General Blarney's planning for an attack on Lae involved landing a force by sea. This in turn demanded the prior seizure of a shore base within a hundred kilometres of Lae, which was considered the maximum range for the type of landing craft that would carry the assault troops. Nassau Bay, midway between Morobe and Lae, was selected as the most suitable area. Its capture would also enable a junction to be made with the Australian forces operating at Mubo. General MacArthur also saw the Nassau Bay landing as a means to ease the logistic situation that was tying up the troop carrier squadrons and native labour resources. Herring wrote, ‘It seemed essential that we should get hold of it as soon as possible.’ On 27 May 3rd Division headquarters was given orders to secure Nassau Bay using infantry from the United States 41st Infantry Division.

The 41st Infantry Division comprised the National Guard units of the north-western states of the United States. Originally drawn from the states of Oregon, Washington, Idaho and Montana, the division was known as the ‘Sunsetters’ and had a half-circle sunset motif. The division was deployed to the Pacific theatre in March 1942, and had arrived in Melbourne in three convoys by mid-May. The division had three infantry regiments, the 162nd, 163rd and 186th, three artillery battalions, the 146th, 205th and 218th, as well as ancillary units.