The control helm on a U-boat is right where the "chief" is standing. It should look like a box with two buttons on top, the box saying "BBC."
There should be another "BBC" box in the "bridge", right next to the Watch Officer.
edit: per dictionary.com:
helm:
noun
1. Nautical .
a. a wheel or tiller by which a ship is steered.
b. the entire steering apparatus of a ship.
c. the angle with the fore-and-aft line made by a rudder when turned: "15-degree helm".
2. the place or post of control: A stern taskmaster was at the helm of the company.
In short, it is both the "wheel" or apparatus, as well as the station that controls the heading of the ship. In the US Navy, "Helm, make your course three-five-zero." "Make my course three-five-zero, aye." (then the helm turns the rudder to accomplish the ordered course)