The casemate ironclad is a type of iron or iron-armored gunboat briefly used in the American Civil War. Compared to the turreted ironclad warships that became standard, the casemate ironclad does not have its cannons in an armored gun deck, but instead has a casemate structure (often sloped) on the main deck housing the guns. As the guns are carried on the top of the ship yet still fire through fixed gunports, the casemate ironclad is seen as an intermediate stage between the traditional broadside frigate and the modern warships.
In its general appearance, a casemate ironclad consisted of a low-cut hull with little freeboard, upon which an armored casemate structure was built. This casemate housed anywhere from 2 to 15 cannons, most of them in broadside positions as in classical warships. The casemate was heavily armored (later Confederate ironclads had three layers of 2" steel) over heavy wood backing and was sloped to deflect direct hits (a 35-degree angle quickly becoming standard). Armor was also applied to the part of the hull above the waterline. The casemate was often box-shaped, with octagon shapes appearing in the later stages of the war. From the top of the casemate protruded an armored lookout structure that served as a pilothouse, and one or two smokestacks.
The casemate ironclad being steam driven, either by screws or by paddle-wheels, it did not need sails or masts, although sometimes, when not in combat, temporary pulley-masts, flagpoles, davits, and awnings were added. Inside the casemate, the guns were housed in one continuous deck. Unlike with turret ironclads, the guns had to fire through fixed gunports and therefore aiming was done by moving the gun relative to the gunport. This was labor-intensive and often up to 20 men were needed to load, aim, fire, and clean a gun, and even with this manpower the firing rate was no better than one shot per five minutes.
Although the Union successfully used a substantial fleet of casemate ironclad riverboats in their Mississippi and Red River Campaigns, the casemate ironclad is mostly associated with the Confederacy. This is partly due to the Battle of Hampton Roads, in which the Union turreted ironclad USS Monitor and the Confederate casemate ironclad CSS Virginia (sometimes called the Merrimack) dueled, giving rise to the popular notion that "The North had Monitors (predominantly deployed for coastal operations, whereas the unseaworthy Union casemate ironclads were restricted to inland river operations – hence their "brown-water navy" nickname) while the South had (casemate) ironclads". In effect, the Confederacy concentrated its efforts on casemate ironclads as a means to harass the Union blockade of their ports, but this was a choice dictated by available technology and materials rather than by confidence in the possibilities of this type.
In their specific outer appearances, i.e. being essentially floating gun batteries encased in armored citadels, albeit powered, the low-freeboard Union and Confederate casemate ironclads were uniquely American, but the concept of a fixed armored citadel mounted on a warship, housing the main armament, was further explored by European navies in the last quarter of the 19th century, by the French and British navies in particular, in no small part due to the inspiration gained from the Battle of Hampton Roads. This resulted in larger, high-freeboard ironclad frigates or battleships the British dubbed "centre battery ships" and the French "casemate" or "barbette" (if the citadel was circularly shaped) ships, which were oceangoing, unlike the American originals (excepting the Confederacy's CSS Stonewall, the only Confederate high-freeboard barbette/casemate ironclad, and the Union's, rather unusual low-freeboard, but oceangoing, casemate ironclad USS Dunderberg). British examples were among others HMS Bellerophon (the first such one completed by the British in 1865) and HMS Hercules (1868). French examples included Brasil (casemate, and as the name implies, completed for the Brazilian Navy in 1865, and when stripped of its masts, sharing a striking side profile similarity with its Confederate progenitors) and Redoutable (barbette, and the first warship in history to be constructed in steel in 1878, instead of iron). Still, all admiralties concluded that it was an evolutionary dead end and that the revolving gun turret was the way to go – the validity of the conclusion being amply hammered home when the revolutionary HMS Dreadnought (1906) entered service, rendering everything that went before obsolete overnight. As a result, by 1910 no navy had any casemate warship left in service.
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