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

The Pook Turtles, or City-class gunboats to use their semi-official name, were war vessels intended for service on the Mississippi River during the American Civil War. They were also sometimes referred to as "Eads gunboats." The labels are applied to seven vessels of uniform design built from the keel up in Carondelet, Missouri shipyards owned by James Buchanan Eads. Eads was a wealthy St. Louis industrialist who risked his fortune in support of the Union.