USS Onondaga was an ironclad river monitor built for the Union Navy during the American Civil War. Commissioned in 1864, the ship spent her entire active career with the James River Flotilla covering the water approaches to the Confederate States capital of Richmond, Virginia, although her only notable engagement was the Battle of Trent's Reach. After the war, she was purchased by France where she served as a coastal defense ship in the French Navy (). Onondaga saw little active service with the French, spending most of the next four decades in reserve, although she was mobilized during the Franco-Prussian War of 1870–1871. The monitor became a guard ship in 1898, but she was stricken from the naval register and sold for scrap in 1904; the ship was demolished in 1905. Description Onondaga had an overall length of and a beam of . She was overweight and her draft of was almost a foot deeper than intended. The ship had a depth of hold of , a tonnage of 1,250 tons burthen and displaced . Her crew consisted of 130 officers and enlisted men. Onondaga was powered by a pair of two-cylinder horizontal back-acting steam engines, built by the Morgan Iron Works, each driving one propeller using steam generated by four vertical water-tube boilers. The engines had a combined rating of that gave the ship a speed of . She carried of coal which gave her a range of . The propellers were protected from underwater obstacles by iron rings. The monitor's main battery consisted of a pair of smoothbore, muzzle-loading, Dahlgren guns and another pair of 150-pounder () Parrott rifles. One of each type was mounted in the two twin-gun turrets. Her pilothouse was built on the roof of the forward turret. Steam power to rotate each turret was provided by a two-cylinder donkey engine. The nine-caliber Dahlgren guns weighed . They could fire a shell up to a range of at an elevation of +5°. The Parrott rifles were 17 calibers long and weighed . Their projectiles had a range of at the same elevation. As designed the exposed area of the hull was protected by wrought-iron plates, but John Ericsson, designer of the , suggested that the side armor be reinforced with additional wood inside the armor belt in April 1863. As most of the armor had already been mounted by this time, the shipyard simply added