I recently read The Secret Sentry by Matthew Aid, which is a history of the National Security Agency. (I snapped it up for $2.99 when Amazon put the Kindle version on sale.)
Many of the book's revelations were news to me, such as the fact that American forces intervened directly in the civil war in El Salvador (as opposed to sending supplies and advisers, which everyone knew about at the time.)
The El Salvador revelation is included in Chapter 10, Aid describes how reconnaissance aircraft were used to monitor the FMLN, the leftist rebels. He writes, "If he location of FMLN radio transmitters were triangulated, U.S. Air Force AC-130 gunships were called in from Panama to destroy the guerrilla bases, all of which was done in complete secrecy. It was a very serious and very secret war that was being fought in El Salvador." (Aid's notes on the chapter cites a "60 Minutes" TV program from May 21, 1995, as his source for the gunship attacks.)
I was paying close attention to the El Salvador news at the time, and I don't remember anyone reporting this. As usual, the information that U.S. gunships were actively involved was carefully hidden from the American's government's main enemy, the American people.