The largest rifled gun used during the war by the U.S. Navy was the 8-inch Parrott. For the Navy, these were primarily anti-ironclad weapons, with a secondary role in reduction of coastal fortifications. Naturally, the 8-inch rifles found use on some of the powerful Federal ironclads.
Among the early ironclads, the USS New Ironsides featured 8-inch Parrotts as broadside weapons. One of the big Parrotts complemented the seven 11-inch Dahlgrens on each side. Although the New Ironsides could run closer to shore than some of the unarmored heavy steam frigates, her draft was still too much for operations in the rivers and inlets. However, unlike contemporary monitors, the “damned iron box” with a high freeboard was rather useful on the high seas. Her wartime service included bombardments of Forts Sumter and Fisher, and certainly deserves a more lengthy study than space permits here.
In the days after the USS Monitor and CSS Virginia duel, the US Navy continued a crash program to obtain more ironclad vessels by way of conversion or new construction. Among the conversions was the USS Roanoke, a steam frigate and sister-ship of the USS Merrimack (which the Confederates had converted to the Virginia).
In April 1862, the Brooklyn Navy Yard razed the ship, cutting down to the gun deck. Novelty Iron Works provided iron plating. Three of John Ericsson‘s turrets, similar to that used on the Monitor, supported the ship’s armament which included two 15-inch smoothbores, two 11-inch Dahlgren smoothbores, and two 8-inch Parrotts.
The forward (right in this view) turret bore one of the 15-inch smoothbore and one of the 8-inch Parrotts. The center turret had 15-inch and 11-inch smoothbores. And the aft turret had the remaining 11-inch Dahlgren and 8-inch Parrott. A rather powerful broadside. The armament layout anticipated later big-gun turreted battleships by a few decades. But the Roanoke was more of an albatross in service. Too deep to navigate up the James River or into southern harbors, and not stable enough on the high seas, the Roanoke served mainly as a flagship.
Another a multi-turret monitor, the USS Onondaga also received 8-in Parrotts. Each of the Onondaga‘s two turrets mounted a 15-inch smoothbore and an 8-inch Parrott.
However in the Battle of Trent’s Reach, on January 24, 1865, it was the large Dahlgrens, not the Parrotts, which smashed the CSS Virginia II. After the war the Navy returned Onondaga to her builder, G.W. Quintard, who then sold her to France. Not clear is if the ship passed into French hands with the US guns. In later years she used breechloading guns of French design. The Onondaga served as a coastal defense ship until the early 1900s.
The monitor USS Patapsco mounted an 8-inch Parrott during operations off Charleston. The only other monitors to use the 8-inch Parrotts were some of the light-draft, and largely unsuccessful, Casco-class. John Ericsson designed the class to operate in shallow waters – intended to only draw 6 feet. After design modifications, engineering issues, and contention among Navy brass, the Casco project devolved into a foul-up of the first magnitude with corresponding cost overruns. With weights exceeding original designs, builders completed some of the Casco-class without turrets. Most of the class required extensive refits before commissioning.
The USS Casco and USS Chimo saw active service during the war. Two others, the USS Naubuc and USS Tunxis, received commissions before the end of the war. The Navy accepted the remaining sixteen after the war, but laid them up in reserve.
Designed for two 11-inch Dahlgrens, most of the class only received one, if that. However, some sources indicate the Tunxis, which retained its turret, carried an 8-inch Parrott alongside her 11-inch gun. The Chimo, without turret, carried a single 8-inch Parrott for at least part of her service life.
Overall only a handful of ironclads received 8-inch Parrotts. Their service record is mixed at best. While the New Ironsides might be considered one of the best armored ships of the war, and the Onondaga at least a limited success, the Roanoke and Cascos were disappointments. The navy preferred large caliber smoothbore guns for anti-ship work instead of the Parrotts. So the Passaic and Canonicus classes, the more numerous monitors of the war, received smoothbores.
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Olmstead, Edwin, Wayne E. Stark, and Spencer C. Tucker. The Big Guns: Civil War Siege, Seacoast and Naval Cannon. Alexandria Bay, NY: Museum Restoration Service, 1997.
Silverstone, Paul H. Warships of the Civil War Navies. Annapolis, MD: Naval Institute Press, 1989.
Tucker, Spencer. Arming the Fleet: U.S. Navy Ordnance in the Muzzle-Loading Era. Annapolis, Maryland: Naval Institute Press, 1989.