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Why's a Zero?

During the 1930s and 1940s, an educated Japanese would be able to reckon dates by three different calendars. For discourse with foreigners, he would follow the western calendar, but for everyday use he'd prefer the Showa calendar, based on the year Hirohito became emperor. ("Showa" means Enlightened Peace, the name Hirohito took for himself and his reign when he succeeded his father in 1926.) And for military purposes, he'd follow the koki calendar, based on the mythical founding of the Japanese dynasty in 660 BC. Here's how the war years are shown in the three styles:

West  Showa  Koki       landmark event

1931      6      2591      Japanese army seizes Manchuria

1932      7      2592      Japanese navy raids Shanghai

1933      8      2593

1934      9      2594

1935      10    2595

1936      11    2596

1937      12    2597      invasion of China

1938      13    2598      Rape of Nanjing

1939      14    2599      border war with Russia

1940      15    2600      occupation of northern Vietnam

1941      16    2601      to war with U.S., Britain, Dutch

1942      17    2602      Battle of Midway

1943      18    2603

1944      19    2604      B-29s begin to destroy Japan

1945      20    2605      Japan surrenders

Why is this of interest? Mostly because, starting about 1936, the Japanese began identifying their military equipment by the last digits of its year of adoption, using the koki calendar. The numerical designation was followed by a description of its function. Thus, when the Pacific War began, these were the army and navy fighter planes in service:

Type 96 Carrier Fighter - Mitsubishi A5M, adopted 1936 (2596), with a few examples in secondary combat units in December 1941 ("Claude" in the Allied code-name system)

Type 97 Army Fighter - Nakajima Ki-27, adopted 1937 (2597), obsolete by December 1941 but still the army's basic fighter ("Nate")

Type 0 Carrier Fighter - Mitsubishi A6M, adopted 1940 (2600), a tremendous success in China that year; about 400 available in first-line squadrons when Japan went to war ("Zeke"; later "Zero")

Type 1 Army Fighter - Nakajima Ki-43, adopted 1941 (2601) but still experimental when the war began, with about 40 in two front-line groups (Hayabusa to its pilots, "Oscar" to Americans)

So "Zero" is merely the English translation of the Japanese character for a nul quantity, which was applied to the aircraft because it went into service in 2600. The Japanese called it Rei-sen, short for Rei (Zero) shiki (Type) sentoki (Fighter). Foreigners who like to parade their knowledge sometimes make a half-translation and call the plane "Zero-sen," but this is to conflate two languages. The correct usage is A6M, or Rei-sen—or Zero!