The USS Cairo was a city-class ironclad built in 1861 at Mound City, Illinois, by James Eads and company, paid for by the War Department, crewed by the Navy and commanded by Lieutenant James M. Pritchett. Its casemate carried two and a half inches of iron plate, with three and a half inches of railroad iron on the forward sides, and its guns ranged from 8-inch Dahlgrens to old 32-pounders and 42-pounder rifles cut from smoothbore barrels. In 1862 the Cairo took part in the occupations of Clarksville and Nashville, operations against Fort Pillow, Plum Point Bend and the June 6 Battle of Memphis, and passed to the Navy on October 1.

On December 12, 1862, while clearing mines on the Yazoo River ahead of an attack on Haynes Bluff, the Cairo passed over a powder charge in a demijohn wired to a galvanic battery on shore. Confederates closed the circuit, and the ship sank in 12 minutes without a single death among its 251 men. The river’s oxygen-free silt preserved it until 1956, when Edwin C. Bearss, Don Jacks and Warren Grabau found it using Civil War maps and a pocket compass. In 1964 lifting cables sliced through the waterlogged hull, forcing the team to cut the ship into three sections, which were taken to the Ingalls Shipyard in Pascagoula and kept wet by sprinklers during conservation before reaching Vicksburg National Military Park in 1977.

• The 12-pounder howitzers aboard were there to repel boarding parties in close river fighting.
• At Memphis, seven Union vessels faced eight Confederate gunboats, and only one Confederate boat escaped.
• The Cairo is described as the first ship in history sunk by a remotely detonated mine.
• The pilothouse and an 8-inch cannon were raised by 1960, and the remains were listed on the National Register of Historic Places in 1971.
• Artifacts on display include a preserved sailor’s rope knife, and the Cairo is one of four surviving Civil War ironclads.