Protected decks for a global-station cruiser

The armor scheme presents an apparent paradox: armor thickness had declined since HMS Warrior even as naval guns became more powerful. The Mersey design concentrated protection in a deck that thickened over boilers, engines, and magazines and tapered toward the ends. That deck also added structural strength, while coal stowage and a port-side passage shaped the protected internal arrangement. A nine-inch conning tower reflected expectations of close-range fighting, although it imposed a substantial weight penalty. Smaller rapid-fire weapons guarded against torpedo boats, and the resulting balance of protection, cost, and credible force suited routine deployment across the empire.