In March the group provided the RAAF's contribution to the Battle of the Bismarck Sea, "the decisive aerial engagement" in the SWPA according to General Douglas MacArthur, resulting in twelve Japanese ships being sunk. Between July and October 1943, No. 9 OG was expanded to include a works wing and a radio location wing, its complement of operational squadrons totalling nine, plus a torpedo bomber detachment. Its aircraft carried out operations against enemy bases, shipping and lines of communication along the coast of New Britain. In October–November the group launched a number of major assaults on Rabaul, bombing and strafing ground and naval targets.