South Korea recently conducted a successful test of a locally made ballistic missile with a range of 500 kilometers. This enables South Korea to hit targets anywhere in North Korea with weapons (ballistic missiles) that North Korea is not equipped to stop. This test ends decades of restrictions on South Korean ballistic missile development.
Until 2012 South Korea and the United States had an agreement that limited South Korean made ballistic missiles to 300 kilometers range. In return the United States pledged prompt and substantial military support in the event of an attack by North Korea. In 2012 that treaty was modified because of growing aggression by North Korea and a rapidly growing North Korean arsenal of ballistic missiles. The 2012 amendments allow for South Korean missiles with a max range of 800 kilometers. The original restrictions were a gesture to North Korea in n effort to halt a ballistic missile arms race. By 2012 it was clear that the north wanted nothing to do with ballistic missile restrictions. Meanwhile South Korea has over two decades experience developing satellite launchers and military ballistic missiles. South Korea is better equipped (with tech and manufacturing capability) than North Korea to develop and build ballistic missiles and satellite launchers. So the 2012 amendments to the ballistic missile agreement were expected to show quick results.
Back in 2012 the South Korean military also called for over $2 billion to be spent on missiles during the next five years. This plan was largely approved. This was part of an effort to develop the capability to quickly weaken the North Korean artillery and missile forces in any future war. The South Korean plan included the purchase of over a thousand new ballistic and cruise missiles. These are aimed at specific North Korean missile launchers and artillery positions. In the event of a war, the South Korean missiles can be quickly launched and most North Korean missile and artillery weapons destroyed. That would mean less destruction in South Korean territory. The North Korea plan had always been to start any future war with an enormous bombardment of South Korea using shells, rockets, and missiles. Most would be aimed at the South Korean capital, and largest city, Seoul.
Nearly all the $2 billion was spent on missiles made in South Korea. At the same time the government also revealed the existence of some of these locally developed missiles. This included a new cruise missile and ballistic missile that were ready for service. South Korea is usually secretive about its battlefield missiles although some details do leak. In 2009 South Korean media reported that a new cruise missile, with a range of 1,000 kilometers, had secretly entered production in 2008. The missile, called Hyunmoo 3, has since been superseded by the Hyunmoo 3C missile, which has a range of 1,500 kilometers and is being deployed along the North Korean border, aimed at ballistic missiles, nuclear weapons, and other strategic targets to the north.
Since the 1980s the United States has been discouraging South Korea from developing long range ballistic and cruise missiles. Despite the U.S. refusal to help, South Korea developed a 180 kilometer range ballistic missile (Hyunmoo 1) and a 300 kilometer one (Hyunmoo 2) in the 1980s. Both are about 13 meters (40 feet) long and weigh 4-5 tons. By 2001 South Korea accepted the Missile Technology Control Regime (MTCR) and thus agreed not to build ballistic missiles with a range of more than 300 kilometers. Hyunmoo 1 and 2 used a design based on that of the U.S. Nike-Hercules anti-aircraft missile, which South Korea used for many years.
Cruise missiles are simpler technology, and apparently the Hyunmoo 3 is made entirely with South Korean developed components. Like the Tomahawk, Hyunmoo 3 appears to be about 6 meters (19 feet) long, weighs 1.5 tons, has a half ton warhead, and is launched from hidden (in the hills facing North Korea), and probably fortified, containers. North Korea has about 600 ballistic missiles aimed at South Korea.
The longer range of the Hyunmoo 3C enables it to hit any target in North Korea and is apparently intended to knock out transportation and supply targets deep inside North Korea. With a range of 1,500 kilometers the missile could also hit targets in China and Russia.
Meanwhile in 2011 South Korea moved some of its ATACMS (Army Tactical Missile Systems) guided missiles close to the North Korean border. ATACMS is a 610mm rocket that fits in the same size container that normally holds six 227mm MLRS rockets. The ATACMS version in South Korean service has a range of 165 kilometers. That makes it capable of reaching many targets in North Korea but not the capital (Pyongyang, which is 220 kilometers north of the DMZ). There is a version of ATACMS with a range of 300 kilometers but South Korea did not have any. ATACMS is fired from the American MLRS rocket launcher. South Korea only has 220 ATACMS missiles. All of them have cluster bomb warheads. Half of them are unguided and have a range of 128 kilometers. The others have smaller warheads, GPS guidance, and a range of 165 kilometers. This is apparently the version moved close to the border, in order to make the North Koreans nervous. South Korea originally bought ATACMS in 1998, to have a weapon that could go after distant North Korean artillery and large concentrations of tanks.
Despite American opposition South Korea began developing, but not mass-producing, ballistic missiles in the 1970s. South Korea certainly has the technical expertise and manufacturing capability to produce a more modern ballistic missile with a range of 300 kilometers, as was shown in the recent video. South Korea has signed an international treaty agreeing to not build ballistic missiles with a range greater than 300 kilometers but public opinion in the south is calling for that limit to be broken, in order to make all of North Korea vulnerable to ballistic missile attack from the south. It's possible that some of South Koreas newly revealed ballistic missiles can actually go farther than 300 kilometers and are only limited by restrictions programmed into the missile guidance system. This software could be quickly changed.
At this point the United States is no longer trying to restrict South Korean missile development. The South Koreans tried for over a decade to develop warmer relations with North Korea and all efforts failed. The 2010 North Korea attacks (using artillery and a torpedo than sank a warship) on South Korea changed a lot of attitudes in South Korea, and the United States. North Korea is still a big problem but now South Korea is free to try whatever it thinks will work.