The correct answer is D) varying the angle of a tilting box or eccentricity of a floating ring. The rotation of the steering wheel on the navigation bridge initiates a change in the angle of a tilting box or the eccentricity of a floating ring. This change is then used to regulate the oil flow and pressure being applied to the steering gear rams, enabling the steering system to respond to the helmsman's input. The other options are incorrect because they do not accurately describe the mechanism by which the steering wheel input is translated into the required oil pressure for the steering gear. Options A, B, and C describe intermediate steps or components in the overall steering system, but do not directly explain how the wheel rotation initiates the oil pressure application.