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

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 Type 100 1,450hp Air Cooled Radial – (Nakajima Ha111) The two or three digit Type number denoted the 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

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 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.

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 – (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: 130/160 140/130 150/170 140/150 140/160 130/150

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 (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 yearType number (Army and Navy)Imperial Japanese Calendar YearNengo Calendrical eraNavy exp.Shisaku number1921Type 10 (Taisho)2581Taisho 101922Type 11 (Taisho) 2582 Taisho 11 1923 Type 12 (Taisho)2583Taisho 121924 Type 13 (Taisho)2584Taisho 131925 Type 14 (Taisho)2585Taisho 1425/12/1926 Type 15 (Taisho)25/12/2586Taisho 1526/12/1926 26/12/2586Showa 11927 Type 872587Showa 21928 Type 882588Showa 31929 Type 892589Showa 41930 Type 902590Showa 51931 Type 912591Showa 66-Shi1932 Type 922592Showa 77-Shi1933 Type 932593Showa 88-Shi1934 Type 942594Showa 99-Shi1935 Type 952595Showa 1010-Shi1936 Type 962596Showa 1111-Shi1937 Type 972597Showa 1212-Shi1938 Type 982598Showa 1313-Shi1939 Type 992599Showa 1414-Shi1940 Type 100 / Type 02600Showa 1515-Shi1941 Type 12601Showa 1616-Shi1942 Type 22602Showa 1717-Shi1943 Type 32603Showa 1818-Shi1944 Type 42604Showa 1919-Shi1945 Type 52605Showa 2020-Shi

Table of japanese aero-engine designations Manufacturer Army exp. Army long Navy exp. Navy Name Manuf desig. UnifiedNotes NakajimaHa1Army Type 97 650hp Air-cooled Radial AH NakajimaNZ 7-cylinder radial MitsubishiHa2Army Type 93 700hp Water Cooled In-line NakajimaHa5Army Type 97 825hp Air Cooled Radial MitsubishiHa6MK1A6(7)14 cyl. radial NakajimaHa8Army Type 94 550hp Air Cooled Radial KawasakiHa9Army Type 98 850hp Liquid Cooled In-lineliquid-cooled V-12 (BMW VI) HitachiHa12Army Type 95 150hp Air Cooled Radial HitachiHa13Army Type 95 350hp Air Cooled Radial HitachiHa13aArmy Type 98 450hp Air Cooled Radial NakajimaHa20 Lorraine-DietrichLorraine 1IJN designation for imported Lorraine-Dietrich 12D V-12 engines Lorraine-DietrichLorraine 2IJN designation for imported Lorraine-Dietrich 12Eb W-12 engines Lorraine-DietrichLorraine 3IJN designation for imported geared Lorraine-Dietrich 12Eb W-12 engines NakajimaHa25Army Type 99 975hp Air Cooled Radial / Army Type 99 950hp Air Cooled Radial NK1Ha-35 MitsubishiHa26Army Type 99 900hp Air Cooled RadialMK2A14Ha-31 HitachiHa38600 hp 9-cyl radial NakajimaHa39 KawasakiHa40Army Type 2 1,100hp Liquid Cooled In-lineHa-60liquid-cooled V-12 NakajimaHa41Army Type 100 1,250hp Air Cooled Radial HitachiHa429-cyl radial NakajimaHa45 Army Type 4 1,900 hp Air-cooled RadialNK9NBAHa-45 HitachiHa47Army Type 4 110hp Air Cooled InlineGK4 NakajimaHa5122cyl HomareHa-51Air-Cooled 22-Cylinder 2-Row Radial Yokosuka Naval Air ArsenalHa73Ken No. 3YE2W-18 Yokosuka Naval Air ArsenalHa74YE3 (Ken No. 1)2,500 (or 3,200) shp horizontal X-24 liquid-cooled engine, known as

Yokosuka Naval Air Arsenal YE3B (Ha 74 Model 01) or YE3E (Ha 74 Model 11) MitsubishiHa101Army Type 100 1,450hp Air Cooled RadialMK4A10Ha-32 MitsubishiHa102Army Type 100 1,050hp Air Cooled RadialMK2A14Ha-31 NakajimaHa103NK7NAKHa-36 MitsubishiHa104Army Type 4 1,900hp Air Cooled Radial NakajimaHa105 NakajimaHa109Army Type 2 1,450hp Air Cooled RadialHa-34 MitsubishiHa111Army Type 100 1,450hp Air Cooled RadialMK4A10Ha-32 MitsubishiHa112Army Type 4 1,500hp Air Cooled RadialMK8A8Ha-33 NakajimaHa115Army Type 1 1,150 Air Cooled Radial NakajimaHa117 KawasakiHa140liquid-cooled V-12 NakajimaHa145 KawasakiHa201Ha-72liquid-cooled inverted V-24 MitsubishiHa211MK9Ha-43 MitsubishiHa214 NakajimaHa217Ha-46 NakajimaHa219Ha-43 NakajimaHa315 NakajimaHa50536 cyl KotobukiHa-54-01projected 5,000 hp Air-Cooled 36-Cylinder 4-Row Radial AichiAichi AE1Aichi Atsuta AichiAichi Type 91W-12 water-cooled AichiHa-70Coupled Atsuta 30 engines HiroHiro Type 14 620 hp HiroHiro Type 90 600 hp water-cooled W-12500 hp W-12 (Lorraine 12F Courlis development) HiroHiro Type 91 520 hp water-cooled W-12500 hp W-12 (Lorraine 12Eb development) HiroType 94 900 hp liquid-cooled in-line40 degree angle W-18 Hitachi / Gasuden Hitachi / Gasuden160 hp 7-cyl. radial Hitachi GK2 / HitachiHa-234-cyl inverted in-line Ishikawajima Shibauru Turbine Company / Yokosuka (Kugisho)Ishikawajima Ne-20 ()turbojet Ishikawajima Shibauru Turbine CompanyNe-30turbojet Ishikawajima Shibauru Turbine CompanyNe-130turbojet KawasakiArmy Type 95 800hp Liquid Cooled In-lineliquid-cooled V-12 (BMW VI) Maru IndustriesMaru Ka-10pulse-jet MitsubishiA2320 hp MitsubishiA4760 hp MitsubishiA9 MitsubishiArmy Type 92 400hp Air Cooled RadialA5 MitsubishiMK10 MitsubishiNe-330turbojet NakajimaNK11 MitsubishiMitsubishi Tokuro-1 Ro.1 MitsubishiArmy Type3 RocketKR10Mitsubishi Tokuro-2 Ro.2Walter HWK 109-509 MitsubishiArmy Type 2 Rocket Mitsubishi Tokuro-3 Ro.3 Ne-12turbojet Nakajima - HitachiNe-230turbojet Tsu-11Thermojet Navy Type 4 Model 1 solid fuel rocket KobeArgus As 10 Ka-10Argus As 109-014Pulsejet

See also 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

References

Bibliography

External links Japanese Military Aircraft Designations (after 1945)