An original civil war photo, showing the yankee ironclad Onondaga at anchor in the James River below Richmond VA in 1865. Many people have seen photos or paintings of the first yankee ironclad warship, the USS Monitor, which fought the famous duel with the first Confederate ironclad, the CSS Virginia, also called the Merrimack. So, to most people, the yankee ironclads had only a single turret. But in 1864 the yanks came out with twin-turreted ironclads. Each turret held two heavy-caliber cannons, including a 15-inch caliber monster. The Confederate Navy had nothing which could withstand a direct hit from a 15-inch Solid-Shot cannonball (weighing about 454 pounds).
Of additional interest... this unique "off-duty" photo shows the sailors' laundry hung out to dry on ropes strung from the ironclad's turrets to its smokestack.
Click on the image, and then click again for super-enlargement to see small details better.