coral formation in the Ralik (western) chain of the Republic of the Marshall Islands, in the western Pacific Ocean. The string of some 90 islets has a total land area of 6 square miles (16 square km) and surrounds the world's largest lagoon (655 square miles 【1,722 square km】). The islets of Kwajalein, Roi, and Namur were the first of the Marshall Islands captured by U.S. troops in World War II. The atoll serves as a seaport, an air stop, and a U.S. military missile testing site. Pop. (1988) 9,311.