A year ago, South Korean media were reporting about government sources leaking news that a new cruise missile, with a range of 1,000 kilometers, was in production. Now the leaks indicate that the missile was actually deployed earlier this year. The missile, called Hyunmoo 3, was first reported three years ago. The latest leaks describe the Hyunmoo 3C missile as having a range of 1,500 kilometers, and being deployed along the North Korean border, aimed at ballistic missile, nuclear weapons and other strategic targets to the north.
For the last 30 years, 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. South Korea belongs to the Missile Technology Control Regime (MTCR), and thus agrees 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.
Four years ago, South Korea announced that it had developed a cruise missile, the "Cheon Ryong," that was similar to the American Tomahawk, but with a 500 kilometer range and a half ton warhead. This was not unexpected. The U.S. had to apply a lot of pressure on South Korea in the 1990s, to stop production of ballistic missiles. The South Koreans eventually backed off on this, despite the hundreds of ballistic missiles North Korea had built, and aimed at them. But the shift in policy wasn't completely because of American pressure. The South Koreans realized that cruise missiles would be cheaper, and just as effective, as ballistic missiles. South Korea had the technology to build good cruise missiles, and a lot of them. Not a lot of details were released on the "Cheon Ryong," but it was small enough to be fired from a torpedo tube. That means a six meter long missile, with a diameter of about 500mm, and weighing about 1.2 tons. Such a missile could be built for about $1-2 million each, which enables you to build about five cruise missiles for the price of one ballistic missile.
Of course, the main reason for using ballistic missiles is because they are difficult to intercept. In theory, a cruise missile is detectable, and as vulnerable as an aircraft. But in practice, South Korea has long had the technology, and capability, to build a cruise missile that can fly low (under 66 meters/200 feet) and avoid detection by radar. South Korean knows a lot about the North Korean air defense system, which is decidedly low tech (although quite massive) compared to what South Korea has. Actually, the low tech aspect (lots of human spotters and elderly anti-aircraft guns) is the biggest danger the cruise missiles will face heading north. But the South Koreans know that, and the cruise missiles can carry cluster bomb payloads for attacking the anti-aircraft guns that cannot be flown around. Still, while the cruise missiles may be able to avoid anti-aircraft missiles, it's going to have a harder time with all those bullets. But a cruise missile can be more accurate than a ballistic missile, and come in at different angles. That will be useful in taking out the many underground bunkers up north, or at least the entrances.
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.