The Mitsubishi A6M Zero fighter was one of the most famous fighter planes of the Second World War. But do you know what the “Zero” signifies? The Zero of the Mitsubishi Zero fighter represented the last two digits of Year 2600 in Kōki (皇紀) calendar – the year it was first commissioned – or 1940 in the Christian (Gregorian) calendar.

The Japanese have made use of several calendars throughout their history: namely the Gengō (元号), Kōki (皇紀), the Chinese Lunar and Christian calendars. The Gengō was perhaps the earliest used, with its origins traceable back to the Seventh Century. It basically records time according to the era of each Emperor. For example, Showa was the reigning years of Showa Tennō (The Emperor Hirohito), 25 December 1925 to 7 January 1989, in Gengō .

This system was imported from China and the Japanese started using it around 645 AD. The first Gengō was Taika (大化), 645 to 650 AD. After the Meiji Restoration in 1868, the meaning of Gengō changed to represent the era of each Emperor but, before that, Gengō did not necessarily mean the reigning year. Even in the middle of the reining year, the Emperor, or the ruler of the times, changed Gengō sometimes, especially after famines or spreads of disease to change people’s mood.

It was during the Meiji Restoration – around 1872 (The Meiji Fifth Year in Gengō) – where the Kōki and the Gregorian calendars were adopted for nation-building and modernisation purposes. For the latter, the Meiji government decided to introduce the Gregorian calendar (365 days a year, 7 days a week and 24 hours a day) on 15 December 1872.

However, at that point in time, Japan was still using the Chinese Lunar calendar; hence it was actually 15 November 1872 to the Japanese. So in implementing the change some two weeks later to coincide with the Western world’s turn of the New Year (1 January 1873), the Japanese effectively wiped out all but two days of December 1872 – i.e. 3 December 1872 in the Chinese Lunar calendar (also known as the Meiji Fifth Year) became 1 January 1873 (Meiji Sixth Year).

The Meiji Sixth Year was also known as Kōki 2533. At the same time, the Meiji Government introduced the Gregorian calendar, it also created the Kōki calendar after analysing details from the oldest Japanese history book – the Nihon-Shoki (日本書紀) (translated as the Chronicles of Japan). These books could be seen as the first Japanese history books. There are thirty volumes first published in 720 AD, compiling legendary histories (or mythology) inherited (or collected) by the Imperial Court.[1] The Nihon-Shoki is seen to depict the mythical beginnings of Japan – somewhat equivalent to Genesis in Western-Christian culture.

In the process of modern nation building, the Meiji Government merged this mythical story with new systems for rebuild Japan as a new Imperial State. It is easy to criticise this as a manifestation of Imperialism. But the Japanese monarchy is perhaps one of the few in existence where the lineage of the Emperor’s family could be directly traced back to the mythical creation of the country.

Kōki records time based from the enthronement year of the legendary First Emperor Jinmu, BCE 660. Based on an analysis of the Nihon-Shoki, the Meiji government decided that the Year 601 in the Gregorian calendar, when the Empress Suiko[2] moved the capital to Iruka, was the Year 1261 in Kōki. The Meiji Government calculated the reign of each Emperor before the Empress Suiko as described in Nihon-Shoki and concluded that the enthronement of the Emperor Jinmu was one thousand, two hundred and sixty years before 601 AD – hence, the start-point of BCE 660 (or Year One in Kōki).[3] According to Nihon-Shoki, the Emperor Jinmu ascended to the throne on the first day of the year and he ruled for sixty-six years, from BCE 660 to BCE 595 in Christian calendar.

The Kōki had been widely used before the Second World War, but nowadays, it is rarely used, and even then only by the older generation, Shinto priests, right wing people and some historians. To celebrate Kōki 2600, the Japanese Government tried to host the Olympic Games and a World Exposition.

But as it turned out, the Games were cancelled after the breakout of the Sino-Japanese War. Presently, the only remnant of Kōki 2600 is in the name of the most famous fighter plane of the Imperial Japanese Navy.[4] Even today, younger Japanese do not know what the Zero represented.

September, 2667

The author is a Ph.D. candidate at the Dept. of History in NUS. This is his third contribution after his take on the origins of Japanese curry and an introduction to several archives in Japan.

[1] The term Shintō (神道) was firstly used in Nihon-Shoki in which it refers to divinities, shrines and religious observance.

[2] The First Empress in Japanese history reigned from 554 to 628.

[3] Archaeological evidence has not proved the existence of the Emperor Jinmu. Archaeologist consider that the origin of the Imperial family could not be traced back beyond the Third Century.

[4] Other planes and tanks were also named after the year they were commissioned. For example, Type 96 Land-based Based Attack Aircraft (Mitsubishi G3M) represented Kōki 2596 and the Type 97 Te-ke (Small Tank) represented Kōki 2597.