[3] The two sections of mainline remained isolated from each other until 18 September 1942, when the gap between Pyeongnam Gangdong and Sinseongcheon, a distance of 30.3 km (18.8 mi) was closed.

[5] The West Chōsen Central Railway nevertheless continued expanding its truncated mainline, called the Seoseon Line, receiving approval from the Railway Bureau on 21 June 1940 to extend its line to Deokcheon and thence onwards to the Jangsang coal fields,[6] in order to transport coal from the mines in the area opened in 1938 by the Chosen Anthracite Company.

However, the terrain proved too difficult, and, after adding a signal station at Hyangjang between Hyangwon and Jangsangni, construction on the current alignment of the line to Gujang began.

[10] After the end of the Pacific War and subsequent partition of Korea, the line was within the territory of the DPRK, and was nationalised by the Provisional People’s Committee for North Korea along with all other railways in the Soviet zone of occupation on 10 August 1946, becoming part of the Korean State Railway.

[12] As traffic volumes increased significantly through the Pacific War, the West Chōsen Central Railway found itself needing more power.