Unalaska (ŭn'əlăs`kə, o͞o'nə–), rugged island, 30 mi (48 km) long, off SW Alaska, one of the largest Aleutian Islands. Visited (c.1759) by Russian explorers, the island was a center of Russian fur trade until it was superseded by Kodiak. Spruces planted on Unalaska by the Russians remain among the few trees in the Aleutians. The main city on the island is Unalaska. Dutch Harbor, located on Amaknak Island, is now a section of the city and the most important commercial fishing port in the United States. Naval and army bases were established at Unalaska in the early 1940s and decommissioned in 1947.