She was sponsored by Mrs. M. H. Simons, great-granddaughter of Captain Downes and outfitted for service at Philadelphia Navy Yard.

Downes conducted her shakedown off New York and in Chesapeake Bay, and then returned to Philadelphia Navy Yard, where she was placed in ordinary from 4 October 1915 – 26 May 1917 for the construction and installation of new machinery by the contractor.

Fitted out for distant service, she sailed from New York on 18 October 1917 for Devonport, England, arriving on 7 November.

She patrolled against submarines off the Irish coast, making numerous attacks with no sure results and with other destroyers aided distressed ships.

The day after Christmas she sailed for the United States, arriving at Norfolk, Virginia on 18 January 1919.