The Neosho-class monitors were a pair of ironclad river monitors laid down in mid-1862 for the United States Navy during the American Civil War. After completion in mid-1863, both ships spent time patrolling the Mississippi River against Confederate raids and ambushes as part of Rear Admiral David Porter's Mississippi Squadron. Both ships participated in the Red River Campaign in March–May 1864, although Osage supported the capture of Fort DeRussy in March and participated in the Battle of Blair's Landing in April. Osage was grounded on a sandbar for six months after the end of the campaign while Neosho resumed her patrols on the Mississippi. The latter ship supported the Union Army's operations on the Cumberland River and provided fire support during the Battle of Nashville in December.

The Mississippi River Squadron was the Union brown-water naval squadron that operated on the western rivers during the American Civil War. It was initially created as a part of the Union Army, although it was commanded by naval officers, and was then known as the Western Gunboat Flotilla and sometimes as the Mississippi Flotilla. It received its final designation when it was transferred to the Union Navy at the beginning of October 1862.