[3] 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.

When the electrification of rail lines in Korea was begun in 1943, Sentetsu ordered twenty DeRoI class locomotives of 135 tons - sixteen from Toshiba[6] and four from Mitsubishi.

[4] At the time of the partition of Korea after the end of the Pacific War, of the five Toshiba-built DeRoI class locomotives, four were in the North and one was in the South, in Seoul for repairs.

[6] After the partition, the Allied General Headquarters (GHQ) in Tokyo ordered the delivery of three Mitsubishi-built and seven Toshiba-built DeRoI class locomotives to Korea as reparations; these were all delivered to the South.

[11] DeRoI 6 had been completed in November 1944 and taken to the port at Kobe, Japan, for delivery, but was subsequently returned to the factory; this became the first of the ten new locomotives to be delivered to Korea, in March 1946.

In that year they were reclassified Chŏngiha (전기하) class and numbered 전기하1 through 전기하9, 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.

[12] Originally painted brown, they were repainted in 1958-59 in the light blue over dark green livery to match the scheme that was made standard with the introduction of the Red Flag 1 class electric locomotives.