AC-47 - Nicknamed "Spooky".
Gatling guns, that were individually aimed. Exactly.
Watching them work a ridge line at dusk one evening, it reminded me of an alien space ship from some movie. So many tracers - like beams of light and the deep 'GROWL' of the firing rate - made you glad you were not on the receiving end of those MFer's!
The story was that - a pass over an area the size of a football field would result in a round in EACH SQUARE INCH. Perhaps nothing but a urban legend? But impressive firepower nonetheless.
EDIT:
http://en.wikipedia.org/wiki/Douglas_AC-47_Spooky
Looks like GE Mini Guns - capable of one round in each square yard - my mistake.