Type B submarine

The Cruiser submarine Type-B (巡潜乙型潜水艦) 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.

Class variants
The Type-B submarines were divided into four classes:
 * Type-B (乙型（伊十五型）)
 * Type-B Mod.1 (乙型改一（伊四十型）)
 * Type-B Mod.2 (乙型改二（伊五十四型）)
 * V22A Type (第5115号艦型). The 5115th vessel-class submarines were not built and remained a design only.

Type-B (I-15 class)
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).

Type-B Mod.1 (I-40 class)
Project number S37B. Six boats were planned under the Maru Kyū 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.

Type-B Mod.2 (I-54 class)
Project number S37C. Twenty-one boats were planned under the Maru Kyū 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 Bo-gata sensuikan (戊型潜水艦) as 1945's main submarines.


 * Boats in class

V22A Type
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 Type-E submarine (戊型潜水艦) from 1945.


 * Boats in class