May 30, 2012: South Korea has ordered eight American MH-60R Seahawk naval helicopters. These will cost $125 million each but that includes spare parts, training, and technical services. South Korea is apparently going to equip the MH-60Rs for anti-submarine work. South Korea is currently using British Lynx helicopters for anti-submarine work and is looking for replacements. Eight MH-60Rs won't replace the 23 Lynx choppers but could, if the first eight perform well.
The MH-60R is a navalized version of the 11 ton U.S. Army UH-60. The ASW version uses computers, sonar, and radar to search for submarines. This involves sailors on the MH-60Rs staring at a screen most of the time, while manipulating the sensors and computers to detect and locate subs. Once you have a solid location fix you can launch a torpedo and sink the enemy vessel.
The MH-60R uses a sonar that operates in active (broadcasting) and passive (just listening) mode. This is a dipping sonar, which is lowered into the water from the helicopter using an 806 meter (2,500 foot) cable and winch. The MH-60R is also equipped with a radar system for detecting subs on the surface or just beneath the surface (with only the periscope or snorkel, which provides air for the diesel engine and gets rid of the exhaust fumes, above the surface). The sonar system also uses sonobuoys, which are dropped and communicate wirelessly.