Casemate ironclad

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Casemate Ironclad USS Cairo on a contemporary photograph.
Casemate Ironclad USS Cairo on a contemporary photograph.

The casemate ironclad is an iron or iron-armored gunboat briefly used in the American Civil War. Compared to the traditional ironclad, the casemate ironclad does not have its cannons in an armored gun deck, but has an -often sloped- casemate structure on the main deck in which the guns are housed. As the guns are carried on the top on the ship, yet still fire through fixed gunports, the casemate ironclad is seen as an intermediate stage between the traditional broadside frigate, the ironclad gunship and the modern warships.

CSS Palmetto State, the archetypical casemate ironclad. Note the sloped deck and the low waterline
CSS Palmetto State, the archetypical casemate ironclad. Note the sloped deck and the low waterline
Detail of the remains of the USS Cairo as a museum ship today.  The sloped casemate deck is clearly visible.
Detail of the remains of the USS Cairo as a museum ship today. The sloped casemate deck is clearly visible.

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 like in classical warships. The casemate was heavily armored (Later confederate ironclads porting three layers of 2’’ steel) and was sloped so it could deflect direct hits (a 35 degree angle quickly becoming standard). Armor was also applied to the part of the hull protruding from the waterline. The casemate was often box-shaped with octagon (diamond-) shaped casemates 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 pulley-masts, flagpoles, davits and awnings were added on a temporary bases. Inside the casemate, the guns were housed in one continuous deck. Unlike later turret ironclads, the guns had to fire through fixed gunports and therefore aiming was done by moving the gun itself relative to the gunport. This was intensely labor-intensive and often up to 20 men were needed to load, aim, fire and clean a gun and even with this manpower it took more than five minutes after one shot before the gun was ready to shoot again.

Although the Union successfully used a fleet of casemate ironclad riverboats in their Mississippi Campaign, the casemate ironclad is mostly associated with the Confederacy. This is partly due to the Battle of Hampton Roads, between the Union turreted ironclad USS Monitor and the Confederate casemate ironclad CSS Virginia (AKA the Merrimack), which gave rise to the popular notion that "The North had Monitors 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.