Assigned to Division 21, Atlantic Fleet, "Maddox" departed Boston 3 May 1919 for Trepassey, Newfoundland, en route to the Azores where she became part of a "bridge of ships" assigned to guide US Navy flying boats NC-1 and NC-4 across the ocean on the first transatlantic flight. Returning to Boston on 22 May, the destroyer operated out of there until she sailed for Europe on 26 August 1919. Arriving at Brest, France on 19 September, she soon joined an honor escort for , then bound for Ostend, Belgium, to embark the Belgian King and Queen for the United States. Detached on 25 September, "Maddox" commenced cross-channel service. Until 24 October she escorted ships and carried naval and Army passengers from Dover and Harwich to Boulogne, France, and the Hook of Holland. Departing Harwich on 25 October, the four stacker proceeded through Kiel Canal to visit various Baltic ports.