CSS Louisiana was begun by E. C. Murray at New Orleans in mid-October 1861, but lack of materials impeded her completion. She was designed for four engines, two paddle-wheels in a center-well and two propellers, with twin rudders. Her casemate — all four sides sloping sharply at nearly a 45° angle — extended her full length, less 25 feet at each end, and was covered by "T" railroad iron in two courses, while its top was encompassed by sheet iron bulwarks nearly four feet high. On 20 April 1862 after Union mortar boats under Commodore David D. Porter, USN, had been shelling Fort St. Philip and Fort Jackson incessantly for two days; Louisiana, although unfinished and unready for action, was towed to Fort St. Philip. There, in anticipation of a Federal drive past the forts, up the lower Mississippi and into New Orleans, she was to participate with the Confederate naval force, in conjunction with the River Defense Fleet and the forts, in defending the passage to the city.
Louisiana, still incomplete, had insufficient power to maneuver as a warship in any naval action. The tandem installation of her paddle wheels was a major design blunder; underway the rear paddle had beat against the wash and foam of the front, severely-limiting the ship's power and speed. While waiting for the propellers to become operational, Captain J. K. Mitchell, CSN, commanding the naval forces in the lower Mississippi, decided that she should be operated as a floating battery. Accordingly he had her tied to the eastern bank of the Mississippi a half mile above Fort St. Philip. With mechanics on board working furiously night and day to prepare her batteries for action, Louisiana lay just clear of the line of fire of Commodore Porter's mortar boats which continued bombarding the forts.
On 24 April 1862, Flag Officer David G. Farragut, USN, ran his fleet past the forts on his way to capture New Orleans. Almost all of the Confederate ships were destroyed in the action. Louisiana, under Comdr. C. F. McIntosh, CSN, might have posed a serious threat to the Union fleet, but her lack of maneuverability and the inadequacy of some of her gun mountings which limited the direction of her fire made it impossible for the Confederates to make use of her full potential. Yet, for the most part the ironclad remained impregnable, and posed a constant danger to any Federal ship coming within her range and line of fire. USS Iroquois which came against her delivered a full broadside at a distance of a few feet, but did her little serious damage, while she herself was riddled by Louisiana's fire.
After Farragut's fleet passed the forts on 24 April, Commander Porter remained in the lower Mississippi with his mortar boats, completely isolating the Confederate force. Meanwhile Captain Mitchell worked frantically to get Louisiana's propellers ready for service so that she might sail effectively against the Federals. On 28 April 1862 just before this work was completed, the forts, with their communications cut off, surrendered to Commander Porter. Captain Mitchell, realizing that the defeat of his force was now inevitable, and not considering himself bound by the surrender of the military garrison, set fire to Louisiana and retired on her two tenders to the opposite bank, where he was later captured. Meanwhile, as the articles of capitulation of the forts were being drawn up under flags-of-truce on board Commander Porter's flagship, the burning Louisiana broke loose and drifted downstream. Her guns fired as the flames reached their charges, and then the whole ship exploded violently in front of Fort St. Philip, and was seen and heard for many miles.
The wreck of CSS Louisiana was discovered during a NUMA expedition in November, 1981, by author Clive Cussler. It rests under the shoreline mud near what was once the southeastern embankment of Fort St. Phillip; at present there are no plans to recover and restore the vessel.