Bonin Islands,(Japanese: Ogasawara Gunto), a group of about 30 small volcanic islands in the Pacific Ocean. They lie about 600 miles (960 km) south of Tokyo and have an area of about 40 square miles (100 km2). The islands are administered by the Tokyo Metropolitan government. The Bonins were annexed by Japan in 1876, and during World War II they were strategic outposts in Japan's defense. United States forces occupied the islands in 1945. They were administered by the United States until 1968, when they were returned to Japan.