A monitor was the class of relatively small warship which was neither fast nor strongly armoured but carried disproportionately large guns. They were used by some navies from the 1860s until the end of World War II, and saw their final use by the United States Navy during the Vietnam War.The original monitor was designed by John Ericsson in 1861 who named it USS Monitor. They were designed for shallow waters and served as coastal ships. The term ""monitor"" also encompassed more flexible breastwork monitors, and was sometimes used as a generic term for any turreted ship.""Monitor"" also represents the strongest of riverine warcraft, known as river monitors. In the early 20th century, the term ""monitor"" was revived for shallow-draft armoured shore bombardment vessels, particularly those of the Royal Navy: the Lord Clive-class monitors carried guns firing heavier shells than any other warship ever has, seeing action (albeit briefly) against German targets during World War I. The Lord Clive vessels were scrapped in the 1920s.