USS Shamrock was a large (974 ton) seaworthy steamer with powerful guns, acquired by the Union Navy during the American Civil War.

During the war, she participated in the operation of placing a spar torpedo into the ironclad CSS Albemarle, allowing Shamrock to sail on with the Union fleet to attack and capture Plymouth, North Carolina.

On the 20th, Shamrock reached Hatteras Inlet where orders awaited her to enter Albemarle Sound and take station off the mouth of the Roanoke River to guard against the reappearance of the formidable Rebel ram.

For the next four months, Shamrock's operations concentrated on protecting Union shipping from Albemarle, which was undergoing repairs up the Roanoke River.

Late in October, Shamrock served as the mother ship of the steam launch which Lt. William Barker Cushing had brought to the sounds from New York City to attack Albemarle.

The small cutter accompanied them, the crew of which had the task of preventing the Confederate sentries stationed on a schooner anchored to the wreck of Southfield.

Commander Alexander F. Worley, who had been appointed as her captain about a month earlier, salvaged her guns and shells and used them to defend Plymouth against subsequent Union attack—futilely, as it transpired.

Albemarle and the launch quickly sank and, for the first time since spring, Union naval forces enjoyed undisputed control of the North Carolina sounds.

Shamrock, lashed to tug USS Bazely, led a fleet through the winding channels of Middle River on 30 October and the next day engaged the town's batteries and rifle pits from close range.