The Battle of Kwajalein was fought as part of the Pacific campaign of World War II. It took place from 31 January – 3 February 1944, on Kwajalein Atoll in the Marshall Islands. Employing the hard-learned lessons of the Battle of Tarawa, the United States launched a successful twin assault on the main islands of Kwajalein in the south and Roi-Namur in the north. The Japanese defenders put up stiff resistance, although outnumbered and under-prepared. The determined defense of Roi-Namur left only 51 survivors of an original garrison of 3,500. For the US, the battle represented both the next step in its island-hopping march to Japan and a significant morale victory because it was the first time the Americans had penetrated the "outer ring" of the Japanese Pacific sphere. For the Japanese, the battle represented the failure of the beach-line defense. Japanese defenses became prepared in depth, and the Battles of Peleliu, Guam, and the Marianas proved far more costly to the US. Background Geography Kwajalein Atoll is in the heart of the Marshall Islands. It lies in the Ralik Chain, southwest of Honolulu, Hawaii at . Kwajalein is the world's largest coral atoll and comprises 93 islands and islets, it has a land area of 1,560 acres (6.33 km2), and surrounds one of the largest lagoons in the world, measuring 324 mi2 (839 km2) in size. The two most significant land masses are Kwajalein Island in the south, and the linked islands of Roi-Namur in the north. By the start of World War II, the Marshalls (South Seas Mandate) were already an integral part of the Japanese perimeter of defense. Its facilities were being utilized as outlying bases for submarines and surface warships, as well as for air staging for future advances being planned against Ellice, the Fiji Islands, and Samoa. Gilbert and Marshall Islands campaign After the capture of Makin and Tarawa in the Gilbert Islands, the next step in the United States Navy's campaign in the central Pacific was the Marshall Island chain. These islands had been Imperial German colonies, after their purchase from Spain in 1899. At the end of World War I they were assigned to Japan in the post-war settlement as the "Eastern Mandates". The islands then became a mystery because the Japanese closed them to the outside world. It was presumed the Japanese had built illegal fortifications throughout the islands, but the precise