When Sentetsu decided to electrify the line between Pokkye and Gosan in 1940, they ordered Mitsubishi to develop a new type of modern electric locomotive. This was the first time on Japanese-controlled territory that a line was electrified with 3,000 Volts DC and using regenerative braking. The locomotives were similar to the Japanese EF12 and stood on two bogies with three driving axles and one leading axle each. They were designated DeRoI, where the “De” stood for “electric”, the “Ro” stood for six driving axles and the “I” stood for the first design of this layout (“ichi” = “one”).

16 locomotives were built by several manufacturers, although it is hard to find out which company built how many. The first four were assembled in 1943 by Kisha Seizō, with electric equipment by Toshiba. Toshiba themselves completed more locomotives from 1944. Two or three were built by Mitsubishi in 1946. All these were nearly identical and had six traction motors with 385 kW each. Two locomotives were powerful enough to haul a freight train of 1,200 tonnes over the mountain pass on the Pokkye-Gosan line with 42 km/h. The variant built by Hitachi had traction motors with only 350 kW and had different air compressors and fans. It was designated DeRoNi, where the “Ni” stood for “two”.

Around ten went to North Korea either upon the separation of the country or were captured in the war. There they were in storage until 1956 while the overhead lines were repaired. When they were put into service again, the three variants were designated Chŏngiha, Chŏngidu and Chŏngisŏ, where the suffixes stood for the variants one, two and three. All which were remaining in the south were scrapped. In the north, at least one was still operational in 2011.