Type A submarine

The Cruiser submarine Type-A (巡潜甲型潜水艦) was a class of submarine in the Imperial Japanese Navy (IJN), which served during the Second World War. The Type-A submarines were built to take a role of the command ships for submarine squadrons. For this reason they had equipment for a headquarters, better radio facilities and a floatplane.

Class variants
The Type-A submarines were divided into four classes:
 * Type-A (甲型（伊九型）)
 * Type-A Mod.1 (甲型改一（伊十二型）)
 * Type-A Mod.2 (甲型改二（伊十三型）)
 * V21 Type (第5094号艦型). The 5094th vessel class boats were not built and remained only a design.

Type-A (I-9 class)
Project number S35Ja. Their design was based on the Junsen III (I-7 class). Three boats were built in 1938-42 under the Maru 3 Programme (Boat # 35 - 36) and Maru 4 Programme (Boat # 138).


 * Boats in class

Type-A Mod.1 (I-12 class)
Project number S35B. Five boats were planned under the Maru Tsui Programme (Boat # 620 - 621) and the Kai-Maru 5 Programme (Boat # 5091 - 5093). They were equipped with less powerful diesel engines which shortened the time needed to build them. Only one boat, JAPANESE SUBMARINE I-12, was completed to the original design. The I-13 and the later boats were converted to a new submarine class (I-13 class), because the number of I-400 class boats was reduced.
 * Boats in class

Type-A Mod.2 (I-13 class)
Project number S35C. Four boats were planned under the Maru Tsui Programme (Boat # 621) and the Kai-Maru 5 Programme (Boat # 5091 - 5093). However, four boats were converted to new submarine class (I-13 class), because a number of submarines of the I-400 class were cancelled. They had a large hangar and were equipped with bulges to be able to operate 2 × special Aichi M6A1 Seiran attack bombers. The headquarters institutions were removed.


 * Boats in class

V21 Type
Project number S48. Three boats were planned under the Kai-Maru 5 Programme. However, all boats were cancelled in late 1943, because the IJN turned its attention to the construction of Bo-gata sensuikan (戊型潜水艦) in 1945.


 * Boats in class