The Bougainville campaign was a series of land and naval battles of the Pacific campaign of World War II between Allied forces and the Empire of Japan, named after the island of Bougainville. It was part of Operation Cartwheel, the Allied grand strategy in the South Pacific. The campaign took place in the Northern Solomons in two phases. The first phase, in which American troops landed and held the perimeter around the beachhead at Torokina, lasted from November 1943 through November 1944. The second phase, in which primarily Australian troops went on the offensive, mopping up pockets of starving, isolated but still-determined Japanese, lasted from November 1944 until August 1945, when the last Japanese soldiers on the island surrendered. Operations during the final phase of the campaign saw the Australian forces advance north towards the Bonis Peninsula and south towards the main Japanese stronghold around Buin, although the war ended before these two enclaves were completely destroyed. Japanese occupation Before the war, Bougainville had been administered as part of the Australian Territory of New Guinea, even though, geographically, Bougainville is part of the Solomon Islands chain. As a result, within the various accounts of the campaign it is referred to as part of both the New Guinea and the Solomon Islands campaigns. During their occupation the Japanese constructed naval aircraft bases in the north, east, and south of the island; but none in the west. They developed a naval anchorage at Tonolei Harbor near Buin, their largest base, on the southern coastal plain of Bougainville. On the nearby Treasury and Shortland Islands they built airfields, naval bases and anchorages. These bases helped protect Rabaul, the major Japanese garrison and naval base in Papua New Guinea, while allowing continued expansion to the south-east, down the Solomon Islands chain, to Guadalcanal and New Guinea and beyond. To the Allies, Bougainville would later also be considered vital for neutralizing the Japanese base around Rabaul. In March–April 1942, the Japanese landed on Bougainville as part of their advance into the South Pacific. At the time, there was only a small Australian garrison on the island which consisted of about 20 soldiers from the 1st Independent Company and some coastwatchers. Shortly after the Japanese arrived, the bulk of the Australian force was evacuated by the Allies, although some of the coastwatchers remained behind to provide intelligence. Once secured, the Japanese began constructing a number of