While the program seems not yet to have approved funding, the military is proposing it as a response to North Korea's submarine force. A North Korean submarine torpedoed and sank the South Korean corvette Cheonan in March 2010; 46 sailors died. North Korea has about 70 submarines, according to a South Korean board of inquiry report. Although mostly small and all rudimentary, as diesel-electric submarines they are hard to find when submerged.
South Korean warships detected only 28% of North Korean submarines that exercised in the first quarter of 2010, Shin Hak-yong, a Democratic member of the National Assembly's Defense Committee, told the Chosen Ilbo newspaper in 2011. The performance of the P-3CKs in detecting North Korean submarines was not discussed. South Korea is reportedly installing a fixed underwater acoustic-detection chain, similar in principle to the U.S. Navy's Cold War Sosus. Aircraft like P-3s are used as interceptors, prosecuting contacts from the fixed sensors.
The estimated budget for new maritime aircraft is 1 trillion won ($900 million), which will certainly not cover 20 Poseidons nor even SC-130Js, whose design is offered by Lockheed Martin as a maritime development of the C-130J Hercules transport. So if more money is unavailable, the C295 will be a strong candidate.
If the South Korean navy is serious about the Poseidon, then it is probably raising concerns about Japan as well as North Korea. “Japan's defense posture is a consideration in South Korean defense planning that outside observers often greatly underestimate,” says Tim Huxley of the International Institute for Strategic Studies in Singapore. Japan revealed in 2010 that it would increase its submarine force to 24 vessels from 18, including two assigned to training, apparently in response to growing Chinese assertiveness and naval strength.
China's fleet of full-size submarines is by far the largest in Asia, but Huxley doubts that the giant neighbor features significantly in South Korea's threat perceptions.
With Bill Sweetman in Washington.