A total of eight Type XB boats were produced, which replaced the mine chamber of the projected Type XA with six vertical wet storage shafts in the forward section of the hull. Up to 18 mines could be carried in these shafts, with an additional 48 mines in a series of 12 shafts set into the saddle tanks on each side. They only had two torpedo tubes, both at the stern. When used as cargo-carrying submarines they carried freight containers in the mine shafts (or had the freight containers welded on top of the lateral shafts, preventing their use for mines).