March 27, 2013:
On the third anniversary of a North Korean sub torpedoing a South Korean Pohang class corvette, South Korea finds that it is no better prepared to deal with torpedo attacks by North Korean mini-subs than it was in 2010. That’s because fixes that would work could not be done in a hurry.
What South Korea needed was a better way to detect the small North Korean subs. The Pohang class ships were equipped with sonar that could detect such small subs about two kilometers (2,000 meters) away. New sonar that could detect these subs up to 15 kilometers away was not immediately available. Meanwhile a replacement for the Pohang class ships was on the way, the first one of these Incheon class frigates entered service two months ago.
Another solution was an underwater sonar array, like the American SOSUS system used during the Cold War. This could be installed but for it to work you needed several years of using it to listen to the subs and surface ships (and large sea creatures) that frequent the coasts in order to establish who was who and what was what. That process is now under way and it will be another year or two before the SOSUS is useful.
While the Pohangs were built for anti-submarine warfare, they were only really effective against the 20 or so larger ocean going North Korean subs. These are all elderly, noisy boats, which rarely went to sea. Most of North Korea's 90 subs are much smaller than the ocean going ones and operate along the coast. These shallow waters have more currents and a lot more underwater noise. The Pohang's sonar, while adequate on the high seas against noisy older boats, is very inadequate close to the shore. Orders were immediately given to install 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 and 1993 24 Pohangs were put into service. So far, one has been retired and one (Cheonan) has been sunk. The remaining Pohangs are due to wear out soon. The 2,300 ton Incheon class frigate is replacing the Pohangs, but these are only being built at the rate of one or two 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. These defenses are of limited effectiveness. For the moment, the Pohangs are as vulnerable as they were three years ago.
South Korean efforts to install underwater submarine sensors off its coasts were more successful, although few details were revealed. It is known that the technology is similar to what the U.S. used for its SOSUS systems during the Cold War. SOSUS systems are very expensive to maintain. The American SOSUS managed to survive the end of the Cold War by making its sensors available for civilian research and by using cheaper and more powerful electronic and communications technology. While many parts of the SOSUS have been shut down, additional portable SOSUS gear has been put in service, to be deployed as needed. This is apparently the technology South Korea had access to.
South Korea also appears to have obtained help in making their sonars more effective. The U.S. has been doing research in this area and apparently offered to help. South Korea also has the design and manufacturing capability for this sort of device. The first South Korean SOSUS system was placed off the west coast, near the North Korean border. North Korean submarines, travelling under water, using battery power and near the coast, are very hard to detect. The South Korean SOSUS will help even the odds.