If they did, I recreated what it would have sounded like, in French, using International Morse, and again in American Morse (in English). I posted it in a link in the /r/amateurradio subreddit here (warning, it is a bit loud)

Not sure if this counts as a "source" per se, especially, but it at least recreates a primary source (though I can't recreate the "fist" of the original operator of course).

If it happened in 1997, it's outside the 20 year scope of this subreddit

Isn't the Coast Guard part of the Navy?