If you're really pissed off about having this...There's a great Type XXI mod here. It gives a snorkel, deck guns, and a new skin to the Walther. (And removes the turbine).
http://www.subsim.com/radioroom/show...ied+type+xviii
NOTE: Putting ROW #3a over the mod will remove the deck guns, keep the snorkel, and add the walther back in. If that's your deal, go ahead with overwriting it.