Why all the complaining? I like the IX-D2 and i think they made a good job making the U-boat mission. The XVIII is there, so what. Screw the whole boat and play with the type9.... Thats what i do.
With all the skilled and very very capable modders, i am sure it can be worked out in one or another way.
My opinion is that they made a pretty darn good looking and cool IV-D2.
I sure dont disagree with you about the walter-thingie

...(the XXI would been cooler)
No hard feelings towards any of you, just take the good things and use it