[3][4] The U.S. Navy commandeered her on 21 March 1918 for World War I service, assigned her the registry Identification Number (Id.

1298, outfitted her for service as a troop transport at Mare Island Navy Yard at Vallejo, California, and commissioned her as USS Harvard (ID-1298) on 9 April 1918.

On 27 July 1918, Charles reported at Southampton, England, for duty as a ferry for troops crossing the English Channel.

She made about 60 voyages between Southampton and Le Havre or Boulogne, France, carrying troops of all nationalities bound for action at the front during the war or for occupation duty after it ended, until 5 May 1919.

Her ferrying duties completed, Charles embarked passengers at Rotterdam in the Netherlands and at Brest for transportation to the United States, and on 15 June 1919, arrived at New York City.