During the Vietnam War, North Vietnamese intelligence units sometimes succeeded in penetrating Allied communications systems, and they could monitor Allied message traffic from within. But sometimes they did more than that.
On several occasions "the communists were able, by communicating on Allied radio nets, to call in Allied artillery or air strikes on American units."
That is just one passing observation (at p. 392) in an exhaustive history of American signals intelligence (SIGINT) in the Vietnam War that has just been declassified and released by the National Security Agency.
From the first intercepted cable -- a 1945 message from Ho Chi Minh to Joseph Stalin -- to the final evacuation of SIGINT personnel from Saigon, the 500-page NSA volume, called "Spartans in Darkness," retells the history of the Vietnam War from the perspective of signals intelligence.
The most sensational part of the history (which was excerpted and disclosed by the NSA two years ago) is the recounting of the 1964 Gulf of Tonkin Incident, in which a reported North Vietnamese attack on U.S. forces triggered a major escalation of the war. The author demonstrates that not only is it not true, as Secretary of Defense Robert McNamara told Congress, that the evidence of an attack was "unimpeachable," but that to the contrary, a review of the classified signals intelligence proves that "no attack happened that night."
Several other important Vietnam War-era episodes are elucidated by the contribution of SIGINT, including the Tet Offensive, the attempted rescue of U.S. prisoners of war from Son Tay prison, and more.
In light of recent events of course...
A Non-Incident in the Gulf
In what U.S. officials called a serious provocation, Iranian boats harassed and provoked three U.S. Navy ships in the strategic Strait of Hormuz, threatening to explode the American vessels.
Five small boats began charging the U.S. ships, dropping boxes in the water in front of the ships and forcing the U.S. ships to take evasive maneuvers, the Pentagon official said.
There were no injuries but the official said there could have been, because the Iranian boats turned away "literally at the very moment that U.S. forces were preparing to open fire" in self defense.
Unsuprisingly (to some)the Iranians have a different view of the incident... read on.