Board Thread:Wikia Discussion/@comment-25683568-20150318062713/@comment-25683568-20150621030557

See, that's where you're wrong. Xth Year Type is a different thing altogether. Xth Year Type = X年式, which was used for equipment entering service/developed in the Taisho (大正) period, drawing the number from a different year format, the year of the Taisho period. For example, an equipment entering service in 1914 (Japanese imperial year 2574) would be assigned the name 三年式, or 3rd Year Type, as it is the 3rd year of the Taisho period. Whereas an equipment entering service in 1931 (6th year of the Showa period) would be assigned the name 九一式, or Type 91.

What's wrong with Bi? The name of the equipment is literally 毘式(びしき).