The 1942-43 defeats of the Japanese at, Kokoda, Milne Bay, around Buna and at Wau opened the way for the Allies to plan and mount the advance on the major objective of Lae, New Guinea. This large Japanese base sat on the coast near the mouth of the Markham River at the southern end of the Huon Peninsula. By capturing this area, the Allies would be able to develop airfields in the Markham Valley to support subsequent advances along the north coast.
In May 1943, General Douglas MacArthur, Commander-in-Chief of the Allied forces in the South-West Pacific Area, issued a directive for the attack on Lae. Australian forces were to capture Lae, and then continue with two advances at the same time, one around the coast of the Huon Peninsula and the other inland following the Markham and Ramu Valleys. The latter would culminate with the capture of one of the key features, Shaggy Ridge.
Ahead of the land attack Allied bombers mounted a strong campaign against the Japanese base and lines of communication, weakening the defences. The first action by Allied troops was a paratroop drop, the first in New Guinea, on 5 September 1943. The American 503rd Parachute Infantry Regiment, and some gunners of the Australian 2/4th Field Regiment, were dropped over the Markham Valley, and seized an abandoned airfield at Nadzab. Work quickly commenced to prepare the airstrip for transport aircraft to land more troops.