check this out
http://uboat.net/types/xb.htm will make your eyes bulge
Type XB
"These boats were laid down as ocean-going submersibles, designed in 1938. They could carry up to 66 SMA mines in 30 mine shafts and up to 15 torpedoes. The XB class was special for that they only had two torpedo tubes at the stern. As transport boats 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). At 2710 tons submerged and fully loaded they were the largest German U-boats ever built and they paid a penalty in diving speed and agility. 6 of the 8 boats built were sunk during the war (5 with all hands) but two survived the war."
