Sirius was assigned to the Naval Transportation Service carrying cargo and passengers in support of fleet units and bases. For many years, Sirius operated along the coasts of the United States. She operated on the east coast as far north as Boston, Massachusetts, and reached many ports in the Caribbean. Upon moving to the west coast, she operated from San Diego, California, to Bremerton, Washington. During 1929, 1930, and 1932, Sirius made numerous trips to and from Alaska with sealskins as her principal cargo. In 1934, she was attached to the Aleutian Island Survey Expedition and made cruises to many of the islands of Alaska, charting their waters as she went.