Kotobuki 1 KAI 1 radial aircraft engine was an aero-engine developed by Nakajima. It was a radial piston developed under licence from the Bristol Jupiter.
All of Japan's aircraft engines were imported or built under license until the mid-1930s, and the Japanese designs in production when war broke out in the Pacific were based on foreign designs. Almost all were air-cooled radial engines, and some were quite good. However, Japan was cut off from the remarkable advances in metallurgy made in the United States during the war years, and important alloying metals were in very short supply. Japanese engineers were too few in number and worked under a stifling military bureauracy. As a result, the performance of Japanese aircraft engines lagged badly behind those of her principal enemy as the war dragged on.