During late 1943 and early 1944 Allied forces in the South West Pacific Area undertook Operation Cartwheel. This was a major offensive which aimed to isolate the main Japanese base in the area at Rabaul on the north-eastern tip of New Britain, and capture airstrips and anchorages which were needed to support a subsequent advance towards the Philippines. During December 1943 and January 1944 United States Army and United States Marine Corps units successfully landed in western New Britain at Arawe and Cape Gloucester. Japanese forces in western New Britain suffered a further defeat at Talasea in March 1944. Securing the western island prevented the Japanese launching attacks against the flank of the main Allied offensive along the north coast of New Guinea. Allied operations to secure the Huon Peninsula and the Markham–Ramu Valley, on the New Guinea mainland concluded in April 1944 with the capture of Madang. The focus of Allied operations on the mainland then turned towards securing Western New Guinea. The Admiralty Islands were captured during a campaign which lasted between 29 February and 18 May 1944. On Bougainville, a strong Japanese counter-attack had been repulsed in March 1944. A period of relative quiet followed until late 1944, after Australian forces relieved the US garrison (arriving from October).