The Japanese military aircraft designation systems for the Imperial period (pre-1945) had multiple designation systems for each armed service. This led to the Allies' use of code names during

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

, and these code names are still better known in English-language texts than the real Japanese names for the aircraft. A number of different schemes were simultaneously in use.

Imperial Japanese Navy Air Service

The used several different aircraft designation systems simultaneously. Between 1931 and 1945, aircraft had ''Shi'' numbers designating the specification they were designed to. They also had a long form of Type and Model Number system used between 1920 and 1943, a short designation system akin to that of the

United States Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

in use between the late 1920s and 1945, a system of popular names introduced to replace type numbers from 1943 through 1945.

Specification ''Shi'' numbers

Japanese Navy specifications from 1931 were given an experimental, or ''Shi'' (試) number, based on the year of the Emperor's reign the specification was issued in. Since multiple specifications could be issued in a year, the number was disambiguated with the aircraft purpose.Francillon 1970, pp.50–51. During the period this designation system was in use, the Emperor in question was

Hirohito Emperor , commonly known in English-speaking countries by his personal name , was the 124th emperor of Japan, ruling from 25 December 1926 until his death in 1989. Hirohito and his wife, Empress Kōjun, had two sons and five daughters; he was ...

, the ''Showa Emperor'', thus the years of ''Showa'' were those used, which began in 1926. Thus, the

Mitsubishi Zero The Mitsubishi A6M "Zero" is a long-range carrier-based aircraft, carrier-based fighter aircraft formerly manufactured by Mitsubishi Aircraft Company, a part of Mitsubishi Heavy Industries, and was operated by the Imperial Japanese Navy from 19 ...

was designed to meet the 1937 specification called ''12-shi carrier fighter''.

Long Type and Model Number system

After 1929, aircraft types were given a type number based on the last two digits of the

Japanese imperial year The , colloquially known as the or "national calendar year" is a unique calendar system in Japan. It is based on the legendary foundation of Japan by Emperor Jimmu in 660 BC. ''Kōki'' emphasizes the long history of Japan and the Imperial dyna ...

(which is counted from the mythical founding of Japan in 660BC by

Emperor Jimmu was the legendary first emperor of Japan according to the '' Nihon Shoki'' and '' Kojiki''. His ascension is traditionally dated as 660 BC.Kelly, Charles F"Kofun Culture"Mitsubishi Zero The Mitsubishi A6M "Zero" is a long-range carrier-based aircraft, carrier-based fighter aircraft formerly manufactured by Mitsubishi Aircraft Company, a part of Mitsubishi Heavy Industries, and was operated by the Imperial Japanese Navy from 19 ...

was so-called because entered service in 1940 which was the Japanese year 2600, thus it was designated ''Type 0 Carrier Fighter''. Model numbers were added to show subtypes. By the late 1930s these were two digits, the first being airframe revisions, the second engine revisions.Francillon 1970, pp.52–53. The system was abandoned in 1943, when it was decided that it gave away too much information about the aircraft.

Short system

In the late 1920s a short designation scheme was adopted, which was similar to the

1922 United States Navy aircraft designation system From 1922 until 1962, the United States Navy, the United States Marine Corps and the United States Coast Guard used a system to designate their aircraft that included information about a craft's role and its manufacturer. For a listing of all such ...

. This scheme used a letter or two letters to designate a type of aircraft, a number to indicate the Navy Design Request Number in that type of aircraft, and finally a letter to designate the manufacturer. Unlike the US Navy system, the Japanese system did not have a different number series for each manufacturer, and did not omit the number "1".Francillon 1970, p.51. Thus, the Zero's type in this designation system was A6M, which meant the sixth type of carrier fighter under this designation system, and that it was built by Mitsubishi. Variants were indicated by an additional number at the end; repurposing an aircraft was indicated by a dash and then the new type letter. Sometimes two aircraft were ordered from different manufacturers to the same specification at the same time, generally as insurance against the primary design not working out. In this case, the same series number was used for both. ''Data from:''Japanese Military Aircraft Designations

Official names

After July 1943, names were given to Navy aircraft instead of type designations. These names were given according to a scheme based on the aircraft's role. These were official names, in contrast to Army aircraft whose names were popular nicknames. * Fighters: Weather and meteorological names ** Carrier fighters and seaplane fighters: Wind names usually ending with ''pu'' or ''fu'' (風) ** Interceptors: Lightning names ending in ''den'' (電) ** Night fighters: Light names ending in ''ko'' (光) * Attack planes: Mountains names ending in ''zan'' (山) * Bombers: Star or constellation names usually ending in ''sei'' (星) * Patrol: Sea or ocean names ending in ''kai'' (海) or ''yo'' (洋) * Reconnaissance: Cloud names ending in ''un'' (雲) * Trainers: Trees, plants and flowers * Transports: Sky names ending in ''ku'' (空) * Miscellaneous: Landscape names * Purpose-built kamikaze aircraft: Flower names ending in ''ka'' (花) Special cases include aircraft that employed non-conventional (i.e. non-propeller-driven) propulsion scheme like rocket-powered interceptor Shūsui (poetic term meaning "Sharp Sword") and aircraft used for non-conventional deployments such as Special Attacker Seiran ("Mountain Haze"; deployed from submarines to strike targets behind the frontline and expected to be ditched upon returning to motherships).

