 The United States launched an assault on the main islands of Kwajalein in the south and Roi-Namur in the north from January 31, 1944, to February 3, 1944.The Japanese defenders put up a stiff resistance though outnumbered and under-prepared.Although the United States won the battle the determined defenses of Roi-Namur left only 51 Japanese survivors of an original garrison of 3,500.