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 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. 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 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. ==Variants==