Joining the Atlantic Fleet, Monaghan took part in fleet readiness training and operations, which prepared the US Navy to enter action immediately when its country joined the Allies in World War I. Monaghan’s first war service was on patrol along the Atlantic coast; she then escorted troop convoys through the dangerous mid-ocean section of their crossings. From November 1917 until the Armistice a year later, Monaghan made antisubmarine patrols against the U-boat menace in European waters.
Monaghan was decommissioned at Philadelphia on 4 November 1919 and, while inactive, was redesignated DD 32 during the assignment of alphanumeric hull numbers on 17 July 1920.
Transferred to the US Coast Guard on 7 June 1924, Monaghan was commissioned at Philadelphia on 30 June 1925. Ordered to New London, Connecticut on 22 May 1926, she arrived at her destination on 10 July. She operated off the eastern seaboard of the United States between New London and St. Petersburg, Florida, punctuating that duty with visits to Charleston, South Carolina until transferred to the Boston, Massachussetts-based Division 3 on 1 June 1930. Monaghan ultimately returned to Philadelphia on 1 November 1930, and was decommissioned there on 29 January 1931. She was returned to the Navy on 8 May 1931.
The Navy dropped the name Monaghan on 1 July 1933 so that it might be assigned to a new construction destroyer. DD 32, as the ship was subsequently known, was stricken from the Naval Vessel Register on 5 July 1934. She was then sold to Michael Flynn of Brooklyn, New York on 22 August 1934 for scrapping in accordance with the London Treaty limiting naval armament.