Tested the British U class abit in the mission editor.
I can confirm they can dive and surface -but they seem to a have a few problems with this in shallow depth. (they bottom out on occasion)
I have yet to see one make an attack with guns or torpedos.
Im my test mission i put a submerged U-class up against a german merchent (unarmed)
But the mission screwed up, 3 merchents and and 3 U-class were spawned (stacked on top of each other)
Some took and damage and sunk themselves as a result)
not sure what Im doing wrong.....
On a side note: the 3D model of the U-class is beautifully crafted.
