The Phalanx Close-In Weapon System, a rapid-fire, radar and electro-optical guided gun, is designed to defeat anti-ship missiles and a range of surface threats.
It features a 20mm gun capable of firing armour-piercing bullets at up to 4,500 rounds per minute.
The Ministry of Defence has ordered the upgraded Phalanx 1B systems, which are planned to be fitted onto RFA vessels, under a £40m contract with Raytheon.
Steve Ranyard, Team Leader for the MOD’s International Guns, Missiles and Rockets Project Team, said:
This contract will help provide these Royal Navy vessels with the best possible ship self-defence 24-hours-a-day.
The Phalanx system can defend against all types of air and surface threats in the naval environment and has proved to be a reliable system on other Royal Navy ships.
Phalanx is an all-weather, day-and-night, fully automatic, self-contained weapon system that targets and engages threats under the operation of a trained Royal Navy Phalanx operator.
Phalanx 1B boasts even greater targeting ability, with an additional electro-optic infrared sensor and redesigned gun barrels.
In addition to the capability to destroy anti-ship missiles and fast jets, it can defend the ship against other threats such as helicopters and high-speed groups of gun boats.
The Phalanx system is currently installed on 14 Royal Navy vessels including the latest Type 45 destroyers.