When in 1938 the Mitsubishi Ki-21 heavy bomber began to enter service with the Imperial Japanese Army, its capability attracted the attention of Japan Air Lines. In consequence a civil version was developed and this, generally similar to the Ki-21-I and retaining its powerplant of two 950 hp (708 kW) 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 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.

A Mitsubishi Ki-57-II "Topsy" of the Imperial Japanese Army during 1943

This initial production Mitsubishi 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 L4Ml. After the last of the Ki-51s had been delivered production was switched to an improved Ki-57-II, which introduced more powerful 1,080 hp (805 kW) 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, and 406 were built before production ended in January 1945. Both versions were covered by the Allied codename 'Topsy'.

Variants

Ki-57-I Army Type 100 Transport Model 1 - Powered by two 950 hp (708 kW) Nakajima Ha-5 KAI radial engines and a redesigned fuselage to accommodate 11 passengers. About 100 aircraft of this type were built including the civil version.

MC-20-I - Same as above but built for civil use with Japan Air Lines (Dai Nippon Koku KK).

Ki-57-II Army Type 100 Transport Model 2 - Powered by two 1,080 hp (805 kW) Mitsubishi Ha-l02 14-cylinder radial engines installed in redesigned nacelles. Minor equipment and detail refinements were also incorporated. 306 aircraft of this type were produced before the end of production in January 1945.

MC-20-II - Same as above but built for civil use with Japan Air Lines (Dai Nippon Koku KK).

L4M1 - A small number of Ki-57-IIs were transferred for use by the Japanese navy as transports and were redesignated L4M1.

(Army Type 100 Transport Model 2 - Mitsubishi Ki-57-II)

Allied Codename: Topsy

Type: 11 Passenger Personnel Transport

Accommodation/Crew: Pilot, Co-Pilot, Navigator and Radio Operator.

Design: Mitsubishi Jukogyo KK Design Team to create a civil version of the Ki-21 bomber initially for Japan Air Lines (Dai Nippon Koku KK)

Manufacturer: Mitsubishi Jukogyo Kabushiki Kaisha (Mitsubishi Heavy Industries Limited)

Powerplant: (Ki-57-I) Two 950 hp (708 kW) Nakajima Ha-5 KAI radial engines. (Ki-57-II) Two 1,080 hp (805 kW) Mitsubishi Ha-102 14-cylinder air-cooled radial engines.

Performance: Maximum speed 292 mph (470 km/h) at 19,030 ft (5800 m); service ceiling 26,245 ft (8000 m).
Range: 1,864 miles (3000 km) on internal fuel.

Weight: Empty 12,313 lbs (5585 kg) with a maximum take-off weight of 20,106 lbs (9120 kg).

Dimensions: Span 74 ft 1 3/4 in (22.60 m); length 52 ft 9 3/4 in (16.10 m); height 15 ft 11 in (4.85 m); wing area 754.36 sq ft
(70.08 sq m).

Armament: None.

Variants: Mitsubishi Ki-57 (prototype), MC-20-1 (civil production), Ki-57-I Army Type 100 Transport Model 1 (military production), MC-20-II (civil production), Ki-57-II Army Type 100 Transport Model 2 (military production), L4M1 (naval).

Equipment/Avionics: Standard communications and navigation equipment.

History: First flight (prototype) August 1940; service introduction (Ki-57-II) early 1942.