The USS Monitor was an iron-hulled steamship—the first ironclad warship commissioned by the Union Navy. The need for iron plating on ships only arose after the shell-firing cannon was introduced to naval warfare in the 1820s. (The motivation to build the Monitor was prompted by the news that the Confederates were building an ironclad warship, named Virginia.) Constructed in Long Island in just 101 days, the ship’s machinery, plates, and other iron work were manufactured in Troy, NY.
Troy industrialists John Winslow and John Griswold has the contract with the US government. They called on their connections with Adirondack iron companies for supply. Iron for the Monitor came from several sources, including Crown Point, Roth’s Forge at North Hudson, and some from the ore mined at 21 Pit by the Port Henry Iron Ore Company. The ship was launched on January 30, 1862, and defeated the Virginia (formerly the Merrimac) on March 9. Eventually, six more vessels of the same type were built.