''This was an independently developed "Special Submarine" that was an improvement over the previous late-model.<br>It is an enlarged version of the Type-A Midget Submarine with increased cruising range and communications capability. With the crew count increased to 5 members and 2 bow-mounted 45 cm torpedo tubes, this is closer to a mini-submarine than an improved midget submarine.<br>It was originally designed to be operated from a ship, but this improved model can operate independently to support other ships.