The Type A1 submarine (巡潜甲型潜水艦, Junsen kō-gata sensuikan, "Cruiser submarine type A"), also called I-9-class submarine (伊九型潜水艦, I-kyū-gata sensuikan) were...

four classes: Type-A (甲型（伊九型）, Kō-gata, I-9-class) Type-A Mod.1 (甲型改一（伊十二型）, Kō-gata Kai-1, I-12-class) Type-A Mod.2 (甲型改二（伊十三型）, Kō-gata Kai-2, I-13-class)...