The four-shaft proposal is a genuine improvement over the three-shaft arrangement shown for an earlier design. More shafts spread horsepower and torque, helping a large ship sustain speed without pushing each shaft beyond the limits of contemporary metallurgy and fabrication. Nelson and Rodney provide a smaller example of how another shaft and its machinery could have raised speed within the available displacement. Shaft count is a question of durable power transmission, not simply a line on a specification table.
Notable Point · 32:24-34:20
Four shafts spread sustained-speed loads
Four shafts distribute power more safely when a very large battleship must sustain high speed without overloading its metallurgy.