Japanese Heavy Bomber
The Ki-21 bomber, also known as the Sully during World War II, was developed by Mitsubishi designers in accordance with the requirements set by the General Aviation Directorate. The first prototype of the aircraft took off on December 18, 1936, and flight tests of prototypes took place over the next year. Serial production began in the spring of 1938. The bomber was produced by two factories, Nakajima and Mitsubishi, and the aircraft of these two different manufacturers had slight differences in the design of the nose of the fuselage. A modification of the aircraft designated Ki-21-Ib (the second production version of the Ki-21 bomber line) was produced with the experience of air combat in the skies of China and had enhanced small arms. The main visual difference between the bombers of this modification was the tail machine gun emplacement. The aircraft took an active part in combat operations during the Sino-Japanese War and the early stages of World War II. Subsequently, they were transferred to training units, and some of them were converted into transport aircraft.