20mm Phalanx

### Users

Australia, Bahrain, Canada, Chile, Ecuador, Egypt, Greece, India, Israel, Japan, Mexico, New Zealand, Pakistan, Poland, Portugal, Saudi Arabia, South Korea, Thailand, Turkey, Taiwan, UK, USA (current), Afghanistan, Malaysia (former)

### Designer

General Dynamics

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. It was designed and manufactured by the General Dynamics Corporation, Pomona Division, later a part of Raytheon. 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 US Navy deploys it on every class of surface combat ship, except the *Zumwalt*-class destroyer and *San Antonio*-class amphibious transport dock. Other users include the British Royal Navy, the Royal Australian Navy, the Royal New Zealand Navy, the Royal Canadian Navy, and the U.S. Coast Guard.

A land variant, the LPWS (Land Phalanx Weapon System), part of the C-RAM system, was developed. It was deployed to counter rocket, artillery and mortar attacks during the 2021 US withdrawal from Afghanistan. The U.S. Navy also fields the SeaRAM system, which pairs the RIM-116 Rolling Airframe Missile with sensors based on the Phalanx.

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.

### History

The Phalanx Close-In Weapons System (CIWS) was developed as the last line of automated weapons defense (terminal defense or point defense) against all incoming threats, including antiship missiles (AShMs or ASMs), aircraft including high-g and maneuvering sea-skimmers, and small boats.

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. Subsequently, the Phalanx Operational Suitability Model successfully completed its Operational Test and Evaluation (OT&E) on board the destroyer USS *Bigelow* in 1977. The model exceeded operational maintenance, reliability, and availability specifications. Another evaluation successfully followed, and the weapon system was approved for production in 1978. Phalanx production started with orders for 23 USN and 14 foreign military systems. The first ship fully fitted out was the aircraft carrier USS *Coral Sea* in 1980. The Navy began placing CIWS systems on non-combatant vessels in 1984.

### Design

The basis of the system is the 20 mm M61 Vulcan Gatling gun autocannon, used by the United States military on various tactical aircraft since 1959, linked to a Ku band fire control radar system for acquiring and tracking targets. This proven system was combined with a purpose-made mounting, capable of fast elevation and traverse speeds, to track incoming targets. An entirely self-contained unit, the mounting houses the gun, an automated fire-control system and all other major components, enabling it to automatically search for, detect, track, engage, and confirm kills using its computer-controlled radar system. Owing to this self-contained nature, Phalanx is ideal for support ships, which lack integrated targeting systems and generally have limited sensors. The entire unit has a mass between 12,400 to 13,500 lb (5,600 to 6,100 kg).

#### Upgrades

Due to the evolution of threats and computer technology, the Phalanx system has been developed through several configurations. The basic (original) style is the Block 0, equipped with first-generation, solid-state electronics and with marginal capability against surface targets. The Block 1 (1988) upgrade offered various improvements in radar, ammunition, computing power, rate of fire, and an increase in maximum engagement elevation to +70 degrees. These improvements were intended to increase the system's capability against emerging Russian supersonic anti-ship missiles. Block 1A introduced a new computer system to counter more maneuverable targets. The Block 1B PSuM (Phalanx Surface Mode, 1999) adds a forward-looking infrared (FLIR) sensor to make the weapon effective against surface targets. 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. The FLIR's capability is also of use against low-observability missiles and can be linked with the RIM-116 Rolling Airframe Missile (RAM) system to increase RAM engagement range and accuracy. The Block 1B also allows for an operator to visually identify and target threats.

Since the end of FY 2015, the US Navy has upgraded all Phalanx systems to the Block 1B variant. 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. The FLIR sensor improves performance against anti-ship cruise missiles, while the OGB and ELC provide tighter dispersion and increased "first-hit" range; the Mk 244 ELC is specifically designed to penetrate anti-ship missiles with a 48 percent heavier tungsten penetrator round and an aluminum nose piece. Another system upgrade is the Phalanx 1B Baseline 2 radar to improve detection performance, increase reliability, and reduce maintenance. It also has a surface mode to track, detect, and destroy threats closer to the water's surface, increasing the ability to defend against fast-attack boats and low-flying missiles. As of 2019, the Baseline 2 radar upgrade has been installed on all U.S. Navy Phalanx system-equipped vessels. The Block 1B is also used by other navies, such as Canada, Portugal, Japan, Egypt, Bahrain, and the UK.

