A mixture of combat and service troops operated in western New Britain. The 1st and 8th Shipping Regiments used motorized barges to shuttle troops and cargo along the coast from Rabaul to Cape Merkus, Cape Gloucester, and across Dampier Strait to Rooke Island. For longer movements, for example to New Guinea, the 5th Sea Transport Battalion manned a fleet of trawlers and schooners, supplemented by destroyers of the Imperial Japanese Navy when speed seemed essential. The troops actually defending western New Britain included the Matsuda Force, established in September 1943 under the command of Major General Iwao Matsuda, a specialist in military transportation, who nevertheless had commanded an infantry regiment in Manchuria. When he arrived on New Britain in February of that year, Matsuda took over the 4th Shipping Command, an administrative headquarters that provided staff officers for the Matsuda Force. His principal combat units were the understrength 65th Infantry Brigade—consisting of the 141st Infantry, battle-tested in the conquest of the Philippines, plus artillery and antiaircraft units—and those components of the 51st Division not committed to the unsuccessful defense of New Guinea. Matsuda established the headquarters for his jury-rigged force near Kalingi, along the coastal trail northwest of Mount Talawe, within five miles of the Cape Gloucester airfields, but the location would change to reflect the tactical situation.

As the year 1943 wore on, the Allied threat to New Britain increased. Consequently, General Hitoshi Imamura, who commanded the Eighth Area Army from a headquarters at Rabaul, assigned the Matsuda Force to the 17th Division, under Lieutenant General Yasushi Sakai, recently arrived from Shanghai. Four convoys were to have carried Sakai's division, but the second and third lost one ship to submarine torpedoes and another to a mine, while air attack damaged a third. Because of these losses, which claimed some 1,200 lives, the last convoy did not sail, depriving the division of more than 3,000 replacements and service troops. Sakai deployed the best of his forces to western New Britain, entrusting them to Matsuda's tactical command.