although in reality it was actually more than 40,000. Against this, the Australians deployed Lieutenant General Stanley Savige's II Corps, consisting of the 3rd Division and the 11th Brigade in November 1944. The troops were Militiamen, part of Australia's reserve military, consisting of volunteers and conscripts. Although their ranks included some Second Australian Imperial Force soldiers and officers who were veterans of earlier campaigns in the Middle East and New Guinea, they were largely inexperienced having served primarily in a garrison role in Australia and New Guinea prior to their commitment to Bougainville. In December, after a period of reconnaissance and information gathering, it was decided that the Australians would pursue an aggressive campaign to clear the Japanese from Bougainville. The campaign subsequently developed into three separate drives by the Australians, who fanned out from the main Allied base at Torokina: in the north, centre and southern parts of the island. The first actions were fought around the seizure of Pearl Ridge in late December 1944 to secure control of the east–west avenues of approach across the island, and to prevent any possible Japanese counter-attacks against Torokina. This was followed by actions in the north, where it was planned that Japanese forces would be forced into the narrow Bonis Peninsula and contained, while the main drive took place in the south, where the main Japanese forces were concentrated, with an initial drive towards Mosigetta, followed by an advance towards Buin on the coast. The drive south subsequently resulted in several actions around Slater's Knoll and around the Hongorai River. Preliminary moves In the northern sector of the island, in February 1945, Major General Kesao Kijima—commander of the Japanese 38th Independent Mixed Brigade— had ordered a withdrawal to Numa Numa, following the fighting around Tsimba Ridge. He subsequently left a force of 1,400 sailors drawn from the 87th Naval Garrison Force and 2,000 civilians to hold the Bonis Peninsula. Of these civilians, about 600 were armed, although only half were trained to undertake a combat role. As their supplies dwindled, in May–June the Japanese sailors—under the command of Captain Eikichi Kato, the senior naval officer in Buka—began to raid the Australian supply lines between Ruri Bay and Ratsua as they attempted to hold a position between Porton Plantation and Tarbut. Meanwhile, Australian troops from the 11th Brigade had continued their advance north from Tsimba Ridge in April–May, clearing up to the