Civil War Ironclads: Monitor Type Ships

This entry is part 8 of 10 in the series The Civil War at Sea

Civil War Ironclads: Monitor Type Ships

The Union Navy used both casemate type and monitor type ironclads. This post will cover the Monitor class ships that were pioneered by the Union Navy.

The Union Navy initially used a design by Swedish-born John Ericsson that was dubbed the Monitor class after the prototype USS Monitor. The Monitor was called by some a “cheesebox on a raft” because of its appearance. Ericsson’s design won the Navy Department competition and was built in a short 100-day time frame.

The ship was 179 feet long with a 41 1/2′ beam and 10 1/2′ draft. The Monitor weighed 987 tons. She was powered by the Ericsson-designed screw propeller and one steam engine also designed by Ericsson. The propeller was recessed into the hull to allow the draft to be very shallow. The ship had a speed of 8 knots per hour. She carried a complement of 49 officers and men.

Ericsson designed a rotating turret that carried 2-11 inch Dahlgren guns. The only problem with the turret was that the momentum required that the guns be fired on the fly. At the short ranges of the early sea battle this did not prove to be a problem. Ericsson designed a better system for stopping the turret on later ships.

The Monitor had very little freeboard being barely above the waterline. The only other projections from the deck besides the turret were the pilothouse, a detachable smokestack and some fittings. The turret had 8 layers of 1 inch plate outside and an additional layer on the inside for sound deadening. The deck was similarly armored.

After the draw at the Battle of Hampton Roads on March 8-9, 1862 Union Navy designers made a number of changes from the lessons that they hadUSS Passaic learned in battle. Within a week after the battle funds for ten new monitor class ironclads were voted by Congress. Ericsson had a number of design changes ready for these new Passaic class ships.

Based on reports from the officers of the USS Monitor Ericsson and his design team incorporated the following improvements:

  • All of the new Passaic class monitors were 200′ long with a 46′ beam for greater stability but retained the shallow draft;
  • The hull was streamlined to allow breaking waves to flow off the deck easier;
  • The pilothouse was moved to the top of the turret for better communication with the gun crew;
  • The turret was redesigned to hold 2-15″ Dahlgren guns but a shortage of them forced the use of 1-15″ gun with an 11″ Dahlgren.

USS Passaic's Gun TurretThe Passaic class monitors had several shortcomings. The deck armor was still thin and they remained vulnerable to plunging fire or any fire from forts. The engines were still inadequate and the larger size didn’t help with their speed. After the unsuccessful attack on Fort Sumter during which several monitors had their turrets jammed by shot, a protective ring was fitted to protect the joint between the turret and the deck.

In July 1862 Ericsson was awarded with a contract for nine more monitors in a new Canonicus class. Five of these ships were commissioned before the end of the war. These vessels were longer and sleeker. They were equipped with improved engines for greater speed. These ships carried 2-15″ Dahlgren smoothbore guns with improved gun carriages. After the Fort Sumter defeat the ships were equipped with the protective ring and the pilothouse was given more armor.

Union Navy authorities tried several bizarre experiments. The steam frigate USS Roanoke was converted to an ironclad in 1862 and had 3 Ericsson turrets mounted on its deck. Each turret was equipped with one smoothbore and one rifled gun. The ship was too top-heavy and the turrets strained the deck timbers. The Roanoke was a costly failure and illustrated that too much of a good thing was sometimes just too much. She spent the rest of the war in Hampton Roads as a harbor defense ship.

The USS Dunderberg was another costly failure. She was originally designed as a two turret ship but the failure of the Roanoke convinced the Chief of Naval Construction John Lenthall whose brainchild this was to change the design to a casemate type. The Dunderberg was a 7,000 ton ram that strained the resources of the Brooklyn Navy Yard. Due to unseasoned timber there were extensive construction delays. The war ended before theUSS Milwaukee ship was completed.

The Milwaukee class monitors were designed for use on rivers and also in coastal waters. A total of four were built in Carondolet, Missouri. They were equipped with one Ericsson turret and one turret designed by James Eads, the builder. They had the shallow draft necessary for rivers. They were equipped with four engines each with its own propeller with a top speed of 9 knots per hour. The Eads turret was fully steam-powered and was considered a great improvement over the Ericsson turret. Of all the monitors built during the war the Eads monitors are considered the best.

In 1862 the Union Navy built a number of twin-turreted monitors. The USS Onondaga was built in Brooklyn and commissioned in March 1864. She was 226′ long with a 50′ beam and her hull was made completely of iron. Each turret was equipped with a 150-pdr Parrot rifle and a 15″ Dahlgren smoothbore. The Onondaga was used in Virginia on the James River. During the Battle of Trent’s Reach on January 24, 1865 her 15 inch shot USS Onondagapenetrated and seriously damaged the CSS Virginia II. 

The four vessels of the Monodnock class were all criticized for their poor hulls. They were all built in Navy yards with wood hulls, armor plate and twin turrets. They all had the same construction delays as the other Navy yard-built ships with only the the USS Monodnock being commissioned before the end of the war.

Ericsson designed a monitor class that was almost twice the size of the original USS Monitor. Named the USS Dictator this behemoth suffered from engine failure and was never used in combat. Her half-sister the USS Puritan which was even bigger was launched in July 1864 but was never completed and languished in the Brooklyn Navy Yard before being scrapped.

The Casco class monitors were originally designed by Ericsson as shallow drift river monitors but were subsequently modified so many times that they were unstable. Additional weight was added to a point where the freeboard was only 3″. The weight of the reinforced turret structure was too heavy for the decking. The turrets were removed and the first three ships were converted to torpedo boats. They were equipped with an 11″ Dahlgren smoothbore in an open mount and a spar torpedo. These three were the only ships of this class that were ever commissioned.

Series Navigation<< Civil War Ironclads: Casemate Type ShipsCivil War Ironclads: Union River Ironclads Part One >>

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