During the campaign in the northern Solomons, Southwest Pacific forces had been pushing forward on the other prong of the offensive in New Guinea and western New Britain. The 5th Australian Division, with the help of a U.S. Army regiment, took Salamaua on 11 September 1943. Meanwhile, the 9th Australian Division and a U.S. Army Engineer Special Brigade had landed east of Lae on 4 September. The next day a regiment of U.S. Army paratroopers, conducting the first American airborne operation in the Pacific, flew from Port Moresby, jumped and captured Nadzab, northwest of Lae, after which the 7th Australian Division was flown into Nadzab. A coordinated attack by the 7th and 9th Australian Divisions resulted in the fall of Lae on 16 September. Lae was developed into a forward naval base while Nadzab became a major air base.

     Allied forces next moved to take Finschhafen (2 October 1943) on the eastern end of the Huon Peninsula. GEN MacArthur had hoped to trap the Japanese on this peninsula, but the survivors of Lae and Salamaua escaped overland to the north shore of the Huon Peninsula while those from Finschhafen withdrew along the coast. American and Australian troops fought more than three months, until mid-February 1944, in the New Guinea jungles before the Huon Peninsula was considered secure. Forces of both the South and Southwest Pacific were now in position for a final assault on Rabaul.