Following the successful conquest of New Britain in the Solomon Islands, U.S. Forces refocused its next mission on the island of Bougainville. The island was defended by more than 40,000 Japanese, but possession of an airbase there would allow U.S. forces to counter the Japanese air base at Rabaul. U.S. Marines made a surprise landing at Bougainville on November 1, 1943, encountering little resistance.