Phalanx CIWS

"The Phalanx CIWS is a close-in weapon system for defence against anti-ship missiles. It was designed and manufactured by the General Dynamics Corporation, Pomona Division[4] (now a part of Raytheon). Consisting of a radar-guided 20 mm (0.79 in) Gatling gun mounted on a swiveling base, the Phalanx has been used by multiple Navies around the world, notably the United States Navy on every class of surface combat ship, with the exception of the San Antonia-class LPD."

-Wikipedia

Update (added 4 more barrels and resized the dome)