"Casco" returned to duty in the Aleutian Islands in March 1943, operating at Constantine Harbor, Amchitka, as tender to Fleet Air Wing Four (FAW-4). In May 1943 she moved to Attu, to care for the seaplanes conducting antisubmarine patrol and search missions in support of the United States Army's invasion of Attu, guarding against further Japanese reinforcement or penetration of the Aleutians. "Casco"s service in these waters where weather was often as formidable an enemy as the Japanese ended in November 1943, when she left for overhaul at Puget Sound Navy Yard. During one of her stays in the Aleutians, an OS2U Kingfisher from the Casco was borrowed by Colonel William O. Eareckson for use as a forward air control aircraft, which personally flew on numerous missions.