The book "Designated Targets" - a fascinating time travel/alternative history yarn - posited a ship defense system called "Metal Storm" - a system that would fill the air with enough shrapnel to stop any incoming attack.

Well, it seems that the author wasn't talking out of his hat - have a look here. The description certainly sounds like the one from the book:

The U.S. Army plans to test next month a SUPER GUN from a company appropriately called Metal Storm that can shoot 240,000 bullets per minute. The gun has no moving parts. Among its many tricks, the gun can actually shoot down enemy mortar fire. I want one.