Soraken Peninsula, which was captured by the middle of the month by the 26th Infantry Battalion. Throughout May, the 26th had also carried out an amphibious landing on Torokori Island. Meanwhile, throughout the same time the 55th/53rd Infantry Battalion had advanced north-east "through mangrove swamps...and rugged foothills" from the Soraken Plantation towards Pora Pora; this was occupied by early May and from there the Australians ranged north to Ruri Bay, establishing a line across the Bonis Peninsula over a distance of . By the end of May, the Japanese fell back behind a series of fortified positions along the base of the Bonis Peninsula. The 26th Infantry Battalion subsequently replaced the 55th/53rd, but the Australian advance came to a halt. In an effort to break this resistance and allow the northwards advance to continue, the Australians attempted to outflank the Japanese defensive line by launching an amphibious landing at Porton Plantation on 8 June. The plan called for a reinforced company from the 31st/51st Infantry Battalion to land behind the Japanese positions and attack from the west, while the main force consisting of the remainder of the 31st/51st Infantry Battalion and the 26th Infantry Battalion attempted to break through from the south. Due to poor planning, inadequate resources and strong Japanese defence, the landing failed at considerable cost to Australians, and as their efforts turned towards effecting a withdrawal from the beachhead and rescuing the stranded men, the attempt by the main force to break through from Ratsua also failed as tired troops came up against strong Japanese defensive positions. Battle Following the failed landing by the Australians at Porton Plantation, the commander of the Australian II Corps, Savige, decided to focus the main effort of the Australian campaign upon driving south towards the Japanese garrison at Buin, where the bulk of the Japanese forces were holding out. In order to concentrate enough forces for the next phase of the operation, Savige decided that the 11th Brigade, which had been carrying the advance north, should be relieved so that it could be transferred to the south following a period of rest and reorganisation. Nevertheless, there was still a need to maintain the pressure upon the Japanese in the north, and so the 23rd Brigade—which had been previously operating in the central sector after being transferred from garrison duty in the Outer Islands—was also given responsibility for the northern sector as