Editing Duncan-class battleship (section)

===Armour===
The ''Duncan'' class adopted the basic armour layout of the ''Formidable'' class, but with significant revision to the forward armour scheme and with significantly thinner levels of protection. Earlier battleship designs had employed a partial armoured belt that terminated abreast of both of the main battery turrets; the ends of the belt were connected by way of transverse bulkheads to create a central citadel that protected the ships' magazines and propulsion machinery spaces. This arrangement left the bow and stern unprotected, and thus highly vulnerable to enemy fire. White was concerned that the unprotected bow could be flooded by even light gunfire, which would reduce speed and maneuverability. Since the ''Duncan''s were intended to serve as fast battleships, White decided to reduce the risk of this kind of damage by discarding the forward transverse bulkhead in favor of a complete belt. The main portion of the belt was {{convert|7|in|0}} thick and extended to just forward of the fore turret, thereafter being gradually reduced to {{convert|5|in|0|abbr=on}}, then {{convert|4|in|0|abbr=on}}, then to {{convert|3|in|0|abbr=on}}, and finally to {{convert|2|in|0|abbr=on}} close to the stem. The aft end of the ship retained the traditional transverse bulkhead, which was also 7&nbsp;in thick. Abaft of the bulkhead, the hull was protected by a [[strake]] of {{convert|1|in|adj=on}} thick side armour.{{sfn|Burt|pp=234–235}}

Horizontal protection consisted of a pair of armoured decks that covered the ships' vitals. The main deck ran from the stem to the aft bulkhead and was connected to the top of the belt; it was 1 to 2&nbsp;in thick, with the thicker armour over the central portion of the ship and the thinner steel over the bow. The second deck, at middle deck level, was 1&nbsp;in thick and covered just the central citadel, sloping down on the sides to the belt. The voids created between the decks and behind the belt were used to store coal, which had the added benefit of increasing the strength of the side protection layout. The bow and stern had a curved armour deck below the waterline that extended from the barbettes to either end of the hull, which was 1 to 2&nbsp;in thick. The ships' main battery turrets faces and sides were {{convert|8|in|0|abbr=on}} thick, with {{convert|10|in|abbr=on|0}} rears and 2–3&nbsp;in roofs. The turrets sat atop barbettes that were {{convert|11|in|abbr=on|0}} on the outer face above the belt and 7&nbsp;in thick behind the belt; their inner faces were reduced to 10 and 4&nbsp;inches thick, respectively. The casemate battery was protected with {{convert|6|in|abbr=on|0}} of armour plate, and their ammunition hoists received 2&nbsp;in of armour protection. The ships' forward [[conning tower]]s had 10–12&nbsp;in sides and their aft conning towers had 3&nbsp;in sides.{{sfn|Burt|pp=235–236}}