[3] Satisfied with the type, between 1924 and 1928 Mantetsu took delivery of 45 copies built by Kawasaki, Kisha Seizō, Nippon Sharyō, and Hitachi in Japan, as well as its own Shahekou Works in Dairen.

The Manchukuo National Railway was formed in 1933 and immediately placed an order for 34 of Mantetsu's Mikai class for use on the Duntu Line between Xinjing and Tumen.

The new type, called Mikako (ミカコ) class, featured a combustion chamber firebox and a feedwater heater, and eighteen locomotives, built by Kawasaki, Kisha Seizō, Hitachi, the Shahekou Works, and the Dalian Machine Works, were delivered between 1935 and 1937; these were numbered ミカコ1570−ミカイ1587.

Twenty units, ミカナ16718−ミカナ16736 and ミカナ16739, were built for the Manchukuo National but were diverted to the North China Transportation Company prior to delivery.

Of these, almost half - 527 - were built by Mantetsu's own Shahekou Works in Dairen, but the bulk of production, 617 units, was in Japan: 198 from Kisha Seizō, 167 from Kawasaki, 132 from Hitachi, and 95 from Nippon Sharyō.

[4] After the North Chosen Colonial Railway was nationalised in 1944, these locomotives were taken over by Sentetsu, but their subsequent numbering is unknown.

In 1950, the Sifang Works began assembling new Mikako type locomotives using parts that remained on hand after the war.

This included converting all dimensions from Imperial measures to metric, improving tolerances, and ensuring that everything met domestic materials standards.

[citation needed] The first locomotive built to the refined standards was ㄇㄎ壹2178, completed in December 1954 at the Dalian Works.

In 1957 engineers at the Dalian Works further improved the design, leading to the 建設 (JS) (Jiànshè, "Construction") class locomotives.

[6] Most were built at Sifang (216) and Dalian (187), with Qiqihar Works and other factories producing another 32, in addition to the one unit assembled by the crew of Taiyuan depot in 1958.

Additionally, China supplied more to North Korea as aid during the Korean War[1] - at least seventy of various JF classes, including JF1s.

An unknown number of the up to 54 Mikai class on loan to Sentetsu at the end of the war were in South Korea after the division, where they were put into service by the Korean National Railroad.

[2] A further twenty were built in Japan in 1952 (ten by Nippon Sharyō, five each by Hitachi and Kisha Seizō), but these were never delivered to South Korea.

[18][19] Due to the different standards in Japan and Korea (track gauge, axle load, clearance profiles), these were not taken up by the Japanese National Railways, and instead sat unused for many years until finally being scrapped, brand-new, in 1965.