uninhabited group of the Aleutian Islands, southwestern Alaska, U.S. They extend about 110 miles (175 km) southeast of the Near Islands and west of the Andreanof Islands. The largest of the islands are Amchitka, Kiska, and Semisopochnoi. Separated from the Andreanof Islands by Amchitka Pass, one of the main navigational lines through the Aleutian Islands, the Rat Islands are part of the extensive Alaska Maritime National Wildlife Refuge. Kiska Island was occupied by the Japanese during World War II. In 1965, 1969, and 1971, the U.S. Department of Defense and the Atomic Energy Commission conducted underground nuclear tests on Amchitka Island. Semisopochnoi Volcano, which rises to 4,005 feet (1,221 metres), has erupted several times since the 18th century, and the region continues to be seismically active.