Type Number System (from 1921)
Popular Names (from 1943)
Short Designation System (from late 1920s)
Experimental Shi numbers (from 1931)
Service Aeroplane Development Programme system (from 1939)
Allied Code Names
Short Designation Lists by Letter
The Japanese Navy used two main and two subsidiary aircraft designation systems during the Second World War, causing so much confusion on the Allied side that a fifth codename system was developed.
The earliest of the designation systems in use during the Second World War was the Type number system, which began in 1921. In this system each Naval aircraft was given a type number based on the year it entered service, followed by a short description of the aircraft’s purpose.
From 1921 to 1928 the year code was based on the regnal year of the current Japanese Emperor. In 1921-26 this was the Emperor Yoshihito, whose reign was known as the Taisho Era, and so aircraft from those years were Types Taisho 10 to Taisho 15. Emperor Hirohito took the throne in 1926, and aircraft accepted in 1927 and 1928 became Types Showa 2 and Showa 3.
After 1928 the Japanese Navy copied the Japanese Army in using the last digits of the calendar year. 1929 was 2589 in the Japanese calendar, and so aircraft from that year became Type 89s. Aircraft accepted in 1940 (2600) became the Type 0, and after that the last digit of the year was used.
Different models of the same aircraft were originally given a single digit model number, with dash numbers for subtypes (Model 1 for the first version, Model 1-1 for the first subtype).
This was changed in the last thirties to a system that used a two digit code. The first digit changed if the airframe was altered, the second digit if the engine was altered. The first version of an aircraft was thus the Model 11. If the engine changed it became the Model 12, if the airframe changed it became the Model 21 and if both changed it became the Model 22.
Finally sub-versions of a model were given a final letter, taken from a series of Japanese characters called the Ten Stems (or Celestial or Heavenly Stems), which makes up part of the Japanese Zodiac. The full sequence runs kou (or ko) otsu hei tei bo ki kou shin jin ki and was originally used during the Chinese Shang dynasty as part of a dating system. In English translations they are normally replaced by the abc (ko=a, otsu=b, hei=c)
The Type numbers were abandoned in 1943 in favour of popular names, apparently in an attempt to improve security. Names were allocated according to strict rules, which must have rather reduced their confusion value.
Named after/ names ending in
Carrier and seaplane fighters
Ending in wind (pu or fu)
Ending in den (lightning)
Ending in light (ko)
Stars (sei) or constellations (zan)
Seas and oceans
Trees, plants or flowers
The best known of the main systems is the Short Designation System, which resembled a more logical version of the system used by the US Navy. In the Japanese system each type of aircraft was given a basic three symbol code running Letter-Number-Letter. The first letter gives the type of aircraft (A for carrier fighter or B for carrier based torpedo bomber – see below for a fuller list).
The numbers were allocated in sequence to each aircraft of that type to enter service, regardless of manufacturer, so unlike in the US Navy system we can be certain that the Yokosuka B4Y was an earlier aircraft than the Nakajima B5N (the US Navy started the numerical sequence from 1 for each aircraft company, so one company’s F1 could be a much more modern aircraft than another’s F10).
The second letter is normally described as the manufacturers code (see list below), but is better though of as the designing company’s code. Unlike in the US Navy this code was not changed to reflect the company that had manufactured a particular aircraft, so all Zero fighters were A6Ms, regardless of where they were built (in the US Navy system identical aircraft could have different numbers and company codes – the F4U and FG were both versions of the Corsair fighter – the first produced by Chance Vought, the second by Goodyear).
On a limited number of occasions two aircraft from a batch of designs submitted to a particular specification were accepted, and so shared a number.
These first three symbols were followed by a second number, which specified the exact model of an aircraft – the A6M2 was thus the second major version of the Zero. This was sometimes followed by a third lower case letter, used to distinguish between minor versions of a particular model.
