Casemate ironclad

The casemate ironclad is a type of iron or iron-armored gunboat briefly used in the American Civil War. Compared to the traditional ironclad warship, 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 on 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 porting three layers of 2" steel) 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 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, 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" 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.