A “mandatory declassification” request has forced the National Security Agency to declassify information regarding the Vietnam War in the form of a report. The agency was responsible for much of the United States’ codebreaking and eavesdropping work during the war.

The 500-page report reveals that during the war, North Vietnamese intelligence units were occasionally successful in penetrating US communications systems. This allowed them to monitor American message traffic and “call in Allied artillery or air strikes on American units” by communicating on Allied radio nets. Steven Aftergood, director of the Federation of American Scientists (FAS) project on government secrecy remarked, “That’s something I have never heard before.”

However, the “most historically significant feature,” according to Aftergood, is the declassified retelling of the Gulf of Tonkin incident. The official claim is that the North Vietnamese attacked American destroyers in 1964. This led to an escalation of American forces in Vietnam. “What this study demonstrated is that the available intelligence shows that there was no attack. It’s a dramatic reversal of the historical record,” Aftergood says. “There were previous indications of this but this is the first time we have seen the complete study.”

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