Ironclad warship originally designed for use in shallow harbours and rivers to blockade the Confederate states in the American Civil War. The original ironclad, built by John Ericsson, was named Monitor Its innovative design included minimal exposure above the waterline, a heavily armoured deck and hull, and a revolving gun turret. The inconclusive Battle of the Monitor and Merrimack (1862) was the first between ironclad warships. Never seaworthy, the Monitor sank during a gale off Cape Hatteras that same year, but the U.S. Navy built many improved monitors during the war. The British navy kept its monitors in service as late as World War II.

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