Type B3 submarine

Class overview
Name:	Type-B submarines
Builders:	Kure Naval Arsenal Sasebo Naval Arsenal Yokosuka Naval Arsenal Kawasaki Shipbuilding Mitsubishi Heavy Industries
Operators:	Imperial Japanese Navy
Preceded by:	Junsen type submarine
Subclasses:	Type-B (I-15 class) Type-B Modified 1 (I-40 class) Type-B Modified 2 (I-54 class)
Built:	1938-1944
In commission:	1940-1945

The Cruiser submarine Type-B (巡潜乙型潜水艦, Junsen Otsu-gata sensuikan) 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 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.

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 Type E submarine () (戊型潜水艦, Bo-gata sensuikan) 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 Type-E submarine (戊型潜水艦, Bo-gata sensuikan) from 1945 onwards

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