Keltos has made a wonderful series of playable Japanese subs, and is still refining and working on more!
They are playable through the U Boat missions add-on. At this stage a Japanese Campaign is being developed too, and is making great progress
so you can enjoy the great work of Peabody, Keltos and others soon(ish) with luck.
WATASHI MO, NIHON KAIGUN DAISUKE!