Known on US Navy ships as the Close In Weapon System, or CIWS (or Phalanx), in Iraq somebody had the totally awesome idea to mobilize them and use them at ground facilities for. . . . . wait for it. . . . shooting down rockets and mortars! Wicked!! This version is goes by the much cooler name of Counter Rocket, Artillery, and Mortar, or C-RAM. Other countries have 30mm and 40mm versions, but the US CIWS/C-RAM is a 20mm gun.
Rate of fire for the latest system is reportedly 4,500 rounds per minute, and doing the math shows that to equate to 75 rounds per second! That's nasty. I guess it has to be to be able to shoot football sized objects down from several miles away while they're traveling at 3,000+ feet per second. I didn't have this system where I was at, so all incoming rounds just landed wherever, but I would have been glad to have this beast shooting stuff down. Now I wonder how much each round costs so that I can calculate how much a four second burst costs.
ETA: And another one that shows thermal imaging where you can see the actual mortar taking hits and blowing up from the 20mm rounds.
This one's even better!
ETA: All right, so apparently this concept is way more high tech than the CIWS/C-RAM system. The Germans have a 35mm "Revolver" that is way cool at shooting down incoming threats. Hang in there towards the end of the video to see what the rounds do to missiles and such. Awesome!