Japan has another era "Kouki(皇紀）" compared with the christian ere.
CIA's web page "The World Face book" says that "Japanese independent is 660B.C".
Kouki 2600 is equal to A.D. 1940. (660+1940=2600)
Zero fighter's name "Zero(ゼロ戦 or 零式艦上戦闘機）" is based on Kouki 2600(when it's operation began).
IJA 97-shiki fighter was emplyed in December Kouki 2597(A.D.1937, Showa 12).
1-shiki fighter Hayabusa(隼 or Oscar) was employed in Kouki 2601(1941).
Shiki(式） means "type".
Just adding to the above posts, Japanese designations started using the Kouki year count when the Showa Era began, in 1926. Previously, the designations were based in the then-current era year count(e.g. Arisaka Type 38 Rifle entered service on the 38th Year of Meiji - 1905; Type 4 15cm Howitzer entered service on 1915 - 4th Year of Taishou). Also, Type 0 was the IJN designation for aircraft/weapons that entered service on 1940; the IJA designation was Type 100(e.g. Type 100 Submachinegun).