I was in the US Navy decades ago, long before these digital systems. That said, there are many ways to control rudders, and for that matter engines, that don't rely on someone hooking up a block and tackle (although that actually was the method of last resort for destroyers, of course much smaller than these cargo ships). Taking "manual control" simply meant not running the steering directly from the bridge, e.g. instead running it from the hydraulic controls in after steering (a compartment directly above the rudders).
Exactly, ultimately there is always a point where the digital control meets up with the mechanical control that does the actual work. If the digital fails then you assess the mechanical control directly.
I was in the US Navy decades ago, long before these digital systems. That said, there are many ways to control rudders, and for that matter engines, that don't rely on someone hooking up a block and tackle (although that actually was the method of last resort for destroyers, of course much smaller than these cargo ships). Taking "manual control" simply meant not running the steering directly from the bridge, e.g. instead running it from the hydraulic controls in after steering (a compartment directly above the rudders).