Type B submarine

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Type-B submarines were Cruiser submarines used by the Imperial Japanese Navy in World War II. They were similar to the Type-A but lacked the headquarters installation.

Sub-classes
- S37: Twenty boats built between 1937 and 1944 under the Maru 3 and Maru 4 programs (boats 37–42 and 139–152).
- S37B: Six boats planned under the Maru Kyū program; all were completed.
- S37C: Twenty-one boats planned under the Maru Kyū and Kai-Maru 5 programs (boats 627–636 and 5101–5114); 18 were cancelled in late 1943 as the IJN shifted to Type-E submarines for 1945.
- S49A: Eighteen boats planned under Kai-Maru 5 (boats 5115–5132); all were cancelled in late 1943 for the same reason.

Builders
Kure Naval Arsenal, Sasebo Naval Arsenal, Yokosuka Naval Arsenal, Kawasaki Shipbuilding, Mitsubishi Heavy Industries.

In service
Built and commissioned 1940–1945. Operators: Imperial Japanese Navy. Preceded by Junsen Type A; succeeded by Junsen Type C.