Following sea trails in Puget Sound, N-3, with sister ships N-1 (SS-53) and N-2 (SS-54), departed the Navy Yard on 21 November 1917. The three submarines arrived at New London, Connecticut, on 7 February 1918. From here, N-3 patrolled along the New England coast and off Long Island. On 23 July, a British steamer mistook N-3 as a German U-boat and fired on her at a range of only 50 yards. Although hit by a six-inch shell, the submarine suffered only slight damage and after repairs at sea, was able to proceed to New York Navy Yard under her own power. Following permanent repairs, N-3 returned to the Submarine School, New London for patrol and training duty through 1920.