In the late-1920s, as
Junkers developed the
Junkers G.38, Mitsubishi representatives in Germany expressed an interest in a military version of this civilian transport. At the time, the G.38 was the largest landplane in the world. Junkers completed a design study for a military bomber/transport, based on the G.38, designated the
K.51. This design was not accepted by the
Reichsluftfahrtministerium. The K.51 design study was of interest to Japan. A licensing and manufacturing agreement was reached and in 1932, the first two Ki-20s were completed by
Mitsubishi, utilizing Junkers-made parts. A prototype was successfully flown in Japan by a German test pilot in that year. Four additional Ki-20s were built between 1933 and 1935. All of these subsequent models used Mitsubishi-built parts. Ongoing development focused on engine upgrades to all examples to address the persistent issue of the aircraft being underpowered. Several engine upgrades were completed during the lifetime of these aircraft. The initial Junkers L88 engines were replaced by the more powerful
Jumo 204 engines, also built under license by Mitsubishi. Additionally, Kawasaki Ha-9 engines were utilized for testing purposes. ==Operational history==