Although completed as a coastal operations monitor, the twin turreted ship Onondaga spent her entire active career in US Service patrolling the inland waterways of the Confederacy, and the vast majority of this time was spent on the James. She was often the only available armored ship on call to respond to break out and attack attempts by the James River Squadron, and was the principle Union ironclad in the 1864 and 1865 Battles of Trent's Reach. During the most famous of these in February 1865, a long range barrage from her turrets penetrated the pilot house of CSS Virginia II, causing her to deviate off course and turn abruptly, which gave the signal to the rest of the Squadron that a retreat had been decided upon, and essentially saved the day. Ironically, Onondaga's commanding officer was court-martialed for "failure to act aggressively" when he failed to pursue the James River Squadron as it sailed back up the river to Richmond.
Onondaga was an unusual design. She had two turrets on a boat like hill, the forward of which was equipped with a very large pilot house (it has been argued that this may have been the largest pilot house to be installed on any monitor type vessel in Union service during the war). She had a reinforced armored deck with extra plating over key sections of her interior (these are the raised iron plates you see on the surface of her hull.) She was said to be very well ventilated for a ship of her type, and her ventilators were both taller than normal and slightly flat, as opposed to the standard "pipe shaped" ventilator. In addition, she had a shallow draft but was remarkably seaworthy, a feat she proved after the war when sold to the French. She sailed under her own power across the Atlantic and was given a hero's welcome in France. So impressed were the French with the war record that they accorded her a rare honor: they commissioned her with the same name, and she remained in French service for three decades, rendering valuable service. Her scrapping was widely protested by the French population, many of whom believed she should have been preserved as a museum ship.
Onondaga has printed well in WSF, though once again, I do recommend BSF for the extra dollar, as it's polished before delivery and makes for a better, more paintable service.
Historically, Onondaga was primarily black; her turret parapets and pilot house were white. It would be very typical for this black to quickly weather to a charcoal grey color.