Japanese aircraft engine identification systems

Japanese aero-engines for military aircraft were given a wide variety of designations depending on the customer. This led to much confusion, particularly among the Allied forces, where a single engine type could have up to six different designations. This situation emerged because of the almost total lack of co-operation in weapons procurement between the IJAAS (大日本帝國陸軍航空隊 - Dai-Nippon Teikoku Rikugun Kokutai - Imperial Japanese Army Air Service) and the IJNAS (大日本帝國海軍航空隊 - Dai-Nippon Teikoku Kaigun Koukuu-tai - Imperial Japanese Navy Air Service).

Engines could have designations in any or all of these designation systems:

Army Hatsudoki experimental designation

(Kawasaki Ha40)

Army long designation

(e.g. Army Type 99 900hp Air Cooled Radial)

Navy experimental designation

(Nakajima NK9B)

Navy Name designation

( Nakajima Homare 11)

Manufacturers designation

(Nakajima NBA)

Unified system introduced by the Ministry of Munitions in April 1942

(Kawasaki Ha-60)

Data from:Japanese Aircraft 1910–1941 & Japanese Aircraft of the Pacific War & Japanese Aircraft Engines