Type A submarine

The 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" ("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).
"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, the "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.
"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.
"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 in 1945.