Assigned to the 5th Naval District at Norfolk, Robert L. Barnes departed New York 12 March 1919 for Hampton Roads.

The ship remained inactive at Norfolk and was undergoing overhaul 4 September 1919 when she was assigned to the Naval Overseas Transportation Service.

The ship remained at Guam through the interwar decades, departing only in 1920, 1921, 1922, 1923, 1930, and 1934 under tow for Cavite Naval Base, Philippine Islands, for overhaul.

During Japanese air attacks on the island, 8 December 1941, the oiler was bombed and strafed at her mooring, causing damage topside and starting dangerous leaks.

Still afloat when the Japanese invasion force landed on Guam, Robert L. Barnes was abandoned and fell into enemy hands 10 December 1941.