ブーゲンビル島沖海戦
In 1942, Bougainville was occupied by Japanese forces, who used it as a base to attack Guadalcanal and other Allied territory. In November 1943, the 3rd Marine Division landed on the west coast of Bougainville. Shortly afterwards the Battle of Empress Augusta Bay was fought between cruisers and destroyers of the U.S. Navy and the Imperial Japanese Navy. The Americans routed the Japanese and took control of the seas in this area. A concerted Allied land offensive between November 1943 and April 1944 was needed to occupy and hold the part of the island along the western shore in an area called "Torokina". The Americans set about establishing a wide defensive perimeter, draining swamps, and building multiple airfields for defence. Their next goal was to attack the Japanese on New Britain Island. The Marines were replaced by US Army troops.