The U.S. Navy inspected her in the 3rd Naval District in 1917 for possible World War I service, and acquired her from Munson on 28 June 1918 for use as a cargo ship.

Assigned to the Naval Overseas Transportation Service, Munsomo took on a cargo of United States Army supplies and departed New York City on 9 August 1918 to cross the Atlantic in a convoy, bound for France.

After discharging her cargo she moved on to Le Verdon-sur-Mer, France, then returned to the United States, arriving at Baltimore on 25 September 1918.

Munsomo next made a run to Antilla, Cuba, carrying general supplies and returned to the United States with a cargo of sugar, arriving at New York City.

Munsomo was decommissioned on 4 February 1919 and transferred to the United States Shipping Board the same day for simultaneous return to Munson Steamship Line.