The Phalanx CIWS (SEE-wiz) is an automated gun-based close-in weapon system to defend military watercraft automatically against incoming threats such as aircraft, missiles, and small boats.

Consisting of a radar-guided 20 mm (0.8 in) Vulcan cannon mounted on a swiveling base, the Phalanx has been used by the United States Navy and the naval forces of 15 other countries.

The U.S. Navy deploys it on every class of surface combat ship, except the Zumwalt-class destroyer and San Antonio-class amphibious transport dock.

The first prototype system was offered to the U.S. Navy for evaluation on the destroyer leader USS King in 1973 and it was determined that further work was required to improve performance and reliability.

This proven system was combined with a purpose-made mounting, capable of fast elevation and traverse speeds, to track incoming targets.

Owing to this self-contained nature, Phalanx is ideal for support ships, which lack integrated targeting systems and generally have limited sensors.

[citation needed] Because of their distinctive barrel-shaped radome and their automated operation, Phalanx CIWS units are sometimes nicknamed "R2-D2" after the droid from the Star Wars films.

The Block 1 (1988) upgrade improved radar, ammunition, computing power, rate of fire, and an increase in maximum engagement elevation to +70 degrees.

[11] This addition was developed to provide ship defense against small vessel threats and other "floaters" in littoral waters and to improve the weapon's performance against slower low-flying aircraft.

In addition to the FLIR sensor, the Block 1B incorporates an automatic acquisition video tracker, optimized gun barrels (OGB), and Enhanced Lethality Cartridges (ELC) for additional capabilities against asymmetric threats such as small maneuvering surface craft, slow-flying fixed and rotary-winged aircraft, and unmanned aerial vehicles.

[13] In April 2017, Raytheon tested a new electric gun for the Phalanx allowing the system to fire at varying rates to conserve ammunition.

For full operation, including some nonessential functions, it also has inputs for ship's true compass heading and 115 V AC for the WinPASS subsystem.

WinPASS (Windows-based Parameter Analysis and Storage Subsystem) is a secondary computer built into the local control station that allows technicians to perform various tests on system hardware and software for maintenance and troubleshooting purposes.

The search subsystem provides bearing, range, velocity, heading, and altitude information of potential targets to the CIWS computer.

[citation needed] On 10 February 1983, USS Antrim was conducting a live-fire exercise off the East Coast of the United States using the Phalanx against a target drone.

On 13 October 1989, USS El Paso was conducting a live-fire exercise off the East Coast of the United States using the Phalanx against a target drone.

[17] On 17 May 1987, during the Iran–Iraq War, which the US was observing as a non-combatant, an Iraqi Dassault Mirage F1 fighter[18] fired two Exocet missiles at what was deemed to be a suitable target, but was the American frigate USS Stark.

[20] On May 5, 1994, the port side Phalanx on board the USS Lake Erie accidentally fired two depleted uranium rounds while the ship was at its berth at Pearl Harbor, Hawaii.

A Judge Advocate General investigation concluded that required CIWS pre and post-firing inspections had not been properly conducted and the rounds had gone undetected in the ammunition drive.

[21][22][23] On 4 June 1996, a Phalanx operated by the JMSDF accidentally shot down a US A-6 Intruder from the aircraft carrier USS Independence that was towing a radar target during gunnery exercises about 1,500 mi (2,400 km) west of the main Hawaiian island of Oahu.

For all intents and purposes a terrestrial version of the Navy's CIWS, the Centurion was rapidly developed,[31] with a proof-of-concept test in November that same year.

However, the swift and effective development and performance of Israel's indigenous Iron dome system has ruled out any purchase or deployment of Centurion.

[36] Like the naval (1B) version, Centurion uses Ku-band radar and FLIR[37][38] to detect and track incoming projectiles, and is also capable of engaging surface targets, with the system able to reach a minus-25-degree elevation.