Nelson-class armour came at the price of speed

Rodney and Nelson were heavily protected frontline battleships whose central operational weakness was speed. A faster design derived from the F3 battlecruiser concept might have produced a roughly 28-knot battleship. The alternative would have sacrificed some protection density, though it need not have abandoned the desired gun calibre because the proposed 15-inch/50 and adopted 16-inch/45 weapons were not radically different in weight. The result was a pair of powerful ships whose machinery was always being asked to recover capability the design had traded away. That interwar design choice constrained Royal Navy employment for the next two decades.