Gumdoksuri-class

The Republic of Korea Navy initiated the PKX (Patrol Killer eXperimental) development program in 2003. This modernization project followed the loss of a Chamsuri-class patrol boat during a 2002 naval engagement with North Korean vessels. The program produced two distinct designs: the PKX-A, also known as the Yoon Youngha-class, and the PKX-B.

The PKX-A is a missile-armed vessel designed to perform operations formerly conducted by Pohang-class corvettes. The PKX-B is a smaller, gun-armed variant developed to replace the aging Chamsuri-class fleet. Both designs utilize combined diesel and gas (CODAG) propulsion systems driving waterjets. The PKX-B is specifically configured to counter fast swarming craft and features a stern-mounted guided rocket launcher. These rockets employ GPS/INS midcourse guidance with data uplink and terminal imaging infrared homing. Sensor and processing systems across the class include 3D surveillance and surface search radars, fire control radars, and electro-optical targeting systems. Electronic warfare capabilities include an ECM/ECCM suite and chaff/flare dispensers.

Construction of the class was divided between Hanjin Heavy Industries and STX. The lead ship of the PKX-A variant, Yoon Youngha, was launched in 2007 and entered service in 2008. The Republic of Korea Navy named the first six ships of the PKX-A variant after sailors killed in the Second Battle of Yeonpyeong. The PKX-A series reached its planned total of 18 active vessels. The first PKX-B vessel entered service in late 2017. As of the current reporting, 16 PKX-B vessels are active, with additional units planned for delivery. In assigning pennant numbers, the Republic of Korea Navy omits the digits '0' and '4' due to cultural beliefs regarding bad luck, with specific exceptions made for other vessel types.