Imperial Japanese Army Air Service

The (IJAAS) used a straightforward system based on year of service and type, nearly identical to the Navy's long type and model number system. This system was used from 1927, replacing an earlier system in which a manufacturer type code from a Japanese Kanji ordinal from the Heavenly stems was assigned to the aircraft from each company, as well as a type number. With additional types being added, this system quickly became cumbersome. Assigned letters included 甲 (Ko) for Nieuport, 乙 (Otsu) for Salmson, 丙 (Hei) for SPAD, 丁 (Tei) for Farman, 戊 (Bo) for Caudron, and 己 (Ki) for Hanriot. The "Ki" (キ; abbreviation of ''kitai'' = airframe) designation was also used and became prominent in later years.

Long Type and Model Number system

The first part of the designation was a two-digit type number based on the Japanese year in which the aircraft entered service. A minor exception was the year 1940 (2600), for which the type number 100 rather than zero was used. This was followed by a description of the aircraft's function.Francillon 1970, pp.48–49. If there were two or more aircraft with the same type and function, the latter was enhanced to further differentiate them. An example is the Type 2 single-seat fighter (the

Nakajima Ki-44 The Nakajima Ki-44 ''Shoki'' (鍾馗, " Devil Queller") was a single-seat fighter-interceptor which was developed by the Nakajima Aircraft Company and operated by the Imperial Japanese Army from 1942 to 1945 during World War II. Its official de ...

) and the Type 2 two-seat fighter (

Kawasaki Ki-45 The Kawasaki Ki-45 ''Toryu'' (屠龍, "Dragonslayer") was a two-seat, twin-engine heavy fighter used by the Imperial Japanese Army in World War II. The army gave it the designation "Type 2 Two-Seat Fighter"; the Allied reporting name was "Nick". ...

). Major modifications (such as a different engine) were indicated with a subtype number, officially in kanji but often in

Roman numerals Roman numerals are a numeral system that originated in ancient Rome and remained the usual way of writing numbers throughout Europe well into the Late Middle Ages. Numbers are written with combinations of letters from the Latin alphabet, eac ...

. Small-scale modifications (such as armament) are indicated with a Japanese Kanji ordinal from the Heavenly stems:- ko (甲), otsu (乙), hei (丙), tei (丁), bo (戊), ki (己), which equate to:- a (first), b (second), c (third), d (fourth), e (fifth), but are NOT direct translations. The character "kai"(改) was used if the modifications were large but not enough for a new type number.Francillon 1970, p.49.

Short designation ("Ki" number)

The "Ki" airframe designation indicates the project number (written in Arabic numerals), and was assigned in sequence to all projects regardless of manufacturer or type.Mikesh and Abe 1990, p.2.

Popular names

Popular names such as "Hayabusa" (the

Nakajima Ki-43 The Nakajima Ki-43 ''Hayabusa'' (, "Peregrine falcon", "Army Type 1 Fighter" ) is a single-engine land-based tactical fighter used by the Imperial Japanese Army Air Service in World War II. The Allied reporting name was "Oscar", but it was o ...

) were not part of the official designation.

Calendars and Type numbers

''Data from:'' Type numbers were assigned by both the Army and Navy followed the Taisho number sequence, the number of years the

Emperor Taisho An emperor (from la, imperator, via fro, empereor) is a monarch, and usually the sovereign ruler of an empire or another type of imperial realm. Empress, the female equivalent, may indicate an emperor's wife ( empress consort), mother ( e ...

had been on the throne until

Emperor Showa Emperor , commonly known in English-speaking countries by his personal name , was the 124th emperor of Japan, ruling from 25 December 1926 until his death in 1989. Hirohito and his wife, Empress Kōjun, had two sons and five daughters; he was ...

replaced him on 25 December 1926, which started the Showa sequence, at which time, the numbering was matched to the last two, or later one digit of the Imperial Japanese calendar year. The Navy began assigning Shisaku numbers to denote experimental types being evaluated by the Navy, whose numbering matched those of the Showa sequence. As no new designs were assigned Type numbers between 26 December 1926 and the end of the year, no aircraft was designated Type 86 under the Showa sequence. The Taisho/Showa sequences were used for almost all equipment developed for both Army and Navy (including weapons, equipment, vehicles and even ships), so there can be many unrelated pieces of equipment covered under a single Type number.

Designation table

This is a sortable table giving all the various designations and names of Japanese Military aircraft from circa 1925 to 1945. ''Data from:'' and .html" ;"title="ref name="zenibo Navy">">ref name="zenibo Navy">