Case Closed: The Gulf of Tonkin Incident

Wednesday, August 13th, 2014

The Gulf of Tonkin Incident involved a second incident in the gulf, two days after a minor clash:

When the contacts appeared to turn away at 6,000 yards, Maddox’s crew interpreted the move as a maneuver to mark a torpedo launch. The ship’s sonar operator reported a noise spike — not a torpedo — which the Combat Information Center (CIC) team mistook for report of an incoming torpedo.

Both U.S. ships opened fire on the radar contacts, but reported problems maintaining a lock on the tracking and fire control solution. The first reports of the encounter from the destroyers reached the White House at 1000 EDT. Two hours later, Captain Herrick reported the sinking of two enemy patrol boats.

With this information, back in Washington President Johnson and his advisers considered their options. By 1400 hours EDT, the president had approved retaliatory strikes against North Vietnamese naval bases for the next morning, August 5, at 0600 local time, which was 1900 EDT on August 4 in Washington. In the meantime, aboard Turner Joy, Captain Herrick ordered an immediate review of the night’s actions.

His assessment of the evidence now raised doubts in his mind about what really had happened. He reported those doubts in his after action report transmitted shortly after midnight his time on August 5, which was 1300 hours August 4 in Washington.

Herrick requested aerial reconnaissance for the next morning to search for the wreckage of the torpedo boats he thought he had sunk. Both of these messages reached Washington shortly after 1400 hours EDT. Neither Herrick’s doubts nor his reconnaissance request was well received, however. The Pentagon had already released details of the “attack,” and administration officials had already promised strong action. Then, everyone’s doubts were swept away when a SIGINT intercept from one of the North Vietnamese torpedo boats reported the claim that it had shot down two American planes in the battle area.

McNamara and the JCS believed that this intercept decisively provided the “smoking gun” of the second attack, and so the president reported to the American people and Congress.

A subsequent review of the SIGINT reports revealed that this later intercept — McNamara’s “smoking gun” — was in fact a follow-on, more in-depth report of the August 2 action. Moreover, the subsequent review of the evidence exposed the translation and analysis errors that resulted in the reporting of the salvage operation as preparations for a second attack. In fact, the North Vietnamese were trying to avoid contact with U.S. forces on August 4, and they saw the departure of the Desoto patrol ships as a sign that they could proceed to recover their torpedo boats and tow them back to base.

They never intended to attack U.S. forces, and were not even within 100 nautical miles of the U.S. destroyers’ position at the time of the purported “second engagement.”

NSA officials handed the key August SIGINT reports over to the JCS investigating team that examined the incident in September 1964. Those same reports were shown to the select congressional and senate committees that also investigated the incident. The entirety of the original intercepts, however, were not examined and reanalyzed until after the war.

The 122 additional relevant SIGINT products confirmed that the Phu Bai station had misinterpreted or mistranslated many of the early August 3 SIGINT intercepts. With that false foundation in their minds, the on-scene naval analysts saw the evidence around them as confirmation of the attack they had been warned about.

Those early mistakes led U.S. destroyers to open fire on spurious radar contacts, misinterpret their own propeller noises as incoming torpedoes, and ultimately report an attack that never occurred.

Despite the on-scene commanders’ efforts to correct their errors in the initial after-action reports, administration officials focused instead on the first SIGINT reports to the exclusion of all other evidence. Based on this, they launched the political process that led to the war’s escalation.

The Gulf of Tonkin Incident and many more recent experiences only reinforce the need for intelligence analysts and decision makers to avoid relying exclusively on any single intelligence source — even SIGINT — particularly if other intelligence sources are available and the resulting decisions might cost lives. Signals Intelligence is a valuable source but it is not perfect. It can be deceived and it is all too often incomplete. Like all intelligence, it must be analyzed and reported in context. People are human and make mistakes, particularly in the pressure of a crisis or physical threat to those they support. Perhaps that is the most enduring lesson from America’s use of SIGINT in the Vietnam War in general and the Gulf of Tonkin Incident in particular.

(Hat tip to our Slovenian guest.)


  1. Toddy Cat says:

    Was that little detail about the North trying to conquer the South for twenty years using everything from terrorism to heavy armor propeller noise as well?

    But McNamara was an idiot, no argument there.

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