United States Ironclads

The United States Navy built and operated several classes of ironclad warships during and after the Civil War. These included ocean-going armored frigates, armored gunboats, and turreted vessels. The famous battle between the USS Monitor and the CSS Virginia in 1862 became a defining moment in naval history and introduced the world to the era of the armored warship.

While the term *ironclad* covers a wide range of armored vessels, *monitors* represented a specific type of ironclad warship characterized by their low freeboard, rotating gun turret, and heavy armament. The success of the USS Monitor led to the construction of several monitor classes in the United States Navy, but other ironclad designs continued to play important roles in coastal defense, river operations, and fleet development.

This section provides an overview of the United States Navy’s ironclad warships, including their classes, individual ships, technical characteristics, and historical service. Together, these vessels represent the transition from the age of sail to the modern era of steam-powered and armored naval warfare.

Early / Seagoing Ironclads

Monitors were a specific type of ironclad warship characterized by their low freeboard and rotating armored turret. Although monitors are classified as ironclads, they represent a separate design concept from traditional broadside ironclads. For a complete overview of US Navy monitors, see the dedicated US Monitors page.

Early Seagoing Ironclads and Experimental Designs

Passaic class

The Passaic-class ironclad monitors of the U.S. Navy saw service in the U.S. Civil War and the Spanish–American War. The class was an improved version of the USS Monitor equipped with a 15-inch Dahlgren gun in place of one of the 11-inch guns.

Canonicus class

The Canonicus-class or Tippecanoe-class was a class of nine monitors built for the Union Navy during the American Civil War. An improvement on the preceding Passaics, modified in accordance with war experience, each vessel mounted two 15-inch guns. The five ships commissioned during the war participated variously in the Bermuda Hundred Campaign, the Battle of Mobile Bay and the First and Second Battles of Fort Fisher. When attacking the ironclad ram CSS Tennessee in 1865, the monitor Tecumseh was sunk by a naval mine, then termed a “torpedo”, 94 men died.

River Ironclads

City class

The Pook Turtles, or City-class gunboats to use their semi-official name, were war vessels intended for service on the Mississippi River during the American Civil War. They were also sometimes referred to as “Eads gunboats.” The labels
are applied to seven vessels of uniform design built from the keel up in Carondelet, Missouri shipyards. The City-class gunboats were the United States’ first ironclad warships.

The gunboats produced by Eads formed the core of the United States Army’s Western Gunboat Flotilla, which later was transferred to the US Navy and became the Mississippi River Squadron. Eads gunboats took part in almost every significant action on the upper Mississippi and its tributaries from their first offensive use at the Battle of Fort Henry until the end of the war.

Other Union River class Ironclads

River Ironclads / Monitors

Neosho and Milwaukee class and USS Ozark

The Neosho-class monitors were a pair of ironclad river monitors laid down in mid-1862 for the United States Navy during the American Civil War. After completion in mid-1863, both ships spent time patrolling the Mississippi River against Confederate raids and ambushes as part of the Mississippi Squadron. Osage was grounded on a sandbar for six months after the end of the campaign while Neosho resumed her patrols on the Mississippi. Osage, after being refloated and repaired, was transferred to the West Gulf Blockading Squadron in early 1865. During the Battle of Spanish Fort in March 1865 she struck a mine and rapidly sank.

The Milwaukee-class monitors were a class of four riverine ironclad monitors built during the American Civil War. Several supported Union forces along the Mississippi River in mid-1864 before participating in the Battle of Mobile Bay in August. Chickasaw and Winnebago bombarded Confederate coastal fortifications during the battle and during subsequent operations as well as engaging the ironclad Tennessee II. The other two ships arrived at Mobile Bay after the battle and all four supported the land attacks on Mobile in March–April 1865. Milwaukee struck a torpedo during this time and sank. The surviving three ships were sold in 1874; Chickasaw was converted into a ferry and survived until 1944 when she was scuttled. Her wreck was discovered in 2004.

USS Ozark was a single-turreted river monitor built for the United States Navy during the American Civil War. The ship served in the Mississippi River Squadron during the war. Ozark patrolled the Mississippi River and its tributaries after the end of the campaign for the rest of the war. She was decommissioned after the war and sold in late 1865. Her ultimate fate is unknown.

Miantonomoh class

The Miantonomoh class consisted of four monitors built for the Union Navy during the U.S. Civil War, but only one ship was completed early enough to participate in the war. They were broken up in 1874–1875.

Casco class (light-draft monitors)

The Casco-class monitor was a unique class of light draft monitor built on behalf of the United States Navy for the Mississippi theatre during the American Civil War. The largest and most ambitious ironclad program of the war, the project was dogged by delays caused by bureaucratic meddling. Twenty ships of the class were eventually built at great expense, but proved so unseaworthy when trialed that they were quickly sidelined, causing a public scandal.

Marietta class

The Marietta-class monitors were a pair of ironclad river monitors laid down in the summer of 1862 for the United States Navy during the American Civil War. Construction was slow, partially for lack of labor, and the ships were not completed until December 1865, after the war was over. However the navy did not accept them until 1866 and immediately laid them up. They
were sold in 1873 without ever having been commissioned.

Kalamazoo class

The Kalamazoo-class monitors were a class of ocean-going ironclad monitors begun during the American Civil War. Unfinished by the end of the war, their construction was suspended in November 1865 and the unseasoned wood of their hulls rotted while they were still on the building stocks. If the four ships had been finished they would have been the most seaworthy monitors in the US Navy. One was scrapped in 1874 while the other three were disposed of a decade later.

Capatured Confederate Ironclads in US Navy service