I can’t actually provide you any information on your German submarine. However, there was also a British submarine (the M2) which was converted to carry a small biplane that sank with of all of its crew in 1932. You can find a diving related article about the submarine at
http://www.divernet.com/wrecks/wtour5799.htm . It is regularly visited to this day by divers, although it not possible to enter the submarine, other than the hanger. As it is obviously considered to a military grave.