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 and the IJNAS .
Engines could have designations in any or all of these designation systems:
;Army Hatsudoki experimental designation:
;Army long designation:
;Navy experimental designation:
;Navy Name designation:
;Manufacturers designation:
;Unified system introduced by the Ministry of Munitions in April 1942:
Data from:Japanese Aircraft 1910–1941 & Japanese Aircraft of the Pacific War & Japanese Aircraft Engines

Army Hatsudoki system

Experimental engines for Army aircraft were given ハ Ha – 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 [Type 100 1,450hp Air Cooled Radial] –
The two or three digit Type number denoted the Japanese Imperial year that the engine was introduced, identical to the Type numbers used in Japanese aircraft long designations from 1925 :
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

Navy experimental designation

The IJNAS introduced a designation system for experimental engines and those under development / test before production. Once the engine entered 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
;Second Character for engine attributes
;Third Character for the design number
;Fourth Character for the revision code
;B - second revision, and so on.

Navy name designation

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 -

Manufacturers designation

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 – 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 - 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:
  1. Air-cooled inline engine.
  2. Air-cooled single-row radial engine.
  3. Air-cooled 14-cylinder double-row radial engine.
  4. Air-cooled 18-cylinder double-row radial engine.
  5. Air-cooled, more than 18-cylinders, multi-row radial engine.
  6. Liquid-cooled 12-cylinder engine.
  7. Liquid-cooled, more than 12-cylinders engine.
  8. Diesel engine.
  9. Special engine.
The second digit represented the bore and stroke of the engine:
  1. 130/160
  2. 140/130
  3. 150/170
  4. 140/150
  5. 140/160
  6. 130/150
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
  • 10
  • 20
  • 30
  • 40
  • 50
  • 60
etc.etc.
A revision state number replaced the second digit of the model number:
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 yearType number Imperial Japanese Calendar YearNengo Calendrical eraNavy exp.Shisaku number
1921Type 10 2581Taisho 10
1922Type 11 2582Taisho 11
1923Type 12 2583Taisho 12
1924Type 13 2584Taisho 13
1925Type 14 2585Taisho 14
25/12/1926Type 15 25/12/2586Taisho 15
26/12/192626/12/2586Showa 1
1927Type 872587Showa 2
1928Type 882588Showa 3
1929Type 892589Showa 4
1930Type 902590Showa 5
1931Type 912591Showa 66-Shi
1932Type 922592Showa 77-Shi
1933Type 932593Showa 88-Shi
1934Type 942594Showa 99-Shi
1935Type 952595Showa 1010-Shi
1936Type 962596Showa 1111-Shi
1937Type 972597Showa 1212-Shi
1938Type 982598Showa 1313-Shi
1939Type 992599Showa 1414-Shi
1940Type 100 / Type 02600Showa 1515-Shi
1941Type 12601Showa 1616-Shi
1942Type 22602Showa 1717-Shi
1943Type 32603Showa 1818-Shi
1944Type 42604Showa 1919-Shi
1945Type 52605Showa 2020-Shi