I will now do an exception and repost an old post from US forums (can’t remember who posted it first, I think it was SoukouDragon) about the way Japanese tanks are named, because I believe that’s an actual topic:
There were Two systems: Order System and Classification System, both of which are under the Army Imperial Year System.
Army Imperial Year System
The Imperial Year was used as the standard for designating the type, based on the mystical founding of Japan in 660 BC. The accepted practice was to use the last two numbers of the year as a type number, as in the Type 89 medium tank of 1929, with Type 100 for items accepted in 1940. After 1940 only the last digit was used, so Type 2 equipment was accepted in 1942.
Each tank is given a separate name, based on the order in adapation. The Type 89 medium tank was the “I-Go”, or “first car/model” while the Type 95 light tank was the “Ha-Go”, or “third car/model” (no second model has been identified).
Starting from the Type 97 Chi-Ha, the naming system was changed to incorporate the classification of the tank. Each tank would get a two letter name, with the first letter standing for the type of tank and the second for the order in which the tanks were developed.
The majority of tanks fell into three categories – Chi, Ke and Ho, or Medium, Light and Gun, with Chi and Ke used as single character abbreviations for Chiu (or Chui) and Kei. There seems to have been a category for Heavy (O, short for Oo), but this is only “confirmed” in the sense that it was the unofficial name given to the 120 ton tank O-I.
The numbering system used was based on the Iroha, a Japanese poem. This used every character from the Japanese syllabary once, and for a long time was used to put those characters in order (in a rather poetic version of the ABC). The first two lines of the poem, transliterated in roman letters, ran:
i ro ha ni ho he to
chi ri nu ru wo
If we summarize the naming system:
Ho: Gun (Tank Destroyer)
1- I or Yi
2 – Ro
3 – Ha
4 – Ni
5 – Ho
6 – He
7 – To
8 – Chi
9 – Ri
10 – Nu
11 – Ru
12 – O or Wo
Using the medium tanks as an example:
Chi-I (Medium First): None (most likely Experimental Type 1 Tank)
Chi-Ro (Medium Second): Type 89 I-Go
Chi-Ha (Medium Third): Type 97 Chi-Ha
Chi-Ni (Medium Fourth): Type 97 Chi-Ni (never got out of prototype status)
Chi-Ho (Medium Fifth) Type 98 Chi-Ho (never got out of prototype status)
Chi-He (Medium Sixth): Type 1 Chi-He
Chi-To (Medium Seventh): Type 4 Chi-To
Chi-Ri (Medium Ninth): Type 5 Chi-Ri
Chi-Nu (Medium Tenth): Type 3 Chi-Nu