Type B1 submarine
The , also called was the first group of boats of the Type B cruiser submarines built for the Imperial Japanese Navy (IJN) during the 1940s. In total 20 were built, starting with , which gave the series their alternative name. Design and description. The Type B submarines were derived from the earlier KD6 sub-class of the and were equipped with an aircraft to enhance their scouting ability. They displaced surfaced and submerged. The submarines were long, had a beam of and a draft of . They had a diving depth of . For surface running, the boats were powered  by two diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a electric motor. They could reach on the surface and underwater. On the surface, the "B1"s had a range of at ; submerged, they had a range of at . The boats were armed with six internal bow torpedo tubes and carried a total of 17 torpedoes. They were also armed with a single /40 deck gun and two single mounts for Type 96 anti-aircraft guns. In the Type Bs, the aircraft hangar was faired into the base of the conning tower. A single catapult  was positioned on the forward deck. Late in the war, some of the submarines had their aircraft hangar removed, to replace it with an additional 14 cm gun. In 1944, "I-36" and "I-37" had their aircraft hangar and catapult removed so that they could carry four Kaiten manned torpedoes, with "I-36" later being further modified to carry six. Service. The series was rather successful, especially at the beginning of the war. Losses. Altogether the Type B submarines (B1, B2, and B3 combined) are credited with sinking 56 merchant ships for a total of 372,730 tonnes, about 35% of all merchant  shipping sunk by Japanese submarines during the war. All B1 type submarines were lost during the conflict, except for "", which was scuttled off Gotō Islands by the US Navy on 1 April 1946.