Japanese calendars for time and 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:

http://www.danford.net/zero.htm

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.

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")

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, Rei-sen, or Zero.