The Phalanx ship-based anti-missile system is well-known: it combines a 20mm gatling gun that can fire 3,000 or 4,500 rounds per minute with a Ku-band radar resulting in autonomous targeting and engagement.
When a new problem emerged - rocket, artillery and mortar attacks in urban settings like Baghdad and the need to protect high-value sites and population centers, Raytheon and the US Navy adapted Phalanx to land-based applications. The name of the new solution is Centurion (pdf).
The Phalanx/Centurion has a very distinctive, chainsaw-starting-like sound. Click here to watch a video and hear the sound.
When I spoke with Raytheon employees at AUSA, they were especially excited about Centurion's role in keeping troops safe, citing over 100 shootdowns in Iraq.