The Gulf of Tonkin incident (Vietnamese: Sự kiện Vịnh Bắc Bộ), also known as the USS Maddox incident, was an international confrontation that led to the United States engaging more directly in the Vietnam War. It involved either one or two separate confrontations between North Vietnam and the United States in the waters of the Gulf of Tonkin. The original American report blamed North Vietnam for both incidents, but the Pentagon Papers, the memoirs of Robert McNamara, and NSA publications from 2005 proved material misrepresentation by the US government to justify a war against Vietnam. On August 2, 1964, the destroyer USS Maddox, while performing a signals intelligence patrol as part of DESOTO operations, was pursued by three North Vietnamese Navy torpedo boats of the 135th Torpedo Squadron. Maddox fired three warning shots and the North Vietnamese boats then attacked with torpedoes and machine gun fire. Maddox expended over 280 3-inch (76.2 mm) and 5-inch (127 mm) shells in a sea battle. One U.S. aircraft was damaged, three North Vietnamese torpedo boats were damaged, and four North Vietnamese sailors were killed, with six more wounded. There were no U.S. casualties. Maddox "was unscathed except for a single bullet hole from a Vietnamese machine gun round."
It was originally claimed by the National Security Agency that a Second Gulf of Tonkin incident occurred on August 4, 1964, as another sea battle, but instead evidence was found of "Tonkin ghosts" (false radar images) and not actual North Vietnamese torpedo boats. In the 2003 documentary The Fog of War, the former United States Secretary of Defense Robert S. McNamara admitted that the August 2 USS Maddox attack happened with no Defense Department response, but the August 4 Gulf of Tonkin attack never happened. In 1995, McNamara met with former Vietnam People's Army General Võ Nguyên Giáp to ask what happened on August 4, 1964, in the second Gulf of Tonkin Incident. "Absolutely nothing", Giáp replied. Giáp claimed that the attack had been imaginary.
The outcome of these two incidents was the passage by Congress of 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". The resolution served as Johnson's legal justification for deploying U.S. conventional forces and the commencement of open warfare against North Vietnam.
In 2005, an internal National Security Agency historical study was declassified; it concluded that Maddox had engaged the North Vietnamese Navy on August 2, but that there were no North Vietnamese naval vessels present during the incident of August 4. The report stated, regarding the first incident on August 2:
As the US sends more troops amid tanker tension with Iran, how far is the Gulf of Oman from the Gulf of Tonkin? "Those who cannot remember the past are condemned to repeat it."at 1500G, Captain Herrick ordered Ogier's gun crews to open fire if the boats approached within ten thousand yards (9,150 m). At about 1505G, Maddox fired three rounds to warn off the communist [North Vietnamese] boats. This initial action was never reported by the Johnson administration, which insisted that the Vietnamese boats fired first.