Yet both were major turning points of the Vietnam conflict. The Gulf of Tonkin led to open US involvement in the fighting. Tet, though a tactical military defeat for the North, was a surprise for a US public that had been led to believe victory might be imminent. It may have contributed to declining support for the American intervention.
The Gulf of Tonkin incident occurred in early August 1964. On Aug. 2, North Vietnamese patrol boats attacked a US destroyer, the USS Maddox, in the Gulf of Tonkin, an arm of the South China Sea off Vietnam's northeastern coast. Mr. Johnson warned the North that another such attack would bring "grave consequences." On Aug. 4, Johnson announced that another attack had occurred and asked Congress to vote him powers to respond. On Aug. 7, Congress gave him those powers in the Gulf of Tonkin resolution, which became the legal foundation for increased US involvement.
Even at the time, some doubted that the second attack had occurred. Yet the Johnson administration produced what seemed a key piece of evidence – a North Vietnamese Navy after-action report, intercepted by the NSA, which appeared to discuss the battle.
In fact, the intercept had been mistranslated, according to the just-released report. The Vietnamese word for "military operations" can also mean "long movement," and the intercept in reality referred to the towing of two North Vietnamese patrol boats some distance for repairs.
Furthermore, US intelligence intercepted no communications or radar emissions associated with the assumed attack. Mr. Hanyok, the NSA historian, cites Sherlock Holmes, who famously once solved a case because a dog did not bark, proving something did not occur.
"As Holmes would come to conclude that no crime was committed, so we must conclude that, since [signals intelligence] never intercepted anything associated with an attack, none ever occurred," Hanyok writes.