An insurance policy against Dreadnought risk

The class carried four 12-inch guns and ten 9.2-inch guns, a major step beyond the King Edward VII class. That mixed-calibre development ran through the Chilean-designed Swiftsure class, with 10-inch and 7.5-inch guns, and the King Edward VII class, which paired four 9.2-inch weapons with older 12-inch Mark IX guns. Lord Nelson combined ten 9.2-inch guns with the newer 12-inch Mark X, creating a powerful fallback if Dreadnought's long-range fire-control concept disappointed. At closer ranges, the faster-firing 9.2-inch weapons could deliver a more useful volume of fire, while a broadside could bring five of them and all four 12-inch guns to bear. Replacing vulnerable 6-inch casemate guns with a larger secondary calibre also reflected the expectation that heavy guns could disable lightly protected batteries before a decisive engagement developed.