Japanese I-class submarines in their own period

Were Japan's I-class submarines ahead of their time?

Not necessarily; they were a variation on the cruiser-submarine concept and should be judged against the roles and ideas of their own period.

Historical submarine concepts should not be judged solely by modern expectations. Japan's I-class boats fit a contemporary family of cruiser-submarine ideas rather than representing a technology that simply arrived before its time. Designers were still testing several answers to what a long-range submarine should do and how it should support a fleet. The useful question is the role assigned to the boat within its own doctrinal and technological setting.