Development
In 1938, when the Ki-21 heavy bomber began to enter service with the Imperial Japanese Army, its capability attracted the attention of the Imperial Japanese Airways. In consequence, a civil version was developed, and this, generally similar to the Ki-21-I and retaining its powerplant of two 708 kW (950 hp) Nakajima Ha-5 KAI radial engines, differed primarily by having the same wings transferred from a mid- to low-wing configuration and the incorporation of a new fuselage to provide accommodation for up to eleven passengers. This transport version appealed also to the navy, and, following the flight of a prototype in August 1940 and subsequent testing, the type was ordered into production for both civil and military use. [1]
This initial production Ki-57-I had the civil and military designations of MC-20-I and Army Type 100 Transport Model 1, respectively. A total of one-hundred production Ki-57-Is had been built by early 1942, and small numbers of them were transferred for use by the Japanese Navy in a transport role, then becoming redesignated L4M1. After the last of the Ki-57s had been delivered, production was switched to an improved Ki-57-II, which introduced more powerful 805 kW (1,080 hp) Mitsubishi Ha-102 14-cylinder radial engines installed in redesigned nacelles and, at the same time, incorporated a number of detail refinements and minor equipment changes. Civil and military designations of this version were the MC-20-II and Army Type 100 Transport Model 2, respectively. Only 406 were built before production ended in January 1945. Both versions were covered by the Allied reporting name Topsy. [2]
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