Sen Yu Sho
The Sen Yu Sho (small supply submarine) were also referred to as the SS Type. These submarines were intended to be mass produced and replace losses of the larger D1/D2 submarines. They featured all welded, modular hulls that allowed for a short five-month construction time. They carried no torpedo tubes, but some could carry ten 18-inch torpedoes as cargo for resupply of midget submarines. They carried a 25-mm AA gun. Twelve boats were laid down of which 10 were completed before the end of the war. Another planned 88 were cancelled.
Type D2 (Tei-Gata 2)
This was a cargo submarine similar to Type D1, but with a stronger hull. She carried only one landing craft. I-373 was sunk by USS Spikefish (SS 404) about 190 miles southeast of Shanghai on 14 August 1945. A second hull, I-374, was scrapped before completion. Four others were canceled.