"Saturn" was placed in service on 2 December 1903 on a merchant basis and attached to the Pacific Squadron the same day. She operated on the United States west coast, from San Diego, California to Elaine, Washington, into 1908. She made one voyage to Kiska and Dutch Harbor, Alaska, during mid-1904, and another to Honolulu and Midway Island in January 1906, carrying coal for shore facilities. She also cruised in Mexican waters during January, April, July, and August 1907, supplying ships of the fleet.