Last ditch defence – the Phalanx close-in weapon system in focus

The ubiquitous Phalanx close-in weapon system (CIWS) provides warships a last line of defence against missiles, aircraft and small boats. Upgraded over time, it has been in service for 38 years with the Royal Navy. Here we look at the history, design and capabilities of this system.


Development of the Vulcan Phalanx began in the 1960s as the US Navy woke up to the threat of the sea-skimmers after the destruction of Israeli destroyer Eilat by Russian-made Styx missiles in 1967. The M61 Vulcan Gatling gun had been in service since 1959 and was initially developed for use in air-air combat. Using a Gatling gun combined with radar in the close air defence role to create a ‘wall of steel’ offered a relatively simple solution. In parallel, the US Army pursued a similar idea, producing the tracked vehicle M163 Vulcan Air Defense System (VADS).

The first Phalanx prototype was installed on destroyer, USS King, in 1973. Substantial development and trials were needed before the Mk-15 Phalanx went into full production in 1978 with USS Coral Sea taking the first operational Block 0 mounts to sea in 1980. In the late 1970s, the RN was also aware of the threat from sea skimmers and the GWS-25 Sea Wolf Point Defence Missile System was seen as the answer. Unfortunately, Sea Wolf was expensive, had a large equipment footprint and had only been fitted to a handful of frigates when the Falklands war unexpectedly erupted in April 1982. HMS Sheffield and MV Atlantic Conveyor were lost and HMS Glamorgan badly damaged by Exocet missiles. Other ships were hit during low-level bomb attack and the lack of close-in defensive capability was badly exposed. The loss of HMS Coventry in particular also demonstrated the fallibility of missile systems, even if a PDMS is present a more potent CIWS could provide a last-ditch backup.

In the 1970s RN could have argued that it was primarily an ASW navy, and had not prioritised close-in defence for the surface fleet. It is sobering to contemplate how warships, who’s CIWS and PDMS mostly amounted to a couple of old Oerlikon 20mm or Bofors 40mm cannons and obsolete Sea Cat missiles might have fared in the Norwegian Sea, GUIK or North Atlantic against a hail of Soviet anti-ship missiles.

  • (Left) USS King carried the first prototype Vulcan Phalanx to sea in 1973. (Right) The first mount in RN service (Block 0) seen on the foredeck of HMS Illustrious, Dec 1983.

  • Rapidly up-armed in light of painful experience, HMS Illustrious with the first two Phalanx mounts in service with the RN departs the Tyne, June 1982. Illustrious was rushed into service to provide reinforcements for the Falklands War. (Photo: Rosedale7175)

  • Note the addition of the barrel restraint of block 1A mount (HMS Edinburgh, July 2011)

  • Beginning in 2006, the RN’s inventory was gradually upgraded to Block 1B standard. Note the strengthened barrel restraint and muzzle brace to support the longer barrels and the Infra-Red camera on the left side. (Live firing, HMS Albion, October 2019)

  • (left) Goalkeeper shoot (HMS Invincible, 2003). On paper, the more capable system but Goalkeeper never achieved the global sales success of the lighter/simpler Phalanx competitor which benefits from a large userbase and logistic support together with continuous development. Over 1,000 units have been manufactured and many have cycled through upgrade programme more than once.

  • Counter-Rocket, Artillery, Mortar (C-RAM) Intercept Land-Based Phalanx Weapon System (LPWS). The 30 systems employed by the US in Iraq had defeated over 100 missile and mortar attacks by 2008. The British Army deployed LPWS to protect Basra Airport, Iraq in 2007. 5 units were initially leased from the US Army but later replaced by units converted by Raytheon from the RN’s Phalanx inventory. They were all eventually returned to the RN and converted to 1B standard. (Photo: USAASC)

  • Although Raytheon manufactures the system in the US, the Royal Navy’s mounts are serviced and upgraded under a rolling contract with Babcock at their facilities in Devonport Dockyard.

  • (Left) With the radome removed the rotating search radar can be seen on the top of the mount. The parabolic tracking radar can be seen below. (Right) the 6-tonne mounts moved around the workshop by gantry crane.

