ironclad, mid-19th-century wooden warship protected from gunfire by iron armor. The success of the ironclad when first employed by the French in the Crimean War sparked a naval armor and armaments race between France and Great Britain. Ironclads were later used by both sides in the U.S. Civil War (see monitor, Monitor and Merrimack), although only the Union navy had at its disposal sufficient industrial resources to build a sizable fleet. The armored ship became obsolete with the introduction (1870-90) of all-metal warship construction.

Type of warship developed in Europe and the U.S. in the mid-19th century, characterized by the iron armour that protected the hull. In the Crimean War (1853–56) the French and British successfully attacked Russian fortifications with “floating batteries,” ironclad barges mounting heavy guns. In 1859 the French completed the first iron warship, the Gloire; its iron plates, 4.5 in. (11 cm) thick, were backed by heavy timber. Britain and the U.S. soon followed. Union forces launched armored gunboats on the Mississippi at the start of the American Civil War, and a flotilla captured Fort Henry (1862). The first battle between ironclads was the Battle of the Monitor and Merrimack (1862). Later refinements led to the battleship. Seealso monitor.

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