Japanese Aircraft Designations 1939-1945
by Randy Wilson
This document was originally written as an informal guide for AAHM docents. It has not been otherwise published in print, as of this date.
Like the U.S., Japan's Army and Navy each had their own systems of aircraft designation, in some cases as many as four or five systems! Because of this confusion, the Allied forces started assigning code names to each Japanese type, and it is these code names that are most often remembered now.
We will begin by looking at the Imperial Japanese Navy's (IJN) designation systems, as our (Confederate Air Force) Zero and Tora aircraft are all IJN aircraft or replicas.
Japanese Navy Aircraft Designations
At the beginning of World War II, the Japanese Navy Air Force (JNAF) used three different systems to designate their aircraft: one, the Shi number; two, a type number system and three, a type/model/manufacturer code (called the short designation). Later during the war, two new systems were added, popular names and the Service Airplane Development Program (SADP) system.
Experimental Shi Numbers
Every new design, real or projected, from 1931 onward received an experimental or Shi number derived from the current year of the Japanese imperial reign, which for emperor Hirohito began in 1926 and was called Showa. Added to the Shi number was the purpose of the new design, (i.e. carrier fighter, carrier bomber, etc.) to differentiate between different designs. Thus, the Zero was designed to meet a 1937 specification called the 12-shi carrier fighter, that year being the twelfth year of Showa.
Type and Model Number System
Each type of aircraft entering production for the JNAF after 1920 was given a type number combined with a brief description of its primary function. Initially related to Showa dates, in 1929 the type number became the last two digits of the year in the Japanese calendar year. Thus the Aichi dive-bomber which entered production in 1939 (2599 in the Japanese system) was the Type 99 Carrier Bomber. Only a single digit was used when the year ended in 00, as with the Type 0 Carrier Fighter (thus the name "Zero") which entered production in 1940 or the Japanese year 2600.
Subtypes and new versions of a type were indicated by model numbers added after the type. By the late 1930s, model numbers had evolved to two digits beginning with 11 for the first version, indicating the first airframe version and the first powerplant configuration. Thus the Type 0 Carrier Fighter Model 11 was the original production Zero, while the Model 21 was the next production version, with the addition of folding wing tips (thus the "2" for airframe modification in 21). The Type 0 Carrier Fighter Model 52 was the Zero after 5 major airframe and 2 engine configurations.
Further modifications to model numbers were indicated by the Japanese characters Ko, Otsu, Hei, etc. which are normally displayed as lower case Roman letters "a", "b", "c", etc. (i.e. Navy Type 0 Carrier Fighter Model 52c).
Short Designation by Type and Manufacturer
In the late 1920s, the IJN designed an aircraft designation system remarkably similar to that used by the U.S. Navy from 1922 until 1962. Each new design was given a "short designation" consisting of a group of Roman letters and numbers. The first letter (sometimes two) indicated the basic type or purpose of the aircraft, as indicated in the following table:
Following the type came a series number indicating the number of major sub-types produced by that manufacturer. Unlike USN practice, the digit "1" was not ignored in this system and was included. Thus the designation G4M designated the fourth attack bomber (G4) designed or produced by Mitsubishi (M, see below).
The second letter was, as indicated above, the manufacturer's code, and included some non-Japanese companies, as shown in the table below:
The first two letters and the series number remained the same for the service life of each design, however, minor to moderate changes in the design (usually reflected in a new Type Model number) were indicated by adding a second subtype number after the manufacturer's letter. Further minor changes were indicated by adding letters after the subtype number as in the Type/Model scheme above.
In a few cases, when the designed role of an aircraft changed, the new use was indicated by adding a dash and a second type letter to the end of the existing short designation. Thus the H6K4 was the sixth flying boat (H6) designed by Kawanishi (K), fourth version of that design (4). When the plane was equipped primarily as a troop or supply transport, its designation was then H6K4-L.
In July 1943, official names were given to JNAF aircraft in place of type numbers. These names were chosen based on the aircraft's primary role as listed below:
These popular names were most used on designs which came into service later in the war, such as the Mitsubishi J2M Raiden (Thunderbolt) and Kawanishi N1K Shiden (Violet Lightning), both interceptors.
The Service Airplane Development Program was begun in 1939 as a research program by the IJN's Bureau of Aeronautics. Each design studied was to be coded with its manufacturer's letter under the existing short designation system, plus a two digit number (i.e. 10, 20, 30, etc.). However this system was not widespread, and few records of SADP designations survived the war.
Japanese Army Aircraft Designations
The Japanese Army Air Force used two aircraft designation systems, the type number system and the Kitai number system. In addition, some types had a popular name.
