Gibs has erm..*cough* a U-Cruiser it's a type IX with 5 105mm DG's
So in theory these X-craft could be possible.
With regards to the XI
The projected specifications of the Type XI U-Cruiser were:
Length (oa):115 meters
Width: 9.5 meters
Draught: 6.2 meters
Displacement: 3 630 tons.
Propulsion: 2-shaft diesel/electric motors,(eight 12cyl. diesel engines in two separate engine rooms plus two electric motors in a seperate compartment).
Armament: 4 bow TT.
2 stern TT.
4 X 12.7cm cannon in two twin armored turrets.
2 X 3.7cm AA cannon.
2 X 2 cm AA mounted in Wintergarten.
1 X Arado reconnaissance seaplane.
Crew: 110 men, plus capacity to carry approximately 60 Brandenburgers.