U.S. Marines and Army forces invaded Kwajalein Atoll and nearby Roi and Namura Atolls in the Marshall Islands on January 31, 1943; breaching the outer ring of the Japanese Pacific territories. The Force included 53,000 assault troops and 1,100 land and carrier based aircraft. This was the first time Underwater Demolition Teams (UDT) were used to reconnoiter and destroy beach obstacles prior to an amphibious landing. Success in the Marshall Islands would give U.S. forces a major staging area for the dive in the Central pacific and to the Mariana islands, including Saipan and Guam.