Group of the Aleutian Islands, southwestern Alaska, U.S. Lying between the Pacific Ocean and the Bering Sea, the islands extend east to west about 270 mi (430 km) between the Fox and Rat island groups. They were strategically important in World War II, when U.S. military bases were developed, especially on Adak Island. Other islands in the group include Atka, Tanaga, and Kanaga.