Bougainville Campaign - Wikipedia

On November 1, 1943, US troops landed on Bougainville Island in the Solomon Islands. From the article:

"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. 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 invaded 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 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.

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.[6]

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.[7] 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.[8]

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.[9] Once secured, the Japanese began constructing a number of airfields across the island.[10] The main airfields were on Buka Island, the Bonis Peninsula in the north, at Kahili and Kara, in the south, and Kieta on the east coast,[10] while a naval anchorage was constructed at Tonolei Harbor near Buin on the southern coastal plain, along with anchorages on the Shortland Islands group.[11]

The airfield at Kahili was known by the Japanese as Buin Airfield,[12] and to its south was an airfield on Ballale Island in the Shortland Islands. These bases allowed the Japanese to conduct operations in the southern Solomon Islands and to attack the Allied lines of communication between the United States, Australia and the Southwest Pacific Area.[10]

At the opening of the Allied offensives, their estimates of Japanese strength on Bougainville varied widely, ranging between 45,000 and 65,000 Army, Navy, and labour personnel.[3][Note 2] These forces constituted the Japanese 17th Army, commanded by General Harukichi Hyakutake.[13] Hyukatake reported to General Hitoshi Imamura, commander of the Japanese Eighth Area Army, headquartered at Rabaul on New Britain Island. Naval command at Rabaul was the responsibility of Vice Admiral Jinichi Kusaka, commander Southeast Area Fleet. The level of cooperation between these two officers was greater than that usually found between the branches of the Japanese armed forces.[14] On Bougainville, the Japanese forces consisted of the following formations: the 17th Infantry Group – consisting of the 81st Infantry Regiment and the III Battalion, 53rd Infantry Regiment under Major General Kesao Kijima, and elements of the 6th Division. The 17th Infantry occupied northern Bougainville, while the 6th had responsibility for the island south of Tarina.[15]"