USS Sangamon was a Passaic-class ironclad monitor constructed for the Union Navy during the second year of the American Civil War where she operated in the waterways of the Confederate States of America.

The monitor was assigned to the North Atlantic Blockading Squadron and soon began efficient but unspectacular operations in Hampton Roads, Virginia and in the many roughly parallel rivers which empty into Chesapeake Bay.

Sangamon was one of the vital ships of the Navy which guaranteed the Army control of the waters which border and penetrate the bitterly contested land which separated Washington, D.C., and Richmond, Virginia.

After Union blockade duty off Charleston, South Carolina, she returned to Hampton Roads in the summer to support General Ulysses S. Grant's drive on Richmond, Virginia.

She conducted reconnaissance expeditions up the river to obtain information, and often dueled Confederate forces hidden along the banks.