On most of the ships, you have :
- Engine power control,
- Rudder control,
- Bow thruster control.
I suppose you're talking about the bow thruster control, this is a transversal engine, a few meters behind the bow, whose purpose is to help the ships to turn, and to move sideways (combined with the main engines and rudders, off course). The bow thrusters are only effective at speeds below 4 or 5 knots.
You can find more details here :
http://en.wikipedia.org/wiki/Bow_thruster