In 1964 North Vietnamese forces supposedly attacked a US destroyer in the Gulf of Tonkin. President Johnson used this incident to obtain approval for the Vietnam War from Congress.

But on Tuesday the National Security Agency declassified documents revealing -- to almost no one's surprise -- that the Gulf of Tonkin incident never happened.

Also on Tuesday, by an odd coincidence, the US military released video of an incident in a different Gulf... the Persian one.

The video shows Iranian speedboats approaching US warships. Then (separately) a heavily accented voice says over the radio, in English, “I am coming to you. … You will explode after … minutes.” (The video is on youtube)

The incident inflamed tensions between the two countries, but now it's looking like there are problems interpreting exactly what was happening in the Persian Gulf video.

As the US military admits, the audio and video weren't recorded together. And skeptics have been wondering why, if the audio did come from the Iranian speedboats (as the military implied) there was no sound of wind or water in the background.

It's starting to look more like the threatening audio was from some random guy with a radio on land.

Iran, for its part, is saying that the incident was just "a routine contact which happens all the time in the crowded waters of the Gulf." Not that I find anything the Iranian government says to be very credible. It's hard to know what to believe.