The Hawaiian Islans, once known as the Sandwich Islands, form an archipelago of 19 islands and atolls, numerous smaller islets, and undersea seamounts trending northwest by southeast in the North Pacific Ocean between latitudes 19° N and 29° N. The archipelago takes its name from the largest island in the group and extends some 1,500 miles (2,400 km) from the Island of Hawaiʻi in the south to northernmost Kure Atoll. Excluding Midway, which is an unincorporated territory of the United States, the Hawaiian Islands form the U.S. State of Hawaii.