A huge "Submarged aircraft carrier". Equipped with three Seaplane/attacker "Seiran".
Ships of this class : I-400, I-401, I-402 (I-402 was converted to submarine/oil tanker)

I-13 Class (also known as Junsen (1st) mod 2)

I-12 class submarine coverted to smaller submarged aircraft carrier. Equipped with two Seaplane/attacker "Seiran".

Ships of this class : I-13, I-14, I-15, I-1

I-201 Class

New high speed submarine built in 1944. Posseses high underwater speed (19kt) to escape depth charge attacks.
Ships of this class : I-201, I-202, I-203, I-204, I-205, I-206, I-207, I-208