The Phalanx block 1B system will be installed on the lead ship of the 2,300t frigate class this year.
Phalanx is a rapid-fire, computer-controlled radar and 20mm gun system, which can automatically detect, track and destroy enemy threats.
Raytheon Naval Weapons Systems vice-president Rick Nelson said the system is capable of defending against all types of air and surface threats in the naval environment.
The new FFX ship class will replace the existing Ulsan, designed for anti-ship, anti-submarine and anti-aircraft warfare, and other smaller frigates in the ROK fleet.
South Korea is expected to sign a contract with Raytheon for an additional five Phalanx systems.