A needle gun is a pneumatic tool used by the US Navy for the preservation of a ship. They are used extensively on the hull of the ship, bulkheads, decks, hatches, and scuttles to remove corrosion, paint, barnacles, and whatever else the boatswain's mates deem fit.
Truly a simple tool, the gun uses a trigger to pump low pressure air into the cylinder that holds one large piston. This piston, in turn, sporadically and randomly moves approximately twenty needles which act as miniature paint chippers on crack.
It makes the life of an average deck seaman like myself much easier because without the aforementioned tool, people like myself would spend countless hours with chipping hammers beating away at the ship.