Retro-fitting Sea Wolf to RN warships was neither affordable or practical whereas the Phalanx offered an immediate remedy. Being self-contained, one of Phalanx’s key selling points is being non-deck penetrating – it can simply be bolted to the deck of any ship with space and top weight margin. While the Falklands war was still in progress, two Phalanx systems intended for the USN were taken off the production line and rushed to Tyneside where HMS illustrious was hastily being completed. Phalanx was first tested at sea by Illustrious on 20th June and again on 26th June, destroying the Rushton target with the first burst of fire. Although the Argentines surrendered on the Falklands Islands on 14 June, hostilities had not formally ceased. Equipped with Phalanx, the ship sailed south with greater confidence that an Exocet attack on the carrier could be defeated.

Phalanx has remained in RN service ever since 1982. It was fitted to the Invincible class carriers, HMS Fearless, HMS Ocean and the QEC class carriers. The Type 42 air defence destroyers received the system and also their replacements, the Type 45s. Units are also fitted to Royal Fleet Auxiliary vessels, being rotated around ships as operational requirements dictate. The self-contained nature of Phalanx makes it particularly useful for self-defence of large, vulnerable auxiliaries that lack their own sensors and combat systems.

In return for the Dutch Navy purchasing UK-made Spey gas turbines, the RN later also adopted the Hollandse Singnaalapparaten (now Thales) Goalkeeper 30mm CIWS for some vessels between 1988-2015. The Goalkeeper system has the advantage of heavier rounds and almost twice the effective range of the original Phalanx, able to break up an incoming missile further way from the ship. The through-life costs of the larger Dutch system were higher as it was deck-penetrating, limiting which vessels could carry the mount. The system was gradually withdrawn from RN service, the last mount removed from HMS Bulwark in 2016. Sister ship HMS Albion now carries Phalanx, which has benefited from an on-going development programme in a way that Goalkeeper has not.


As missile technology evolved, Raytheon has developed the Phalanx System in response. The original Block 0 system could take two men as long as 30 minutes to reload from pre-linked ammunition boxes. Block 1 increased ammunition capacity from 990 to 1,550 rounds and a new preloaded ammunition loader/unloader cart dramatically reduced reload time to 5 minutes. The Block 1/Baseline 0 (1988) featured better radar to detect a new generation of smaller supersonic anti-ship missiles. B1 Baseline 1 raised the rate of fire from 3,000 rounds per minute to 4,500. B1 Baseline 2 (1991) improved accuracy with an improved muzzle restraint to decrease round dispersion. Block 1A (1996) introduced a new computer system to counter high diving and hard manoeuvring missiles and switched from hydraulic to pneumatic gun drive which could spin up faster.

The Block 1B upgrade PSuM (Phalanx Surface Mode) launched in 1999 was the most significant update so far, a response to navies increasingly operating in the congested littoral areas. The primary counter-missile capability was enhanced to defeat fast inshore attack craft (FIAC), helicopters, UAVs, USVs and small stealthy missiles, difficult to detect on radar. The solution was the addition of electro-optical thermal imaging technology to supplement the radars. The stabilised Forward-Looking Infra-Red (FLIR) camera is mounted on the left side of the radome also allows the operator to visually identify targets in complex environments.

The original M61A1 gun barrels were designed for short bursts and dispersion increased with barrel wear. The B1B remedies this with thicker Optimised Gun Barrels (OGB), their length has been increased from 1.520m to 1.981m and they are supported by the distinctive cage muzzle brace for further accuracy gains. B1B fires the slightly modified Mk 244 Mod 0 ELC (Enhanced Lethality Cartridges) featuring a 48% heavier tungsten alloy penetrator over the older Mk 149 rounds.

Warship/Auxiliary Total mount positions Mounts fitted (Aug 2020)
2 x Queen Elizabeth Class Carriers 6 5
2 x Albion Class LPDs 4 2
6 x Type 45 Destroyers 12 6
3 x Bay Class RFA 6 4
4 x Tide Class RFA 8 2
RFA Fort Victoria 2 0
2 x Wave Class RFA 4 0
2 x Fort class RFA 4 0
TOTAL 46 19
8 x Type 26 Frigates (from 2027) 16
3 x Fleet Solid Support Ships (?) 6
2 x Littoral Strike Ships (?) 4


Through a rolling procurement programme, the RN had accumulated 36 mounts by 2001 which comprised a mix of Block 1 (Baseline 2) and Block 1A. In 2006 Babcock were awarded a £35 million contract to convert 16 of these mounts to B1B standard, using kits supplied by Raytheon. Subsequently, an additional 8 units were upgraded and in 2012 a further 5 new B1B mounts were purchased directly from Raytheon, primarily intended for RFAs. In 2014 Babcock received a contract to upgrade a further 4 units. There are at least now 41 mounts in the RN inventory and at least 33 of them are B1B standard. Units are rotated between warships in refit and RFAs not deploying to high threat areas, providing for planned maintenance, as the table above indicates, there are sufficient numbers for the RNs requirements.


