The first electrified railway in Korea was the 29.7 km (18.5 mi) 1,067 mm (42.0 in) narrow gauge streetcar line in Seoul running from Seodaemun to Cheongnyang-ni via Cheongno and Dongdaemun, which was opened on 18 April 1898 by the Hanseong Electric Company.

[3] The Government-General of Korea began working on a national electric power policy in November 1926, and the resulting plan was completed in December 1931.

[3] Sentetsu issued its requirement for an electric locomotive in 1938, beginning discussions with Mitsubishi in that year regarding the implementation of the electrification plan.

Part of the Railway Bureau's goal with the electrification plan was to set a new world speed record, and to go with that, a state-of-the-art locomotive was desired.

When the electrification of rail lines in Korea was begun in 1943, Sentetsu ordered twenty DeRoI class locomotives of 135 tons - sixteen from Toshiba[5] and four from Mitsubishi[4] The original class name, デロイ (DeRoI), comes from the Sentetsu classification system for electric locomotives: DeRoI = De, for "electric" (from 電気, denki), Ro, to indicate six powered axles (from Japanese roku, 6), and I (from Japanese ichi, 1), indicating the first class of electric locomotive with six powered axles.

[11] In that year they were reclassified Chŏngisŏ (전기서, "Electric-3") class and numbered 전기서1 through 전기서3, and were refurbished at the engine shops at Yangdŏk for use on the Yangdŏk-Ch'ŏnsŏng section of the P'yŏngra Line, which had been electrified in 1956 as the first stage of North Korea's electrification plans.