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A type of US Navy Ironclad, which was never completed. See Wikipedia.
1863 Extract from The Engineer: "The Stevens Battery (American), 6,000 tons, constructed of iron and nearly completed, is 420ft. long, 58ft. wide, and 28ft. deep from the top of the casemate, and is ironclad from end to end along the waterline. As proposed to the last Congress, the central casemate was to be about 120ft. long on the top, its sides being inclined 27.5 degs. from the horizon, and composed of 6.75in. of iron, 14in. of locust backing, and a half-inch iron lining. Upon the top of it, and to be loaded and manoeuvred from within it, were to be five 15-in. smooth-bores and two 10-in. rifled guns clad with armour. The actual horse-power of this ship being above 8,000, her speed would be much higher than that of any other war vessel. Congress, declining to make an appropriation to complete this vessel, made it over to Mr. Stevens, who had already borne a considerable portion of its cost, and who intends to finish it at his own expense, and is now experimenting to still further perfect his designs."