Japanese subs were slow to dive, had rather shallow crush depth and were quite noisy, in general they were technically inferior compared to the subs of other major Navies but of course there were some advanced designs as well (the I-200 class for example achieved underwater speeds of 19 knots). Japanese subs divide into two main categories, the small coastal subs of the RO classes and the big fleet subs of the various I-classes, including the giant I-400 class. More here
http://en.wikipedia.org/wiki/Imperia...avy_submarines.