The was a class of submarine in the Imperial Japanese Navy (IJN) which served during World War II. The Type-B submarines were similar to the Type-A apart from not having the headquarters installation.
The Type-B submarines were divided into four classes:
Project number S37. Twenty boats were built between 1937 and 1944 under the Maru 3 Programme (Boats 37 - 42) and Maru 4 Programme (Boats 139 - 152).
Project number S37B. Six boats were planned under the Maru Kyà « Programme (Boats 370 - 375), all boats were completed. On the outside this class looked the same as the I-15 class; however, they were built from high-tensile strength steel and equipped with diesel engines of a simpler design.
Project number S37C. Twenty-one boats were planned under the Maru Kyà « Programme (Boats 627 - 636) and Kai-Maru 5 Programme (Boats 5101 - 5114). Eighteen boats were cancelled in late 1943, because the IJN was setting the as 1945's main submarines.
Project number S49A. Eighteen boats were planned under the Kai-Maru 5 Programme (Boats 5115 - 5132). However, all boats were cancelled in late 1943, because the IJN concentrated on production of from 1945.