In this book the authors have endeavoured to remedy a notable lack of comprehensive coverage on this specialist subject. The development of all the many engines produced by Japanese aero-engine manufacturing companies from 1912 to 1945 is explored in detail, including a full explanation of the different systems used to identify them. Furthermore, the developments are related to the aircraft in which the various engines were used, including prototypes, flying test-beds, and changes in the make or type of engine during an aircraft's operational service. Aircraft evolution in Japan is viewed in snapshots as it happened from the aero-engine aspect and not from the complete aircraft aspect as is featured in most publications. Also, in order to illustrate the industrial background, the origin and development of each of the aero-engine manufacturing companies is also outlined briefly.