The Japanese had captured Bougainville in early 1942, and had subsequently built it into a significant base with large numbers of aircraft and troops, in order to protect the fortress at Rabaul. Following this, Allied planners determined that their key strategy in the region would be reduction of the base at Rabaul. To do this, they needed airfields within range, and as such, it was decided to secure the western part of Bougainville, landing around Torokina in November 1943. Heavy fighting followed the landing, but after a large-scale Japanese counter-attack was defeated in March 1944, the Japanese withdrew from the US lodgement and subsequently a period of relative quiet followed as the US forces limited themselves to patrolling and establishing outposts, rather than large-scale operations.