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 and the Confederate casemate ironclad (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. Since breaking the Union blockade was the primary objective of the Confederacy's casemate ironclads, as outlined in a May 1861 letter from its Secretary of the Navy Stephen Mallory (who was the one who came up with the idea of employing ironclads to offset the numerical superiority of the Union Navy in the first place) to the Confederate House Committee on Naval Affairs, the majority of them were from the outset designed to operate in coastal waters as well as inland waters, and unlike their Union counterparts were, theoretically at least, seaworthy to a limited extent – since they were never expected to venture out onto the high seas. This was exemplified by the fact that most Confederate ironclads were designed with a keeled deep draft hull, as opposed to the Union shallow draft flat bottom hulls (also featured on the Confederate river ironclads of which there were also a number built). This came at a cost however, Confederate coastal ironclads frequently ran aground when operating in inland waters or shallow coastal waters, with more than one being captured by the Union because of it, or being destroyed by their own crews to prevent capture in such circumstances – a fate that befell the CSS "Virginia" as her draft ultimately prevented her escape some time after the Battle of Hampton Roads.