皇紀 koki "imperial era"
National Era System
During the Meiji Restoration in 1868, the national era or imperial year calendar system was initiated, which counted years from the founding date of the imperial dynasty, 660 B.C. Type numbers for service aircraft were derived from the last one or two digits of the year; i.e., Type 96 Fighter indicates a fighter accepted for service in the year 2,596 (Gregorian 1936). This calendar system was used through the end of World War II.
大正時代 Taisho jidai "period of great righteousness"
Taisho Era System
In 1912, Yoshihito became emperor of Japan. He ruled from 30 July 1912 to 25 December 1926, which became known as the Taisho Era. The Taisho Era calendar system counts years starting from 1912. Aircraft accepted for service during this period received a Type designation using the Taisho Era year (see table below).
昭和時代 Showa jidai "period of enlightened peace"
Showa Era System
In 1926, Hirohito became emperor of Japan. He ruled from 25 December 1926 to 7 January 1989, which became known as the Showa era. The Showa Era calendar system counts years starting from 1926. Imperial Japanese Navy aircraft specifications used the Showa Era year (see table below).
The following table provides a calendar cross-reference for years starting from 1912 up to the World War II era, along with aircraft Type examples:
A portion of the Japanese zodiac (the "Ten Stems") was used by the Imperial Japanese Army and Navy to signify modifications to a basic design. These terms (ko, otsu, hei, tei, etc.) are sometimes translated into English as "a," "b," "c," "d," etc. However, this does not fully reflect the original Japanese context. This table illustrates the relationships of these terms within the Japanese zodiac:
IJA: Ki-61-I-Ko, Ki-61-I-Otsu, Ki-61-I-Hei, Ki-61-I-Tei are the designations of four sub-variants of the Kawasaki Ki-61-I Hien (Army Type 3 Fighter). These are sometimes translated as Ki-61-Ia, Ki-61-Ib, Ki-61-Ic, Ki-61-Id.
IJN: A6M3 Type 0 Carrier Fighter Model 32a; A6M5c Type 0 Carrier Fighter Model 52 Hei.
The Iroha is an ancient Japanese poem that contains each Japanese syllable exactly once and was often used as an ordering method.
Examples: Yokosho I-go Ko-gata Seaplane Trainer; IJN long-range submarines designated "I", coastal submarines designated "Ro" and training submarines
© 1997-2013, Robert Beechy
Originally posted 1998