In action

Phalanx was one of the world’s first fully autonomous weapons, the speed of anti-ship missiles demands a system able to react fully automatically without human intervention. When in Auto mode, the rotating MTI search radar in the top of the mount continually scans for threats up to 15 Km away (Although, rotating through 360º the radar is switched on and off by software to prevent irradiation of the ship’s superstructure). For simplicity Phalanx does not rely on sophisticated IFF transponder systems for target discrimination, instead, every contact is assessed using closed-loop heuristic software. If the target is inbound, able to manoeuvre to hit the ship, and moving at a pre-determined minimum speed then it will be engaged. Once confirmed as hostile, the contact is passed to the tracking radar which locks on at about 8 km range.

When the target is about 2km away from the ship, the gun opens fire. 75 rounds per second leave the barrel at a velocity of 1,113 meters per second. The tracking radar compares both the target and the stream of outgoing rounds, adjusting the gun so the projectile stream converges on the target. Accuracy is such that typically the third round out of the barrel will hit. The system will consider the target destroyed if it explodes or there is an abrupt change of speed and direction as the target’s airframe breaks up. In the event of multiple attacks, the next most imminent threat will immediately be engaged. The system can track and assess up to 6 targets simultaneously. After an engagement, two sailors will re-load the ammunition drum at the earliest opportunity.

The gun is fully trainable with a horizontal arc of 300º, the expectation being that usually at least two mounts will be installed per ship for overlapping 360º coverage. The B1B can be trained to point low to engage small boat targets down to -25° or point almost vertically up at +85° to engage diving targets. Smooth and accurate servo motors can rapidly train and elevate the gun by at up to 115º per second in both axes, making it almost impossible to outmanoeuvre. When the mount is installed in the ship, a series of hard stops are used to limit the arcs to prevent rounds hitting the ship’s decks or superstructure.

  • Phalanx in action. Note washer fluid tank used with the screen wiper to clean the camera lens clean (Photo: US Navy).

  • Phalanx control console in the operations room. Local control from the mount is also possible. (HMS Edinburgh, 2012)

  • The forward mount being fitted to RFA Tidespring in Cammell Laird shipyard. The gun barrels are removed and the radome assumes the horizontal position protected by a cap for transport and installation. (Sept 2019)

  • Maintainers load ammunition (HMS Albion).

  • Weapon engineers of 1700 Naval Air Squadron are assigned to the Royal Fleet Auxiliaries to maintain aircraft and self-defence weapons. Phalanx requires a chilled water supply for electronics cooling and a 440v/70Kw electrical supply from the ship. Other than ammunition lockers, the impact on the ship is minimal. (RFA Tidespring, April 2020)

  • The Mark 244 Mod 0 Armour-Piercing Discarding Sabot (APDS) 20mm round. The ELC (Enhanced Lethality Cartridges) feature a heavier tungsten alloy penetrator. (Images: General Dynamics Ordnance and Tactical Systems)

  • Rounds being loaded. The orange discarding sabots are clearly visible. (HMS Southampton, May 2007)

The RN has never fired Phalanx in anger although it has provided reassurance to crews during many operations. Despite being proven during multiple tests and trials the system has had a slightly unlucky history. Most notably Phalanx did not fail but was simply switched to standby when USS Stark was hit by two air-launched Exocets fired by an Iraqi Mirage jet in March 1987. During the first Gulf war in 1991, the Phalanx onboard USS Jarret in automatic mode fired at a chaff cloud launched by USS Missouri in response to an attack by an Iraqi Silkworm missile. Several rounds hit Missouri, fortunately without causing casualties and the Silkworm was destroyed by a Sea Dart fired by HMS Gloucester. In June 1996, the Phalanx-equipped Japanese destroyer Yugiri accidentally shot down a USN A6 Intruder that was towing a radar target during a joint gunnery exercise. It was determined the operations team on the destroyer opened fire before the aircraft was outside of the Phalanx’s engagement envelope.

