resulting Battle of Tsimba Ridge, the Australians encountered determined resistance in heavily fortified positions, and it was not until 9 February that the last Japanese dug in on the western edge of the ridge were rooted out. During the remainder of February and March the Australians drove the Japanese north past Soraken Plantation. Eventually, the approximately 1,800 Japanese fell back to a strong defensive line across the neck of the Bonis Peninsula. Because the 11th Brigade was exhausted from three weeks of jungle combat, frontal assaults were ruled out and an attempt was made to outflank the Japanese positions with an amphibious landing on 8 June. However, the landing force found itself pinned down and on the verge of being exterminated. Although Japanese losses were probably higher in the resulting Battle of Porton Plantation, the defenders received a boost in morale and the Australian command called off offensive operations in this sector for the time being. It was instead decided to contain the Japanese along the Ratsua front while resources were diverted to the southern sector for the drive towards Buin. Southern front On 28 December, General Savige issued orders to the 29th Brigade to begin the drive toward the principal Japanese concentration around Buin. After a month's fighting, the Australians were in control of an area extending twelve miles south of the Perimeter and six miles inland. Employing barges to outflank the Japanese, they entered the village of Mosigetta by 11 February 1945 and Barara by 20 February. The Australians then cleared an area near Mawaraka for an airstrip. By 5 March, the Japanese had been driven off a small knoll overlooking the Buin Road; the Australians named this promontory after Private C.R. Slater who had been wounded during the fighting. During the 28 March – 6 April Battle of Slater's Knoll, the Japanese launched a strong counterattack during which several determined Japanese attacks against this position were repulsed with heavy losses. In Gailey's words, "General Kanda's offensive was a disaster ... Indeed, the entire series of attacks by the Japanese is as inexplicable as the Australians' desire to conquer all the island." Having learned a costly lesson about the ineffectiveness of banzai charges, Kanda pulled his men back to a defensive perimeter around Buin and reinforced them with the garrisons from the Shortlands and the Fauros. The concentration was not complete until July. Savige took two weeks to