Gumdoksuri-class

The Gumdoksuri-class patrol vessel, also designated as the Yoon Youngha-class or PKG-class, is a family of patrol ships operated by the Republic of Korea Navy of South Korea. The Republic of Korea Navy initiated development of the Gumdoksuri-class in 2003 under the Patrol Killer eXperimental (PKX) modernization program. Development was prompted by the sinking of a Chamsuri-class patrol boat during a June 29, 2002 naval clash with North Korean vessels. The program produced two variants: the larger PKX-A missile patrol ship, designed to assume roles previously held by Pohang-class corvettes, and the smaller PKX-B patrol boat, designed to replace the aging Chamsuri-class fleet.

The PKX-A variant utilizes a combined diesel and gas (CODAG) propulsion system consisting of two Hanwha Techwin/General Electric LM500 gas turbines and either Doosan/MTU 12V 595 TE90 or STX/MTU 16V 1163 TB93 diesel engines, driving three Doosan Heavy Industries waterjets. Sensor systems include an STX RadarSys SPS-100K surface search radar, an LIG Nex1 SPS-540K 3D surveillance radar, a Saab CEROS 200 fire control radar with an optronic sight, and a Hanwha Systems electro-optical targeting system. Electronic warfare systems comprise a LIG Nex1 Sonata SLQ-200(V)K ECM/ECCM suite and two T.S Tech K-RBOC Mk36 chaff/flare dispensers. Armament includes a Hyundai Wia 76 mm gun, an S&T Dynamics Nobong dual 40 mm gun, four LIG Nex1 SSM-700K Haesung anti-ship cruise missiles, and two S&T Dynamics K6 12.7 mm machine guns.

The PKX-B variant shares the CODAG propulsion, sensors, and electronic warfare suites of the PKX-A but is designed to counter fast swarming craft. Its armament consists of a Hyundai Wia 76 mm gun, two S&T Dynamics K6 12.7 mm machine guns, and a stern-mounted 12-canister 130 mm guided rocket launcher. This rocket system fires 80 kg rockets with 8 kg warheads to ranges between 3 and 20 km. The rockets use GPS/INS midcourse guidance with data uplink and terminal imaging infrared homing, and the system can fire three rockets simultaneously.

Hanjin Heavy Industries and STX Offshore & Shipbuilding constructed 18 PKX-A vessels in lots of four. The lead ship, Yoon Youngha, was launched on June 28, 2007, and commissioned on December 17, 2008. The first six ships of the subclass were named after South Korean sailors killed during the Second Battle of Yeonpyeong. The final PKX-A vessel, Jeon Byeongik, was commissioned on January 11, 2018. For the PKX-B variant, 34 vessels are planned, with 16 currently active. The lead vessel, Chamsuri-211, was launched in July 2016 and commissioned in late 2017. Subsequent PKX-B ships have been ordered from Hanjin Heavy Industries in multiple batches, extending through hull Chamsuri-229. The Republic of Korea Navy excludes the numbers '0' and '4' when assigning pennant numbers to these ships due to traditional superstition.