Odd and even numbers in IJN submarine types

Why did the IJN use odd numbers for one submarine type and even numbers for another?

The convention likely made the type immediately recognizable from the reporting number alone.

The odd-even split was probably an information shortcut. A commander reading a boat number could infer its type without consulting a separate class list. That recognition helped staff decide where and how to position the reported submarine. The explanation remains a likely purpose rather than a documented certainty.