In April 2017, Raytheon tested a new electric gun for the Phalanx allowing the system to fire at varying rates to conserve ammunition. The new design replaces the pneumatic motor, compressor, and storage tanks, reducing system weight by 180 lb (82 kg) while increasing reliability and reducing operating costs.

### Operation

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 (2 to 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.

The only inputs required for operation are 440 V AC three-phase electric power at 60 Hz and water (for electronics cooling). 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. It also stores data from any engagements the system conducts so that it can later be analyzed.

#### Radar Subsystems

The CIWS has two antennas that work together to engage targets. The first antenna, for searching, is located inside the radome on the weapon control group (top of the white-painted portion). The search subsystem provides bearing, range, velocity, heading, and altitude information of potential targets to the CIWS computer. This information is analyzed to determine whether the detected object should be engaged by the CIWS system. Once the computer identifies a valid target (see details below), the mount moves to face the target and then hands the target over to the tracking antenna at around 8 km. The track antenna is extremely precise, but views a much smaller area. The tracking subsystem observes the target until the computer determines that the probability of a successful hit is maximized and then, depending on the operator conditions, the system either fires automatically at around 2 km or recommends fire to the operator. While firing 75 rounds per second, the system tracks outgoing rounds and 'walks' them onto the target.

#### Gun and Ammunition System

The Block 0 CIWS mounts (hydraulic driven) fired at a rate of 3,000 rounds per minute and held 989 rounds in the magazine drum. The Block 1 CIWS mounts (hydraulic) also fired at 3,000 rounds per minute with an extended magazine drum holding 1,550 rounds. The Block 1A and newer (pneumatic driven) CIWS mounts fire at a rate of 4,500 rounds per minute with a 1,550-round magazine. The velocity of the rounds fired is about 3,600 feet per second (1,100 m/s). The rounds are armor-piercing tungsten penetrator rounds or depleted uranium with discardable plastic sabots. The Phalanx CIWS 20–mm rounds are designed to destroy a missile's airframe and make it non aerodynamic, thus keeping shrapnel from the exploding projectile to a minimum, effectively keeping secondary damage to a minimum. The ammunition handling system has two conveyor belt systems. The first takes the rounds out of the magazine drum to the gun; the second takes empty shells or unfired rounds to the opposite end of the drum.

The 20–mm APDS rounds consist of a 15 mm (0.59 in) penetrator encased in a plastic sabot and a lightweight metal pusher. Rounds fired by the Phalanx cost around $30 each and the gun typically fires 100 or more when engaging a target.

#### CIWS Contact Target Identification

The CIWS does not recognize identification friend or foe, also known as IFF. The CIWS has only the data it collects in real time from the radars to decide if the target is a threat and to engage it. A contact must meet multiple criteria for the CIWS to consider it a target. These criteria include:

1. Is the range of the target increasing or decreasing in relation to the ship? The CIWS search radar sees contacts that are out-bound and discards them. The CIWS engages a target only if it is approaching the ship.
2. Is the contact capable of maneuvering to hit the ship? If a contact is not heading directly at the ship, the CIWS looks at its heading in relation to the ship and its velocity. It then decides if the contact can still perform a maneuver to hit the ship.
3. Is the contact traveling between the minimum and maximum velocities? The CIWS has the ability to engage targets that travel in a wide range of speeds; however, it is not an infinitely wide range. The system has a target maximum-velocity limit. If a target exceeds this velocity, the CIWS does not engage it. It also has a target minimum-velocity limit, and does not engage any contact below that velocity. The operator can adjust the minimum and maximum limits within the limits of the system.

There are many other subsystems that together ensure proper operation, such as environmental control, transmitter, mount movement control, power control and distribution, and so on. It takes six to eight months to train a technician to maintain, operate, and repair the CIWS.