Declassified study puts Vietnam events in new light
US signals intelligence during the war came up short in major turning points, according to an NSA history.
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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.Skip to next paragraph
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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.
The Tet offensive erupted on Jan. 30, 1968, in which North Vietnamese forces and their Viet Cong allies attacked major cities in South Vietnam. The attack demoralized the US public and many of its political and military leaders. Just days earlier, US commander in chief Gen. William Westmoreland had assured them the enemy was largely beaten.
In terms of signals intelligence, Tet may have been an example of what intelligence analysts call the "Ultra problem," after the famous Ultra code breakers of World War II: the tendency of military and political leaders to look at electronic intercepts as gold, magic, and the keys to victory rolled into one.
At that period in the war, the overwhelming bulk of radio intercepts came from North Vietnamese army units operating in the demilitarized zone between the two countries, and the Central Highland region. Thus, that was where General Westmoreland focused his attention, and where he believed the next major attack would come.
Yet communist units in the South had learned radio discipline to hide their movements. US intelligence did pick up communications talking of an attack on Saigon and other cities, and even heard reference to an "N-day" of the offensive's launch.
But no one date was named as N-day. "The exact date remained unknown, and the other indicators were never fully realized in the NSA reporting," says the agency history.
Thus a major turning point in the war was not predicted in advance, at least by eavesdropping and other electronic means.
With both the Gulf of Tonkin and Tet "it is easy to see how ... crimped analytic capability, especially in cryptanalysis, and the lack of sufficient qualified linguists affected NSA reporting," concludes Hanyok.
The NSA history of signals intelligence during the Vietnam conflict, "Spartans in Darkness: American SIGINT and the Indochina War, 1945-1975" was written in 2002. It is posted on the website of the Federation of American Scientists Project on Government Secrecy.