early 1917, Parker joined the fleet at Yorktown, Virginia, in March, immediately prior to the American entry into World War I. World War I After the U.S. entered World War I on 6 April 1917, Parker was selected for overseas duty. She sailed on 17 June as an escort for the fourth group of the first American convoy, which carried units of the American Expeditionary Force. The convoy consisted of United States Army transports , , , and ; U.S. Navy transport ; and oiler . The escorts — in addition to Parker — were the cruisers , and destroyers , , and . The group departed from New York for Brest, France, steaming at an pace. A thwarted submarine attack on the first convoy group, and reports of heavy submarine activity off of Brest, resulted in a change in the convoy's destination to Saint-Nazaire where the convoy arrived 2 July. From St. Nazaire, Parker steamed to Queenstown, Ireland, joining the U.S. Naval Forces patrolling the Irish Coast. There she escorted convoys safely through the war zone, and assisted vessels in distress. From July–November 1918, Parker was attached to the base at Plymouth, England, and operated with U.S. submarine chasers. Parker made contact with German submarines on several occasions during the war. She was credited with probably seriously damaging an enemy submarine on 3 August 1917. On 26 February 1918, Parker assisted in rescuing nine survivors of British hospital ship , which had been torpedoed by German submarine . The men of Parker were commended by the British Parliament, the Admiralty, and the U.S. naval authorities. On 1 November, Parker sailed from Plymouth for Gibraltar but returned to Plymouth at the end of the war. Postwar After returning to Plymouth after the Armistice was signed, Parker carried mail and passengers between Plymouth and Brest. She made a cruise to German ports in early 1919 to implement the terms of the armistice, before steaming to the Baltic Sea to assist members and vessels of the American Relief Administration. Parker sailed for New York on 20 July 1919 and, upon arrival, was assigned to Destroyer Squadron 1, Atlantic Fleet. The destroyer was based out of Norfolk, Virginia from 1919-mid-1921. In July 1920, Parker was operating in the Mediterranean when she played a role in the search for an American missionary couple, Paul Nilson and Harriet Fisher Nilson, thought abducted by Turkish Nationalists.