After being mustered in, the 3rd New Hampshire left for Long Island, New York, encamping at Camp Winfield Scott at Hempstead Plains. From here, they went to Washington, D.C. and Annapolis, Maryland before arriving at Hilton Head, South Carolina, as part of the forces used to establish Federal footholds on the South's Atlantic Coast. Except for minor skirmishes with Confederate pickets, they did not see action until June 16, 1862, where it participated in the Battle of Secessionville. The 3rd entered battle with 26 officers and 597 men and suffered 104 casualties—27 of them killed or mortally wounded.