airfields across the island. 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, while a naval anchorage was constructed at Tonolei Harbor near Buin on the southern coastal plain, along with anchorages on the Shortland Islands group. The airfield at Kahili was known by the Japanese as Buin Airfield, 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. 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. These forces constituted the Japanese 17th Army, commanded by General Harukichi Hyakutake. 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. 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. Allied planning Choice of Bougainville Reduction of the main Japanese base at Rabaul was the ultimate goal of the Allied offensive in the Solomons. To achieve this, Allied planners formulated Operation Cartwheel. By 1943 Rabaul was already within range of Allied heavy bombers, but a closer airfield was needed for light bombers and escort fighters. Thus, the entire island of Bougainville did not need to be occupied; only enough relatively flat land to support an airbase was required. According to Morison this "was the one and only reason why the JCS authorized Halsey to seize a section of Bougainville: to establish forward airfields for strikes on Rabaul." The area around Cape Torokina was settled on since, among other things, the Japanese were not there in force and had no airfield there. Also, Empress Augusta Bay had a