In this system the A6M2c would thus be the fourth sub-version of the second model of the Mitsubishi produced sixth generation Carrier based fighter.
Early in the development of most aircraft the model number used here and the first digit of model designation in the Type number system were the same, but there was no direct connection, as shown in the A6M7 Model 63 version of the Zero.
If an aircraft was given a new purpose, that letter was hyphenated at the end of the designation, as with the Nakajima A6M2-N, a float plane fighter (-N) version of the Zero.
The main flaw with the type number and short designation systems was that they normally only applied to aircraft that reached a reasonably advanced stage of the design process. In 1931 they were supplemented by a system of experimental numbers based on the Imperial regnal year. 1931 was the sixth year of the reign of the Emperor Hirohito, or the sixth year of the Showa era. Projected that began in 1931 were thus known as Experimental 6-Shi, distinguished from each other by the manufacturers name and a short description of its main purpose. The Aichi B7A1 Ryusei, which entered service as the Navy Carrier Attack Bomber Ryusei in 1944, thus began life in 1941 as the Aichi Navy Experimental 16-Shi Carrier Attack Bomber.
The Service Aeroplane Development Programme designations are the least well known of the Naval designation system because most details were destroyed just before the end of the war. The system was used early in the development of an aircraft, and consisted of the manufacturer code from the short designation system and a two digit number.
The famous Allied codenames were adopted during 1942 in an attempt to end the confusion caused by a tendency to describe all Japanese fighters as Zeros and bombers as Mitsubishis. Very little was known about the Japanese aircraft industry before the start of the fighting, and many of the aircraft types were unfamiliar. The code name system was developed by Captain Frank T. McCoy Jr, of Nashville Tennessee, who in the summer of 1942 was appointed head of the Materiel Section, Directorate of Intelligence, Allied Air Forces, Southwest Pacific Area, Melbourne (Australia). Existing aircraft were allocated code names during 1942, and new aircraft were added to the list when they were identified. A number of codes were allocated to obsolete or non-existence aircraft, and one was allocated to the Messerschmitt Bf 109, which was widely expected to appear in the Pacific.
The Allied codenames were allocated according to a simple pattern – male first names for fighters and reconnaissance seaplane, tree names for trainers, bird names for gliders and female first names for bombers, flying boats, reconnaissance aircraft and transports.
Aichi or North American
Hitachi or Grumman
Hiro or Hawker
Nihon or Junkers
Kawanishi or Kinner
Watanabe then Kyushu
Mitsubishi A5M ‘Claude’
Mitsubishi A6M Reisen (Zero) ‘Zeke’ or ‘Zero’
Mitsubishi A7M Reppu (Hurricane) ‘Sam’
Yokosuka B3Y Navy Type 92 Carrier Attack Aircraft
Mitsubishi B4M1 Experimental 9-Shi Carrier Attack Aircraft
