Shawmut served the Union Navy primarily as a gunboat with howitzers for bombardment, and various other rifles and cannon for use at sea in apprehending blockade runners attempting to “run” the Union blockade of the Confederate States of America.
Shawmut—a screw gunboat begun on 2 February 1863 by the Portsmouth Navy Yard (Kittery, Maine) -- was launched on 17 April 1863; sponsored by Miss Lucy Hall; departed Portsmouth, New Hampshire, on 20 October 1863; was towed to New York City where her engine and machinery were installed by the South Brooklyn Works; was delivered to the Union Navy on 16 October 1864; and commissioned at the New York Navy Yard on 1 November 1864, Lt. Comdr. George U. Morris in command.
Two days later, Shawmut got underway to search for Confederate Navy commerce raider, CSS Tallahassee (renamed Olustee), which had recently preyed upon Northern shipping off the Delaware capes. After cruising in Nova Scotian waters without seeing or hearing of her quarry, Shawmut returned to the Portsmouth Navy Yard on the 20th.
On 9 January 1865, the gunboat was ordered to proceed to Wilmington, North Carolina, to join the North Atlantic Blockading Squadron. She participated in the attack on and capture of Fort Anderson, North Carolina, from 18 to 20 February. On the latter day, a boat from Shawmut was destroyed by a torpedo (the Civil War term for a mine) as it swept waters in the area.