The Mitsubishi Ki-57 was a Japanese passenger transport aircraft, developed from the Ki-21 bomber, during the early 1940s.
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 11 passengers.
This transport version appealed also 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 100 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-l02 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
Ki-57-I Army Type 100 Transport Model 1
Powered by two 708 kW (949 hp) Nakajima Ha5 KAI radial engines and a redesigned fuselage to accommodate 11 passengers.
MC-20-I
Same as above but built for civil use with Imperial Japanese Airways (Dai Nippon Koku KK).
Ki-57-II Army Type 100 Transport Model 2
Powered by two 805 kW (1,080 hp) Mitsubishi Ha-102 Zuisei 14-cylinder radial engines installed in redesigned nacelles.
Minor equipment and detail refinements were also incorporated.
MC-20-II
Same as above but built for civil use with Imperial Japanese Airways (Dai Nippon Koku KK).
L4M1
A small number of Ki-57-Is were transferred for test by the Japanese navy as transports and were redesignated L4M1.
