to justify the Iraq War that commenced in 2003. Reviewing the NSA's archives, Mr. Hanyok concluded that the NSA had initially misinterpreted North Vietnamese intercepts, believing there was an attack on 4 August. Midlevel NSA officials almost immediately discovered the error, he concluded, but covered it up by altering documents, so as to make it appear the second attack had happened.
On 30 November 2005, the NSA released the first installment of previously classified information regarding the Gulf of Tonkin incident, including Mr. Hanyok's article, "Skunks, Bogies, Silent Hounds, and the Flying Fish: The Gulf of Tonkin Mystery, 2–4 August 1964" Cryptologic Quarterly, Winter 2000/Spring 2001 Edition, Vol. 19, No. 4 / Vol. 20, No. 1. The Hanyok article stated that intelligence information was presented to the Johnson administration "in such a manner as to preclude responsible decisionmakers in the Johnson administration from having the complete and objective narrative of events." Instead, "only information that supported the claim that the communists had attacked the two destroyers was given to Johnson administration officials."
With regards to why this happened, Hanyok wrote:
The full NSA report was released in January 2008 by the National Security Agency and published by the Federation of American Scientists, retelling the Vietnam War from the perspective of "signals intelligence".