Sentetsu Tehoro-class locomotive

Having become indispensable on branchline use, it was decided to modernise the Teho type, and in 1925–26 local engineers developed a derivative locomotive.[1] The result was the テホロ (Tehoro) class, the first of which was built in July 1927 and the second in October of the same year, both at Sentetsu's Gyeongseong Works.[4] These featured a single-stage compressor, and improvements included the expansion of the heat transfer area, improved power transfer and brakes, an automated smoke box door, and other improvements. The Tehoro class was designed for use on both passenger and freight trains, and was used primarily on the Gyeongui and Gyeongbu lines.[1] The next thirteen came in 1929, five from Gyeongseong and four each from Mitsubishi and Hitachi's Kasato works;[1][4] the last of these became the largest producer of Tehoro class locomotives.[1] Another eighteen were delivered in 1937, nine each from Hitachi Kasato and Kawasaki,[1] and in 1938, as part of Sentetsu's general renumbering, the Tehoro class locomotives in service received numbers テホロ1 through テホロ39.[4] Finally, between 1939 and 1941, 56 more were delivered, mostly from Hitachi Kasato.[1]

The Tehoro class was a notable milestone in the history of Korea's railways. As the first type designed and produced entirely by domestic (Korean and Japanese) factories, it gave Japanese and Korean designers extensive experience which was subsequently applied to the development of the Pashishi and Mikasa-class locomotives.[1]