Japanese imperial year

The or "national calendar year" is a unique calendar system in Japan. It is based on the legendary foundation of Japan by Emperor Jimmu in 660 BC. "Kōki" emphasizes the long history of Japan and the Imperial dynasty.
History.
"Kōki" dating was used as early as 1872, shortly after Japan adopted the Gregorian calendar system, and was popular during the life of the Meiji Constitution (1890–1947).
The Summer Olympics and Tokyo Expo were planned as anniversary events in 1940 ("Kōki 2600"); but the international games were not held because of the Second Sino-Japanese War. 
The Imperial Japanese Army (IJA, from 1927) and Imperial Japanese Navy (IJN, from 1929) used the "Kōki" system for identification. For example many Japanese names circa World War II use imperial years:
The Proclamation of Indonesian Independence (1945) used the imperial year ("Kōki 2605").
In Japan today, the system of counting years from the reign of Emperor Jimmu has been officially abandoned. Now the system is used in Shinto context only.