Nakajima B4N Experimental 9-Shi Carrier Attack Aircraft
Yokosuka B4Y Type 96 Carrier Attack Bomber Jean (or Kusho B4Y)
Nakajima B5N prototype 1936-37 accepted 1937 ('Kate')
Mitsubishi B5M1 ('Kate')
Nakajima B6N Tenzan (Heavenly Mountain) trials 1941
Aichi B7A Ryusei (Shooting Star) ‘Grace’ prototype 1942 produced 1944
Nakajima-Fokker C2N Reconnaissance Aircraft
Nakajima C3N Navy Type 97 Carrier Reconnaissance Aircraft
Nakajima C6N Saiun (Painted Cloud) ('Myrt')
Nakajima J1N-C Gekko (Moonlight)
Aichi D3A ‘Val’
Nakajima D3N Experimental 11-Shi Carrier Bomber
Yokosuka D3Y Myojo (Venus)
Yokosuka D4Y Suisei (Comet) ‘Judy’
Yokosho E1Y Type 14 Reconnaissance Seaplane
Nakajima E2N Type 15 Reconnaissance Seaplane
Aichi E3A1 Navy Type 90-1 Reconnaissance Seaplane (HD 56)
Nakajima E4N Type 90-2 Reconnaissance Seaplane
Yokosho E5Y Navy Type 90-3 Reconnaissance Seaplane
Yokosho E6Y Type 91 Reconnaissance Seaplane
Kawanishi E7K 'Alf'
Kawanishi E8K1 Experimental 8-Shi Reconnaissance Seaplane
Nakajima E8N Navy Type 95 Reconnaissance Seaplane 'Dave'
Watanabe E9W1 Navy Type 96 Small Reconnaissance Seaplane
Kawanishi E10K1 Experimental 9-Shi Night Reconnaissance Seaplane
Aichi E12A (prototype only)
Nakajima E12N1 Experimental 12-Shi Two-seat Reconnaissance Seaplane
Aichi E13A ‘Jake’
Kawanishi E13K1 Experimental 12-Shi Three-seat Reconnaissance Seaplane
Yokosuka E14Y ‘Glen’
Kawanishi E15K Shiun (Violet Cloud)
Aichi E16A Zuiun (Auspicious Cloud) ‘Paul’
Mitsubishi F1M ‘Pete’
Mitsubishi G3M ‘Nell’
Mitsubishi G4M ‘Betty’
Nakajima G5N Shinzan (Mountain Recess)
Nakajima G8N Renzen (Mountain Range) ‘Rita’
Nakajima G10N1 Fugaku (Mount Fuji)
Experimental Kusho 12-Shi Special Flying-boat H7Y1
Kawanishi H6K ‘Mavis’
Kawanishi H8K ‘Emily’
Aichi H9A Flying-boat trainer.
Yokosuka H5Y 'Cherry'
Nakajima J1N Gekko (Moonlight) ‘Irving’
Mitsubishi J2M Raiden (Thunderbolt) ‘Jack’
Mitsubishi J4M1 Senden (Flashing Lightning)
Nakajima J5N1 Tenrai (Heavenly Thunder)
Kawanishi J6K1 Jinpu (Squall)
Kyushu J7W Shinden (Magnificent Lightning)
Mitsubishi J8M Shusui (Swinging Sword)
Kawanishi N1K1-J Shiden (Violet Lightning) ‘George’
Yokosho K1Y Navy Type 13 Trainer
Yokosho K2Y Type 3 Land-based Primary Trainer
Mitsubishi K3M ‘Pine’
Yokosuka K4Y1 Type 90 Seaplane Trainer
Yokosuka K5Y ‘Willow’ Type 93 Intermediate Trainer
Kawanishi K6K1 Experimental 11-Shi Intermediate Seaplane Trainer
Watanabe K6W1 Experimental 11-Shi Intermediate Seaplane Trainer
Kawanishi K8K1 Navy Type 0 Primary Seaplane Trainer
Watanabe K8W1 Experimental 12-Shi Primary Seaplane Trainer
Kyushu K9W Momiji (Maple)
Kyushu K11W Shiragiku (White Chrysanthemum)
Aichi M6A1-K Nanzan (Southern Mountain)
Nakajima L1N1 Navy Type AT-2 Transport 'Thora'
Aichi M6A Seiran (Mountain Haze)
Kawanishi N1K Kyofu (Mighty Wind) ‘Rex’
Yokosuka P1Y Ginga (Milky Way) ‘Frances’
Kyushu Q1W Tokai (Eastern Sea) ‘Lorna’
Kyushu Q3W1 Nankai (South Sea) – never produced
Yokosuka R1Y Seiun (Blue Cloud)
Yokosuka R2Y Keiun (Beautiful Cloud)
Aichi S1A Denko (Bolt of Light)
Yokosuka P1Y-2 Kyokko (Aurora)
Yokosuka MXY7 Ohka (Cherry Blossom)
Kawanishi Baika (Plum Blossom)