[1] The first rail line to reach Susŏng was the Ch'ŏngjin−Ch'angp'yŏng section of the Hamgyŏng Line, opened by the Chosen Government Railway (Sentetsu) on 5 November 1916.

On 31 July 1917, the management of Sentetsu was transferred from the Railway Bureau of the Government-General of Korea to the South Manchuria Railway (Mantetsu).

Under Mantetsu management, construction of the Hamgyŏng Line was accelerated, and to handle increasing freight traffic on the line, a large marshalling yard, called Ch'ŏngjin Choch'ajang, was built near Ch'ŏngjin.

[1] To access this, a new 14.9 km (9.3 mi) line between Ranam and Susŏng was opened on 10 December 1919; Kangdŏk Station, located 7.2 km (4.5 mi) from Ranam, was opened on 1 August 1922.

The existing line, running via Kangdŏk and the marshalling yard, was detached from the Hamgyeong Line and designated the Kangdŏk Line; at the same time, a 2.4 km (1.5 mi) connection from Ch'ŏngjin Sŏhang Station (Ch'ŏngjin West Port, today called Songp'yŏng) to Kangdŏk was built, to allow southbound trains to access the marshalling yard without having to reverse at Ranam.