Look like they might be fun to build, but I bet you getting decent research on them will be a pain in the ass. I've only got one book with info on Jap subs in it and I don't recall seeing a lot of stuff about them. Probably won't stop me having a crack at one though, even though Jap subs do mostly look like German and Italian ones. That'll be my wife moaning again then, our house already looks like an unofficial annex to the Imperial War Museum as it is...
Chock