The C-class attack boats were intended to work with A-type command submarines and B-type scouts. Their design developed the KD6 layout with two additional torpedo tubes, giving eight forward tubes in two torpedo rooms arranged one above the other. The C1 boats carried twenty torpedoes, a 5.5-inch deck gun and a twin 25 mm anti-aircraft mounting. They carried no aircraft, but fittings aft of the conning tower accommodated a Type A midget submarine. The design also offered improved underwater manoeuvrability over the KD6. In early 1943, I-16's conversion to supply work removed the deck gun and reduced torpedo reloads.
Chapter · 2:43:46-2:45:35
Japan's C1 attack submarines and their midget-submarine fittings
Eight bow torpedo tubes and midget-submarine fittings gave Japan's C1 boats a concentrated attack role, before supply conversions reduced their armament.