Map - Kwajalein Atoll (Kwajalein Atoll)

Kwajalein Atoll (Marshallese: Kuwajleen ) 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 6 mi2. It lies in the Ralik Chain, 2,100 nmi southwest of Honolulu, Hawaii.

The US Navy has hosted a naval base on Kwajalein Island since World War II. It was the final resting place of the German cruiser Prinz Eugen after it survived the Operation Crossroads nuclear test in 1946. In the late 1950s, the US Army took over the base as part of their Nike Zeus anti-ballistic missile efforts, and since then the atoll has been widely used for missile tests of all sorts. Today it is part of the Ronald Reagan Ballistic Missile Defense Test Site, with various radars, tracking cameras, missile launchers, and many support systems spread across many islands. One of the five ground stations used in controlling the operation of the Global Positioning System (GPS) navigation system is located on Kwajalein.

Kwajalein is the 14th largest coral atoll as measured by area of enclosed water. Comprising 97 islands and islets, it has a land area of 16.4 km2 (6.33 mi²) and surrounds one of the largest lagoons in the world, with an area of 2,174 km2 (839 mi²). The average height above sea level for all the islands is about 1.8 m.

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 degrees. Underwater visibility is typically 100 ft on the ocean side of the atoll.

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. Roi-Namur is about 70 km east of Ebadon and 80 km NWN of Kwajalein. The atoll is 2100 mi from Honolulu, 2000 mi from Australia, and 2100 mi from Japan. Kwajalein Island is about 500 mi north of the equator.

Islands 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.