Coos Bay cleared San Diego 22 July 1943 for Pearl Harbor, Espiritu Santo and Cavutu, where she established a seadrome for Patrol Squadron 71 from 13 October until 23 November. She was based successively at Tulagi, at Blanche Harbor in the Treasuries, and at Green Island until 16 June. After carrying men and equipment of Fleet Air Wing 1 from New Georgia to Espiritu Santo, Coos Bay sailed 21 August for Guadalcanal, where she unloaded aviation equipment. From 8 September to 9 December she served at Saipan as station tender, then returned to San Pedro, Calif., for an overhaul.
The tender returned to Pearl Harbor 17 March, and 4 days later sailed for Ulithi. During her passage, she collided with a merchant vessel which took her in tow for emergency repairs at Eniwetok, then Coos Bay proceeded to San Pedro, Calif., for overhaul. Returning to Pearl Harbor, Coos Bay remained there until 1 September, and then sailed for Ominato Ko, Honshu, Japan, arriving 13 September for station tender duty until 2 December, when she proceeded to Orange, Tex., arriving 11 January 1946 for inactivation. Coos Bay was placed out of commission in reserve 30 April 1946, and was lent to the U.S. Coast Guard 5 January 1949.
Coos Bay received two battle stars for World War II service.