The United States Shipping Board acquired her from Munson for World War I service early in 1918 and transferred her to the U.S. Navy on 15 April 1918.

Assigned to the Naval Overseas Transportation Service, Walter D. Munson loaded United States Army supplies at New York City and put to sea on 25 April 1918 with a convoy bound for France.

She concluded her first Atlantic crossing in Navy service at Brest, France, on 10 May 1918 and moved on to Gironde on 13 May 1918, in which port she unloaded her cargo and took on ballast for the return voyage.

After completing voyage repairs and loading another U.S. Army cargo, Walter D. Munson departed in an eastbound convoy for Europe on 18 June 1918 and arrived at Brest on 4 July 1918.

During a week at New York, Walter D. Munson completed another series of voyage repairs and loaded her fourth Europe-bound cargo.

She stood out of Nantes on 6 December 1918 and headed for Brest, where she loaded a cargo of steel rails for return to the United States.