Correct Chris! The Cable actually housed a "speedometer" type cable in US Boats. I imagine something similar was on the U-Boats. Since torpedos were mechanical in nature, all inputs were put in through this type of "transfer of data" to the fish. A settings were mechanical or hydro mechanical in nature. The Hydro mechanical were springs and diaphams with the springs being "adjusted" or set for depth by an increase or decrease of tension applied to the spring. The Run to "arm", and Gyro Angle input was off the shaft of the propellors to calculate distance traveled per revolution of the shaft. As electromechanical technology improved these cables were eventually replaced by servo motors attached directly attached to the tube. Eventually servo motors were installed in torpedos enabling an electrical umbilical cable to serve as the link between the fire control computer/TDC and the weapon.

Frank