Sloppy research, calling Japanese subs I-class is like calling all German subs U-class, More accurate would be to refer to them as classes by the complete lead boat number (ex. I-400 class) or their Japanese classes (ex. for I-400 ST or Sen-Toku), much as we refer to the German U-boats by theirs (ex. Type VII for the smaller boats off Britain and in the Med or the big Type IX's that hunted off our own coasts.
Nothing secret or forbidden-knowledge here, just little known for people who skipped or slept through History class. A better term would be "Forgotten." Almost ALL Japan's subs carried either a floatplane or a minisub, mainly because Japanese doctrine was to use their subs as scouts and harassers as they tried to draw the American fleet into the Decisive Battle they sought... here again they were tactically clever but strategically foolish; even after Pearl and the Indian Ocean carrier raids they clung to the big-gun battleship as the primary arm-of-decision while we took the lessons of Pearl, fully embraced them and made carrier aircraft the "Fist of the Fleet."
Professional military historian here, WWII Pacific (more specifically SWPA) specialist.