Hero or villain?

Gun-based CWIS has its limitations when faced with the increasing speeds of modern missiles such as BrahMos, Sunburn or Zircon. Their speed makes them harder to detect and track but it is their vast kinetic energy that is particularly deadly. Assuming the CIWS manages to break up the missile somewhere under 1km before impact, then the ship may still be sprayed with high-velocity fragments. This is obviously preferable to the intact missile impacting and detonating deep inside the ship but deadly fragments are likely to disable delicate sensors and penetrate the light steel plate of modern warships. Phalanx may prevent the loss of the ship but may not be able to stop it from becoming eliminated as an effective fighting unit. It will always be preferable for a PDMS to destroy the inbound missile well outside the Phalanx range and much further away from its intended target.

Phalanx is likely to be very effective against any aircraft that managed to get within its operating envelope but this is an increasingly unlikely scenario in an era of stand-off weapons. The system is also theoretically capable of tracking and engaging ’traditional’ ordnance such as laser-guided bombs or medium calibre shells but these are physically more robust targets and harder to penetrate and destroy, especially as modern insensitive munitions are not exploded easily. In ‘manual’ mode the phalanx operator can ‘point and shoot’ at targets indicated by the cameras. Phalanx is likely to be lethal against small, unprotected boats, USVs and UAVs, only a large ‘swarm’ attack could overwhelm it.

Amongst some naval enthusiasts, CIWS have almost become fetishised with arguments that Phalanx should be carried by virtually every vessel in the Naval Service as some kind of virility sign. In an ideal world of unlimited resources, every frontline vessel would have a complete set of equipment and not be subject to STOROB. Because each Phalanx requires weapons engineers to maintain and support the system with accompanying cost and manpower overhead, it is a sensible policy to rotate between vessels deploying to higher threat areas.

  • Phalanx HMS Prince of Wales

    The three Phalanx mounts installed on HMS Prince of Wales July-August 2020 give overlapping 360º coverage. The self-defence capabilities of the aircraft carriers draw a great deal of comment but Phalanx is just one of their many layers of protection. (Photo: S. Wenham )

  • HMS Youk Sea Ram

    At the contractor’s expense, A SEA RAM Inner-Layer Defence System (ILDS) was fitted to HMS York in place of her Port Phalanx in February 2000 and live firing trials were was completed in September 2001. The RN selected to go for the Phalanx 1B update instead. Using the same mount, to launch Rolling Airframe Missiles, SEA RAM has far greater range (10km) but is more expensive and the 11-shot launcher is challenging to reload at sea.

  • (Left) Raytheon proposed a laser co-mounted with Phalanx as a solution to the RN’s requirement for a Laser Directed Energy Weapon (LDEW) Capability Demonstrator in 2016. In the event, the stand-alone MBDA Dragonfire solution has been selected. (Right) Raytheon began consideration of a DEW version of Phalanx in 2007 with the  Laser Centurion Demonstrator for the US Army. During tests in 2009, it successfully destroyed incoming mortar rounds.

  • Initially, the LDEW is intended to provide short-range air defence, counter-UAV and close-in protection for naval vessels while the gun is retained for heavier missile targets. The attraction of the Laser is its accuracy, ability to react quickly and no requirement for ammunition. As they grow in power, theoretically targets could be destroyed at longer range and the Laser may eventually eclipse the gun and PDMS.

  • Bofors 40mm Mk 4

    2 Bofors 40mm guns will be fitted to each of the Type 31 Frigates. These non-deck penetrating mounts can deliver 5 rounds per second out to about 12.5km and are designed to respond rapidly at a wide range of elevations. By delivering heavier shells further away from the ship, in the CIWS role, the Mk 4 is superior and more flexible than Phalanx in some ways, able to use a variety of specialised munitions, depending on the target.  (Photo: BAE Systems)

When assessing the effectiveness of Phalanx, it should be seen as one part of a layered defence system. This includes intelligence-led assessments of the threat, area air defence, electronic warfare and decoys which are often overlooked or underestimated. Clearly not an infallible shield against a saturation attack by modern hypersonic missiles, Phalanx is, however, an affordable and relatively simple way to add a significant layer of protection against many threats.