Loran-C is one of the LOng RAnge Navigation systems that was operated by the US (Air Force), was acquired by South Korea's Ministry of Oceans and Fisheries in 1979, and operated by the latter since 1989.

In Loran-C, one master station and two to four secondary stations form one chain. It uses the hyperbolic navigation method that is widely used in various fields for ships, land transports, and aircraft. It uses the radio signal arrival time difference between the master station and secondary stations to measure the position.

The range of usage is about 1,200 miles (2,200 km). In South Korea, the Korea Loran-C Chain (GRI9930) was established to provide position information to users, with Pohang serving as the master station and Gwangju and Ussuriysk, Russia as secondary stations.