(Sidewheel Steamer: tonnage 974; length 205'; beam 35'; depth of hold 12'; draft 8'10"; speed 13 knots; complement 160; armament 2 100-pounder Parrott rifles, 4 9-inch Dahlgren smoothbores, 2 20-pounder Parrott rifles, 2 24-pounder howitzers, 1 heavy 12-pounder smoothbore)
Shamrock – a double-ended side wheel gunboat built at the New York Navy Yard – was launched on St. Patrick's Day, 17 March 1863; sponsored by. Miss Sallie Bryant, daughter of William Cullen Bryant, editor-in-chief of the New York Evening Post; and commissioned on 13 June 1864, Comdr. William H. Macomb in command.
The next day, Shamrock was ordered to proceed directly to the sounds of North Carolina for duty in that area as part of the North Atlantic Blockading Squadron. At that time, Union naval forces in the sounds were threatened by the Confederate ironclad ram Albemarle, which in April had sunk Union side wheel steamer, Southfield, and had enabled Southern forces to recapture Plymouth, N.C.
On 20 June 1864, 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, that lay undergoing repairs up the Roanoke.
Late in October, she served as the mother ship for the steam launch that Lt. William B. Cushing had brought to the sounds from New York City to attack Albemarle. On the night of 27 and 28 October, the launch - partly manned by volunteers from Shamrock and towing Shamrock's cutter - ascended the Roanoke and exploded a spar torpedo against the ram's port quarter. Just before the explosion, Cushing ordered the cutter to cast off. Albermarle and the launch sank quickly and, for the first time since spring, Union naval forces enjoyed undisputed control of the North Carolina sounds.
When the fortunate Cushing made his way back and reported his success, Comdr. Macomb - the senior naval officer in the area - promptly took advantage of his new ascendency and attacked Plymouth. Shamrock, lashed to tug 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. Commodore Hull suffered heavy damage in the violent battle that ensued. After the Union bombardment detonated a large magazine, the Confederate defenders evacuated the fortress. Soon a landing party raised the Stars and Stripes over Plymouth.
Through the ensuing winter, Comdr. Macomb, in Shamrock, directed operations in the sounds, assuring the Union control of these strategic waters as General Ulysses S. Grant relentlessly tightened his grip on Richmond, and General William T. Sherman pushed his army northward from Georgia through the Carolinas. On 20 March 1865, Macomb reported the raising of Albemarle.
Shamrock remained in the sounds directing affairs afloat in the area for several months after the Confederate collapse. In mid-summer, she returned north and was decommissioned at the Philadelphia Navy Yard on 15 August 1865.
Recommissioned on 17 October 1865, Shamrock next served in the Caribbean and was one of the nine ships comprising the West Indies Squadron that was reestablished on 2 December. The following year, the double ender crossed the Atlantic for service in European waters. She returned to the United States in July 1868 and was decommissioned at the Philadelphia Navy Yard on 10 August. Shamrock was sold on 1 September 1868 to Mr. E. Stannard of Westbrook, Conn.
Shamrock - a side wheel steamer purchased by the Navy on 16 July 1864 -- was renamed Isonomia (q.v.) shortly thereafter.