Assigned to the Naval Transportation Service, Vega served the Navy from Atlantic to Pacific on cargo runs which included calls at both east- and west-coast ports, as well as visits to the Far East and the Caribbean.

In successive summers from 1925 to 1928, the cargo vessel operated between Seattle, Washington, and Alaskan ports, carrying supplies and stores to naval radio stations at St. Paul and Dutch Harbor.

In addition, Vega and sister ship Sirius (AK-15) carried general freight, heavy guns, and ordnance parts in support of Marine peacekeeping activities in Nicaragua.

When Japanese aircraft swept over Oahu, Vega went to general quarters, opening fire with her anti-aircraft guns, as civilian stevedores continued the arduous job of unloading her dangerous cargo.

On one run, Vega delivered a cargo of naval stores and ammunition, as well as some 20 mm anti-aircraft guns for the garrison at Dutch Harbor — only a few days before the devastating bombardment of that base by a Japanese light carrier strike force in early June 1942.

On 23 October 1944, Vega commenced loading empty brass powder cans at Ulithi in the Carolines, while her embarked "Seabee" battalion — the 1044th — assembled self-propelled barges brought out in SS Claremont.

Subsequently, the cargo vessel sailed for Eniwetok where she took on board another load of brass casings, heading for Pearl Harbor on 30 December, en route to the west coast.