USS Cairo /ˈkeɪroʊ/ is the lead ship of the City-class casemate ironclads built at the beginning of the American Civil War to serve as river gunboats.

In June 1862, she captured the Confederate garrison of Fort Pillow on the Mississippi River, enabling Union forces to occupy Memphis.

Cairo was built by James Eads and Co., Mound City, Illinois, in 1861, under contract to the United States Department of War.

She was commissioned as part of the Union Army's Western Gunboat Flotilla,[1] which had US Navy Lieutenant James M. Prichett in command.

An engagement with Confederate gunboats at Plum Point Bend on 11 May, marked a series of blockading and bombardment activities which culminated into the abandonment of the fort by its defenders on 4 June.

Impacted in mud, Cairo became a time capsule in which her unique, historical artifacts were preserved against corrosion and biological degradation.

Studying Civil War maps, Edwin C. Bearss of Vicksburg National Military Park set out to search for the lost ship using a simple magnetic compass.

Sections of the hull were braced internally and a sprinkler system was operated continually to keep the white oak structural timbers from warping and checking.

Delays in funding the project halted progress until June 1977, when the vessel was transported to the park and partially reconstructed on a concrete foundation near the Vicksburg National Cemetery.

The recovery of artifacts from Cairo revealed a treasure trove of weapons, ammunition, naval stores, and personal gear of the sailors who served on board.