After shakedown, Moose departed Balboa, Panama Canal Zone, on 15 March 1944 for the South Pacific. Upon arrival New Caledonia in November, she reported to Commander, Southern Pacific, for duty as a mobile floating oil storage ship. From May to August 1945 Moose served as a fuel supply ship supporting the effort to end the war against Japan, calling at Ulithi, the Palau Islands, Leyte Gulf, Okinawa, and Kerama Retto, discharging her one-millionth barrel of fuel at Buckner Bay, Okinawa, on 21 August.
With the end of the war in the Pacific, Moose reported to the Atlantic Fleet at Norfolk, Virginia, on 4 February 1946. She decommissioned there 19 April 1946, was returned to the War Shipping Administration on 27 April 1946, and stricken from the Naval Vessel Register on 8 May 1946. She entered the National Reserve Defense Fleet as Mason L. Weems. In 1948 she was sold to Tramp Shipping & Oil Transportation Corporation for service as Yankee Pioneer. Resold to Weyerhaeuser Steamship Company in 1951, the ship was renamed Y. L. McCormick.