From 1927, new Army aircraft were given a type number based on the last digits of the Japanese year that the type was accepted into service. Up to the year 2599 (1939 in the West) the last two digits formed the type number. In 2600 (1940) the number 100 was used, and from 2601 (1941) only the last digit of the year was used.
Thus, the Army Type 97 Heavy Bomber and Army Type 97 Fighter were both accepted in 2597 (1937) and can be differentiated by the functional description attached to each.
New versions of an existing type were indicated by adding a Model number and letter, i.e. Army Type 3 Fighter Model 2A.
The type number system required rather lengthy descriptive function names to fully identify an aircraft. The Kitai or Ki number system began in 1932 and assigned a number to each aircraft planned or projected to be built. Some existing aircraft also were given Ki numbers. At first the numbers were assigned sequentially but in 1944, new Ki numbers were scrambled, as if Allied intelligence wasn't confused enough!
New versions of an existing design had Roman numbers (I, II, III, etc.) added to the Ki number and subvariants had lower case letters (a, b, c, etc.) as used in some navy systems. And sometimes, the model and variant numbers and letters were supplanted by a Kaizo (KAI) or modification code! Let's look at the Kawasaki Hien, with a Kitai number of 61 and Allied code name TONY, as an example.
The project and prototypes were called Ki-61. The first two production versions were Ki-61-Ia and Ki-61-Ib. The next two versions carried KAI modification codes as Ki-61-I KAIc and KAId. Finally, the prototype of a second model was Ki-61-II and the first production of this new model was Ki-61-II KAIa. Whew!
Just to tie things up, the last example, the Ki-61-II KAIa was called the Army Type 3 Fighter Model 2A in the type number system. And a few foreign designed or built aircraft entered Japanese service, and these were given an alphabetical type rather than a numeric one, based on either the country of origin (Type I Heavy Bomber, for the Italian Fiat B.R. 20) or the manufacturer's name (Type LO Transport for the U.S. Lockheed Model 14).
Even the Japanese Army had problems using their lengthy aircraft designations in combat, and assigned popular names to many of the major combat types in service. Unlike the navy, however, the army chose names without any clear pattern.
Thus the Ki-61 fighter was Hien (Swallow), the Ki-43 fighter was Hayabusa (Peregrine Falcon) and the Ki-67 bomber was Hiryu (Flying Dragon).
The Allies Answer to Japanese Aircraft Designations
As you can imagine from the above discussion, even when one knows that the full designation of an aircraft is Aichi D3A1 Navy Type 99 Carrier Bomber Model 11, you might wish to have a short, simple and unmistakable name, especially when you are in combat with it!
In the second half of 1942, a colorful set of code names was developed in the Southwest Pacific Theater by the Air Technical Intelligence Unit (ATIU) of the Allied Air Forces in Australia. The head of the unit, Captain Frank T. McCoy Jr. was from Nashville, Tennessee, and the first few code names were hillbilly names such as ZEKE, NATE, PETE, JAKE and RUFE, as they were simple, short and distinctive. The basic system spread rapidly, and by late 1942, was adopted for use by both the USAAF and USN. In general, the code names were assigned using the following system, although several exceptions exist:
Thus, the example Aichi given above, became simply VAL in the Pacific code name system. As we learned more about the various models of each type, the Japanese model number was often attached to the code name, as in ZEKE 32 for the A6M3 Type 0 Carrier Fighter Model 32 "Zero".
Obviously, these code names were much easier to remember and say for Allied airmen and thus, even today, discussions of the Pacific war are filled with names such as BETTY, PETE, OSCAR, KATE and TONY.
List of Japanese Army and Navy Aircraft and their Code Names
Aircraft marked with a single asterisk(*) were fictional, and did not exist. Those with a double asterisk(**) were identified as more than one type, i.e. they are duplicated in the list. This list is extracted and edited from Mikesh's Japanese Aircraft Code Names & Designations.
Sources and Further Reading
An excellent single source on Japanese Army and Navy aircraft is Rene J. Francillon's Japanese Aircraft of the Pacific War, published by Putnam and others.
Another specific reference is Japanese Aircraft Code Names & Designations by Robert C. Mikesh, published by Schiffer. This book has some interesting history behind the development of the Allied code names, as well as a short discussion of each aircraft, including some rather minor types.
For a humorous and unfortunately typical American view of Japanese military and naval air power in early 1941, check out the article Japan Is NOT an Air Power.
All material not specifically credited is Copyright © by Randy Wilson.
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