In April 1861 the Navy purchased the 938-ton (burden) screw steamship Phineas Sprague, which had been built at Philadelphia, Pennsylvania, in 1857. Converted to a gunboat and renamed Flag, she was commissioned in late May to take part in the war to subdue the rebellious southern states. USS Flag spent her Civil War career blockading the coasts of South Carolina, Georgia and eastern Florida, participating in the capture or destruction of several would-be blockade runners, among them three steamers. She also was involved in several operations against enemy shore positions, including the occupation of Tybee Island, Georgia, in November 1861, the capture of Fernandina, Florida, in March 1862 and operations against the fortifications protecting Charleston, South Carolina, in 1863. USS Flag was decommissioned in February 1865 and was sold in July 1865. Thereafter, she was the civilian steamship Flag. She was broken up in 1876.