As a former field artilleryman, I can comment on "friendly fire" from a different perspective. It wasn't invented by a PR flac, rather its a technical (well, not very) term that's been around at least since WWII. It refers to artillery rounds (shells, if you prefer) fired ("fire") by our side ("friendly")that hit something other than the intended target. This can be because of mislocation of the target or of the guns, changing weather conditions, mathmatical error, or because either the good guys weren't where they were supposed to be or the artillery didn't know where they were.