USS C.P. Williams, a 210-ton mortar schooner, was built in 1851 at Hoboken, New Jersey, for commercial use. She was purchased by the Navy in September 1861, outfitted for combat employment and commissioned in January 1862. Assigned to the Mortar Flotilla then preparing for operations on the lower Mississippi River, C.P. Williams took part in the bombardments of Forts Jackson and St. Philip in April 1862 and of Vicksburg, Mississippi, in June and July of that year. She also carried out routine patrol duties in the vicinity before returning to the Atlantic coast for repairs in mid-summer 1862.

C.P. Williams joined the South Atlantic Blockading Squadron in November 1862 and served for the rest of the Civil War along the coasts of South Carolina and Georgia. Among her activities were bombardments of Fort McAllister, Georgia, in November 1862 and January-March 1863, an engagement with Confederate batteries on the Stono River, S.C., in December 1863 and operations up the Stono and Folly Rivers in February 1865. USS C.P. Williams was sent north in June 1865 and decommissioned. She was sold in August 1865 and later became the merchant vessel Sarah Purves.