The Mitsubishi Shinten was a development of the Mitsubishi Kinsei engine. The stroke of the Kinsei was increased from to on the Shinten model 11 and to on the Shinten model 21 and 21Kai designs. Lengthening the stroke increased the displacement from the Kinsei's to for the Shintin model 11. The increased displacement raised the horsepower from to at take-off power. Initially Ha-6 Shintens were to be installed on Mitsubishi Ki-21bomber aircraft, but it was decided to use a competing engine, the Nakajima Ha-5 instead. Furthermore, Mitsubishi was ordered to produce Nakajima's engine at its factory under license. So only 113 Shinten engines were made and they were installed on only few types of aircraft. In order to beat the rival and also to develop a more powerful engine for the new Navy Attack Bomber that became famous Mitsubishi G6M Betty, Mitsubishi Shinten was developed into the Mitsubishi Kasei by increasing the bore from to which in turn brought the displacement to and increased power to.
It was the Imperial Japanese Navy's common practice to refer to its engines by name. The Japanese method of identifying model numbers of aircraft engines is unique in that the model number always has two digits and may be followed by one or more letters. The first digit represents the major version of the engine and the second number represents the minor version of that model engine. The first model number assigned to an engine is always 11, meaning the first major design and first minor version of that design. A major change to the design increments the first number and resets the second number to one. A minor change to the engine model increments the second number by one. If a very minor change is made, suffix letters are added after the model number. When a special modification is made, the model number is followed by the suffix 'kai', as in the Shinten 21kai model, which decodes as the second model of the Shinten engine, 1st revision, specially modified.
IJAAS engine naming method
The Imperial Japanese Army Air Service referred to its engines by their engine model number. Ha numbers were assigned in sequence as the engine design was accepted. This engine would be the 6th engine accepted by the IJAAS.
