The Phalanx Close-In Weapons System (CIWS) was developed as the last line of automated weapons defense (terminal defense or point defense) against anti-ship missiles (AShMs), including high-g and maneuvering sea-skimmers. The basis of the system is the M61 Vulcan Gatling gun autocannon.
Consisting of a radar-guided 20 mm (0.79 in) Gatling gun mounted on a swiveling base, the Phalanx has been used by Navies around the world.
The CIWS is designed to be the last line of defense against anti-ship missiles. Due to its design criteria, its effective range is very short relative to the range of modern ASMs, from 1 to 5 nautical miles (9 km). The gun mount moves at a very high speed and with great precision. The system takes minimal inputs from the ship, making it capable of functioning despite potential damage to the ship. (en.wikipedia.org/wiki/Phalanx_CIWS) Credit: PO3 Samuel Souvannason, PO1 Henry Dunphy, SN David Flewellyn, SN Patrick Dionne. Additional editing: AiirSource