Richard Frank

“The complex Japanese aircraft designation systems proved confusing during and after the war. Several forms of nomenclature applied to Imperial Navy aircraft, but just two are important. The first system (“short form”) comprised a letter, number, letter (e.g., A5M). The first letter identified mission (A = carrier fighter, B = carrier bomber, G = land-based bomber, etc.). This was followed by a numeral indicating the numerical sequence of that model for the mission (5 = fifth carrier fighter). The second letter designated the manufacturer (the most important were A = Aichi, K = Kawanishi, M = Mitsubishi, N = Nakajima). The second major system was the type number from the year of service introduction under the Japanese calendar. By the Japanese calendar, 1936 was Year 2596, from which “96” was taken as the year of introduction. The year 1940 was Year 2600, hence the famous designation of the Mitsubishi A6M Carrier Fighter as the Type “0” or “Zero.” Imperial Army aircraft bore a Kitai (airframe) number (e.g., Ki-27), a type number/mission designator based on the Japanese calendar (Army Type 97 fighter had a 1937 year of introduction), and sometimes a name. The Imperial Navy resisted the use of names before capitulating to this system in 1943. To unify and simplify the identification of Japanese aircraft, the United States adopted a system by 1943 of providing male (fighters) and female (bombers) names for Japanese aircraft. Hence, the A6M “Zero” became officially the “Zeke” (although the Zero alone of Japanese aircraft continued to be widely known by that designation), while the “Nell” stood for the G3M and “Betty” for the G4M. This system has become so entrenched in decades of literature about the Pacific War that it will be used here for purposes of clarity.”
― Richard Frank, Tower of Skulls: A History of the Asia-Pacific War, Volume I: July 1937-May 1942