Kwajalein Atoll is part of the Republic of the Marshall Islands (RMI). The southernmost and largest island in the atoll is named Kwajalein Island, which its majority English-speaking residents (about 1,000 mostly U.S. civilian personnel) often use the shortened name, Kwaj. The total land area of the atoll amounts to just over 16 km2. It lies in the Ralik Chain, 2,100 nautical miles (3,900 km) southwest of Honolulu, Hawaii.

The average height above sea level for all the islands is about 1.8 meters.

The atoll was made when volcanoes on the seabed from 165–76 mya built up enough lava that the land rose from beneath the sea. It cannot be determined how far above sea level the original land rose. Then coral started growing around the land/volcano, about 56 mya. Then the land subsided leaving the coral ring of the atoll. The water temperature averages 81 °F (27 °C) degrees.

The atoll has an extended oval shape running roughly WNW - ESE on the western side and then bending to run almost due south on the eastern side. It is framed by its three largest islands, Ebadon, Roi-Namur and Kwajalein, which are located at the extreme western, northern, and southern points, respectively. 

slands often have alternate names: The first is the Marshallese name, the second was assigned somewhat arbitrarily by the U.S. Navy prior to their attack on the atoll during World War II. The original name was considered too difficult for English speakers to properly differentiate among the islands. The latter has often been retained by English speakers. The exception to this is Kwajalein itself, which is close to the native name; the received spelling is from German, however.

According to Wikipedia