Monitor

1. A turreted ironclad warship of the second half of the 19th century characterized by low freeboard, shallow draft, poor seaworthiness, and heavy guns, intended for riverine and coastal operations.
2. In occasional 19th-century usage, any turreted warship.
3. A shallow-draft armored shore bombardment vessel of the first half of the 20th century, designed to provide fire support to ground troops, often mounting heavy guns.
4. (breastwork monitor) A 19th-century monitor designed with a breastwork to improve seaworthiness.
5. (river monitor) A monitor specifically designed for riverine operations, used during the 19th and 20th centuries and more recently than other types of monitor. River monitors generally are smaller and lighter than other monitors.