It may be useful to recapitulate the systems now used by the Japanese in
a. According to mythology, the Japanese Empire was founded in the year 660 B.C., and
it is from this date that Japanese years are calculated in one system of writing
dates. For example, our 1940 is the Japanese 2600, and so on. Type numbers for
Japanese aircraft and various other military equipment are often derived from
this system of dates. The last two digits of the year concerned, until
and including 2599 (1939), are used for the type number; from 2600 (1940) onward, the
last digit alone is used. Type "97" was adopted in the year 2597 (1937),
Type "0" (zero) in 2600 (1940), Type "1" in 2601 (1941), and so on.*
b. In more general usage, however, is the practice (in use since 1868) of
numbering years from the start of each Emperor's reign. A name is chosen for
each reign, and a given year is referred to by the number of years that have
elapsed since the reign started. The name of the reign of the present
Emperor, which began in 1926, is Showa (Enlightened Peace); 1943 is
thus the 18th year of Showa, or more simply "Showa 18."
c. The Western or Christian calendar is also in common use among the Japanese.
*For the use of the term "Zero" as applied to aircraft, see
Tactical and Technical Trends, No. 19, p. 1.