Editing Protected cruiser (section)

===First protective decks===

During the 1870s the increasing power of [[armour-piercing shell]]s made armouring the sides of a warship more and more difficult, as very thick, heavy armour plates were required. Even if armour dominated the design of the ship, it was likely that the next generation of [[shell (weapon) |shells]] would be able to pierce such armour. This problem was even more poignant where the design of cruising warships was concerned, with their requirement for long endurance needing much of their displacement to be devoted to consumable supplies – even where very powerful and space-consuming high-speed machinery was not required – leaving very little weight available for armour protection. This meant that effective side belt armour would be almost impossible to provide for smaller ships.

The alternative was to leave the sides of the ship vulnerable, but to armour a deck just below the waterline. Since this deck would be struck only very obliquely by shells, it could be less thick and heavy than [[belt armour]]. The ship could be designed so that the engines, boilers and [[Magazine (artillery)#Naval magazines |magazines]] were under the armoured deck, and with hopefully enough reserve buoyancy to keep the ship afloat even in the event of flooding resulting from damage above the protective deck.<ref>Beeler, pp. 42–44</ref> An armoured deck had actually been used for the first time in HMS ''Shannon'', although she did rely principally on her vertical belt armour for defence: Her protective deck was only a partial one, extending from the forward armoured bulkhead of the [[armoured citadel|citadel]] to the [[Bow (ship) |bow]].