USS Shamrock, a 974-ton Sassacus class "Double-Ender" side-wheel gunboat, was built at the New York Navy Yard, Brooklyn, N.Y. Commissioned in June 1864, she was immediately sent to the North Carolina Sounds, where she remained through the rest of the Civil War. Shamrock served as "mother ship" for Picket Boat Number One at the time of Lieutenant William B. Cushing's successful spar torpedo attack on the the Confederate ironclad Albemarle on 27-28 October 1864, and provided some of Cushing's crew for that daring venture. A few days later, on 31 October 1864, Shamrock was flagship of a force of U.S. Navy gunboats that captured Plymouth, N.C. She continued her operations in the Sounds area until the summer of 1865.

Shamrock was decommissioned in August 1865, but recommissioned the following October and was sent to the West Indies. During 1866-68, she served in European waters. USS Shamrock decommissioned for the last time in August 1868 and was sold the following month.