North Korea appears to have upgraded its KN-01 anti-ship missile to create a version with a range of over 300 kilometers, twice the range seen in previous versions. The KN-01 is based on the Chinese Silkworm anti-ship missiles which are, in turn, based on a 1950s Russian design. Most of the North Korea anti-ship missiles are fired from fixed and mobile launchers on land.
The two ton Silkworm didn't enter service until the 1980s, and is still found in the arsenals of nations who can't afford the more modern stuff. The Silkworm looks like a small jet fighter, without a cockpit. The first versions had a range of about 90 kilometers and were effective against modern warships that had not turned on their defenses. North Korea normally buys older models of weapons cheap and then upgrades them. Guidance systems are a problem with North Korean missiles, since these require more cash and tech than is available, but the North Koreans are believed to have improved the guidance on the KN-01 in addition to its rocket motor.
With the longer range comes a need for target acquisition and location systems. The new KN-01 will rely on aircraft (less likely) or submarines (more likely) to radio back location data for targets. The longer range KN-01s (usually several or even a dozen or more if the target is a carrier) will then be programmed with locations and depend on their new terminal guidance systems to find the ships. North Korea may also have some counter-measures for electronic missile defense carried by many ships.