USS Sassacus was built at the Portsmouth Navy Yard, Kittery, Maine, as the first of a class of twenty-eight 974-ton "Double-Ender" side-wheel steam gunboats. Commissioned in October 1863, she spent several months undergoing repairs and then joined the blockade off Wilmington, North Carolina. In February 1864, Sassacus was involved in the destruction of two blockade runners, one after a long chase. She began operations in the North Carolina Sounds in April 1864, and on 5 May closely engaged the Confederate ironclad CSS Albemarle. During this action, Sassacus was badly damaged when she rammed the enemy ironclad, which escaped essentially unhurt. Despite her damages, she remained on duty in North Carolina and Virginia waters until September 1864, when she could finally be released for refit.

Sassacus returned to war service in November 1864 and took part in the two assaults on Fort Fisher, N.C., in December and January. She then operated on the rivers leading to Wilmington, N.C., and Richmond, Virginia, during the remaining months of the Civil War. Sassacus decommissioned in May 1865 and was sold in August 1868.