Why the Royal Navy preferred external armor belts

Would larger 18-inch-gun ships need internal armor belts to save weight and fit infrastructure limits?

The Royal Navy preferred an external belt because damaged plates could be removed and replaced far more readily than internal armor.

Armor placement affects repairability as well as weight. British practice favored external belts because damaged plates could be stripped and replaced quickly after action, as in repairs to Prince of Wales following Denmark Strait. An internal belt may offer design advantages. Reaching it, however, can require cutting through surrounding structure before new armor can be installed.