USS Saint Louis, a 512-ton Cairo class ironclad river gunboat, was built at Saint Louis, Missouri, for the U.S. Army's Western Gunboat Flotilla. Commissioned in January 1862, she participated in battles at Forts Henry and Donelson, Tennessee, and Columbus, Kentucky, during the month of February. Saint Louis was badly hit and disabled by Confederate cannon fire during the action at Fort Donelson. From March into May 1862, she was involved in operations to capture enemy Mississippi River fortifications at Island Number Ten and Fort Pillow, then was present during actions off Memphis, Tennessee, and in the White River, Arkansas, in June.

In September 1862, Saint Louis was renamed Baron de Kalb as part of the process of transferring the Western Gunboat Flotilla to the Navy. During November and December 1862, she took part in operations on the Yazoo River. Early in the new year, Baron de Kalb participated in the capture of Fort Hindman, Arkansas, then returned to the Yazoo for further operations. On 13 July 1863, during an expedition on that river, she was sunk by a Confederate mine.