The contract package for five of the rapid-fire 20mm weapons systems is worth about $68 million. Deliveries are to begin next year.
"Phalanx provides unparalleled ship self-defense to fleets operating in blue water as well as littoral environments," said Rick Nelson, vice president of Raytheon Missile Systems' Naval and Area Mission Defense product line.
"Thanks to its array of sensors, Phalanx brings a proven solution against threats launched from land, sea or air."
Phalanx is a radar-controlled, Gatling gun system that automatically acquires, tracks and destroys threats that have penetrated other defense systems. It is capable of firing more than 4,000 rounds a minute and has an effective range of 2.2 miles.
Raytheon, which announced the contract at the Euronaval 2012 exhibition in France, said more than 890 systems have been built and deployed in the navies of 25 countries.
"The addition of these five systems underpins the Royal Navy's Fleet 2020 capability plans and significantly increases ship self-defense to crews and ships," said Paul Gilligan, head of strategic programs for Raytheon UK. "The constant evolution of the threat demands the most successful and reliable method of protection, which Phalanx provides."
Installation of the systems, as well as in-service support, will be provided by Britain's Babcock Marine.