After the South Korean corvette Cheonan was sunk by a North Korean submarine in March, 2010, the media published a lot of information about these Pohang class warships. The most embarrassing revelation was that, although the Pohangs were built for anti-submarine warfare, they were only effective against the 20 or so Cold War era ocean going subs the North Koreans had. These are all elderly, noisy boats, which rarely go to sea. Most of North Korea's 90 subs are much smaller than the ocean going ones, and operate along the coast. The shallow coastal waters have more currents and a lot more underwater noise. Turns out that the Pohang's sonar, while adequate on the high seas against noisy older boats, is very inadequate close to the shore. Plans were made to install a more powerful sonar, but none could be found that would fit. And even if a new sonar did fit, it would weigh so much more that it would unbalance the ship.
The Pohangs are small ships. They are only 88.3 meters (290 feet) long and displace 1,200 tons. The crew of 95 operates a large number of weapons. There are four Harpoon anti-ship missiles, two 76mm cannon, two twin-40mm autocannon, six torpedo tubes (each with a Mk46 324mm/12.75 inch anti-submarine torpedo) and twelve depth charges. Max speed is 59 kilometers an hour, cruising is 28 kilometers an hour. Endurance is about ten days.
Between 1983-93, 24 Pohangs were put into service. So far, one has been retired, and one (Cheonan) has been sunk. A 2,300 ton frigate is replacing the Pohangs, but these new ships won't start entering service for another two years, and will only be built at the rate of about one a year. So for the next decade or so, the Pohangs will still be out there, providing targets for North Korean torpedoes. An attempt has been made to avoid that, by installing devices that can detect the sound of incoming torpedoes, along with acoustic (noise making) decoys that can divert the aim of some types of torpedoes. But, for the moment, the Pohangs are as vulnerable as they were a year ago.