Japanese aircraft engine identification systems
|Japanese aircraft engine designation 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
- (Nakajima Ha41)
- Army long designation
- (e.g. Army Type100 1250hp Air Cooled Radial)
- Navy experimental designation
- (Nakajima NK9B)
- Navy Name designation
- ( Nakajima Homare 11)
- Manufacturers designation
- (Nakajima NBH)
- Unified system introduced by the Ministry of Munitions in April 1942
- (Kawasaki Ha-60)
- 1 Army Hatsudoki system
- 2 Army long designation system
- 3 Navy experimental designation
- 4 Navy name designation
- 5 Manufacturers designation
- 6 Unified IJAAS / IJNAS designation system
- 7 Calendars and Type numbers
- 8 Table of japanese aero-engine designations
- 9 See also
- 10 References
- 11 Bibliography
- 12 External links
Army Hatsudoki system
Experimental engines for Army aircraft were given ハ Ha – (エンジン - Hatsudoki) numbers whilst under design and testing. The Army Ha numbers had no intrinsic meaning and were only sequentially allocated. Sub types could be identified by suffixes -kai, -ko etc., or -I, -II etc.. e.g.:Nakajima Ha115
Army long designation system
Once an engine had been accepted for service in Army aircraft it was given a long designation which denoted the year of introduction, power, cooling method and layout:
e.g.:Army Type100 1250hp Air Cooled Radial – (Nakajima Ha41) The two or three digit Type number denoted the Japanese Imperial year (皇紀 kōki?) that the engine was introduced, identical to the Type numbers used in Japanese aircraft long designations from 1925 (From 1927 to 1930 the Type number sometimes denoted the Shōwa or Taisho year ):
After the Type number the power of the engine was denoted in horsepower:
- 1250 hp
After the power designator the type of engine was denoted:
- Air-cooled Radial
Sub-types were designated by suffixes.
- Model 1
The IJNAS introduced a designation system for experimental engines and those under development / test before production. Once the engine entrred service this designation was replaced by the name or unified system. Formed from four character groups the IJNAS experimental designation system consisted of e.g. Nakajima NK9B
- First character for manufacturer
- A - Aichi
- G - Hitachi
- I - Ishikawajima
- K - Kawasaki
- M - Mitsubishi
- N - Nakajima
- Y – Naval Air Technical Arsenal (Yokosuka and Hiro)
- Second Character for engine attributes
- K - Air cooled
- E - Liquid Cooled
- D - Diesel
- Third Character for the design number
- Fourth Character for the revision code
- A - first revision
- B - second revision, and so on.
The simplest of all the systems the IJNAS allocated name characters to engines combined with Model and revision numbers, introduced to reduce confusion and also to reduce the intelligence value of the designation to enemies. e.g. Nakajima Homare 11 - (praise" or, more usually, "honour (誉 Homare?))
Some engines were never allocated a designation or there is no record of such. In which case they are usually identified by the manufacturers designation. e.g. Mitsubishi A4
Unified IJAAS / IJNAS designation system
From 1942 the Ministry of Munitions in Japan instituted a Unified aero-engine designation system in an attempt to reduce confusion caused by previous systems. The new system prefixed engine designations with ハ Ha – (エンジン - Hatsudoki) followed by code numbers identifying each engine in terms of layout, no of cylinders, cooling method and sub-series model numbers.
Thus the Mitsubishi Ha-33-62 金星 Kinsei
- Mitsubishi - manufacturer
- ハ Ha (エンジン Hatsudoki) - engine.
- 3 - air-cooled 14-cylinder double-row radial engine.
- 3 - 140 mm bore, 150 mm stroke.
- 62 - 60 series engine, second revision.
- 金星 Kinsei - name
Each engine designation in this system started with the Hatsudoki short hand character, represented by Ha in English, followed by two numbers classifying the engine:
The first digit represented the engine classification:
- Air-cooled inline engine.
- Air-cooled single-row radial engine.
- Air-cooled 14-cylinder double-row radial engine.
- Air-cooled 18-cylinder double-row radial engine.
- Air-cooled, more than 18-cylinders, multi-row radial engine.
- Liquid-cooled 12-cylinder engine.
- Liquid-cooled, more than 12-cylinders engine.
- Diesel engine.
- Special engine.
The second digit represented the bore and stroke of the engine:
- 0. 130/160
After the classification digits a two digit number gave the model number and revision state.
Model numbers were given as:
- 00 – baseline Model, usually prototypes
A revision (or modification) state number replaced the second digit of the model number:
- 10 – Model 10 baseline version
- 11 – Model 10 revision 1
- 12 – Model 10 revision 2
- 23 – Model 20 revision 3
- 62 – Model 60 revision 2
Coincidentally one engine was assigned the same numerical designation in the IJAAS and joint designation systems; Nakajima Ha-45 Homare.
Calendars and Type numbers
Data from: 
|Gregorian calendar year||Type number (Army and Navy)||Imperial Japanese Calendar Year||Nengo Calendrical era||Navy exp.Shisaku number|
|1921||Type 10 (Taisho)||2581||Taisho 10|
|1922||Type 11 (Taisho)||2582||Taisho 11|
|1923||Type 12 (Taisho)||2583||Taisho 12|
|1924||Type 13 (Taisho)||2584||Taisho 13|
|1925||Type 14 (Taisho)||2585||Taisho 14|
|25/12/1926||Type 15 (Taisho)||25/12/2586||Taisho 15|
|1927||Type 87||2587||Showa 2|
|1928||Type 88||2588||Showa 3|
|1929||Type 89||2589||Showa 4|
|1930||Type 90||2590||Showa 5|
|1931||Type 91||2591||Showa 6||6-Shi|
|1932||Type 92||2592||Showa 7||7-Shi|
|1933||Type 93||2593||Showa 8||8-Shi|
|1934||Type 94||2594||Showa 9||9-Shi|
|1935||Type 95||2595||Showa 10||10-Shi|
|1936||Type 96||2596||Showa 11||11-Shi|
|1937||Type 97||2597||Showa 12||12-Shi|
|1938||Type 98||2598||Showa 13||13-Shi|
|1939||Type 99||2599||Showa 14||14-Shi|
|1940||Type 100 / Type 0||2600||Showa 15||15-Shi|
|1941||Type 1||2601||Showa 16||16-Shi|
|1942||Type 2||2602||Showa 17||17-Shi|
|1943||Type 3||2603||Showa 18||18-Shi|
|1944||Type 4||2604||Showa 19||19-Shi|
|1945||Type 5||2605||Showa 20||20-Shi|
Table of japanese aero-engine designations
- Japanese military aircraft designation systems
- British military aircraft designation systems
- List of RLM aircraft designations for the Third Reich
- Mark (designation)
- Type (designation)
- World War II Allied names for Japanese aircraft
- Mikesh, Robert; Shorzoe Abe (1990). Japanese Aircraft 1910–1941. london: Putnam. ISBN 978-0-85177-840-2.
- Francillon, Rene (1979). Japanese Aircraft of the Pacific War. London: Putnam & Company Limited. ISBN 0 370 30251 6.
- Mawhinney, Robert. Japanese Aircraft Engines. Washington D.C.: NASM.