The South West Pacific Area, which included Australia, Indonesia, and the Philippines came under General Douglas MacArthur as supreme commander.

[3] The Japanese reaction to Task One, the seizure of the southern part of the Solomon Islands, was more violent than anticipated and some months passed before the Guadalcanal Campaign was brought to a successful conclusion.

[4] Following these victories, the initiative in the South West Pacific passed to the Allies and General Douglas MacArthur pressed ahead with his plans for Task Two.

[10] The Markham River originates in the Finisterre Range and flows for 110 miles (180 km), emptying into the Huon Gulf near Lae.

The Markham Valley was traversable by motor vehicles in the dry season, which ran from December to April, and therefore formed part of a natural highway between the Japanese bases at Lae and Madang.

A model of the Lae-Salamaua area was constructed in a secure room at St Lucia, the windows were boarded up and two guards were posted on the door round the clock.

On 16 May, Blamey held a conference with Berryman and Lieutenant General Sir Edmund Herring, the commander of I Corps, around the model at which the details of the operation were discussed.

Meanwhile, Major General George Alan Vasey's 7th Division, in a reprise of the Battle of Buna–Gona in 1942, would advance on Lae from the west by an overland route.

[15] Its primary role was to prevent reinforcement of the Japanese garrison at Lae by establishing itself in a blocking position across the Markham Valley.

[17] The POSTERN plan called for the 7th Division to move in transports to Port Moresby and in coastal shipping to the mouth of the Lakekamu River.

[19] MacArthur agreed to make the 2nd Battalion, 503rd Parachute Infantry Regiment based at nearby Gordonvale, Queensland, available to New Guinea Force to capture Nadzab.

Colonel Kenneth H. Kinsler, the commander of the 503rd, eager to discuss the Battle of Crete with the 21st Infantry Brigade's Brigadier Ivan Dougherty, took the unusual step of parachuting into Ravenshoe.

Blamey made the Australian Army transport MV Duntroon available to ship the regiment from Cairns to Port Moresby,[21] except for the 2nd Battalion and advance party, which moved by air as originally planned.

[23] To give the paratroops some artillery support, Lieutenant Colonel Alan Blyth of the 2/4th Field Regiment proposed dropping some of its eight short 25-pounders by parachute.

[29] Transport aircraft were controlled by the 54th Troop Carrier Wing, which was commanded by Colonel Paul H. Prentiss, with his headquarters at Port Moresby.

Ideally, Z-Day would be clear from Port Moresby to Nadzab but foggy over New Britain, thereby preventing the Japanese air forces at Rabaul from intervening.

"Not a single squadron," wrote General Kenney, "did any circling or stalling around but all slid into place like clockwork and proceeded on the final flight down the Watut Valley, turned to the right down the Markham, and went directly to the target.

[36] Following the transports came five B-17s with their racks loaded with 300 lb (140 kg) packages with parachutes, to be dropped to the paratroopers on call by panel signals as they needed them.

A group of 24 B-24s and four B-17s, which left the column just before the junction of the Watut and the Markham attacked the Japanese defensive position at Heath's Plantation, about halfway between Nadzab and Lae.

[45] The small river-borne task force included ten British 5-ton folding assault boats and Hoehn military folboats.

Using the folding boats and local timber, they constructed a pontoon bridge, allowing the whole force to cross the river safely with all their equipment.

[50] The first plane to land was an L-4 Piper Cub at 0940 6 September, bringing with it Colonel Murray C. Woodbury, the commander of the U.S. Army's 871st Airborne Engineer Aviation Battalion.

On 7 September, reveille was sounded for the 2/33rd Infantry Battalion at 03:30 and the unit boarded trucks of the 158th General Transport Company that took it to marshalling areas near the airfields in preparation for the movement to Nadzab.

[52] At 04:20, B-24 Liberator 42-40682 "Pride of the Cornhuskers" of the 43rd Bombardment Group piloted by 2nd Lieutenant Howard Wood set out from Jackson's Airfield on a reconnaissance sortie to Rabaul, with a full load of 2,800 imperial gallons (13,000 L) of fuel and four 500 lb (230 kg) bombs.

[57] North of the main advance, a patrol from Lieutenant Colonel John J. Tolson's 3rd Battalion, 503rd Parachute Infantry Regiment, encountered a force of 200 Japanese crossing the Bumbu River on 15 September.

As they moved down the Markham Valley Road, they occasionally encountered sick Japanese soldiers who held the column momentarily.

The column entered Lae unopposed by the Japanese but aircraft of the Fifth Air Force strafed the 2/33rd Infantry Battalion and dropped parachute fragmentation bombs, wounding two men.

After discussing the matter with Imperial General Headquarters in Tokyo, Imamura and Adachi called off their plans to capture Bena Bena and Mount Hagen and instructed Nakano and Shoge to move overland to the north coast of the Huon Peninsula while the 20th Division moved from Madang to Finschhafen, sending one regiment down the Ramu valley to assist the 51st Division.

[14] The development of Nadzab depended on heavy construction equipment which had to be landed at Lae and moved over the Markham Valley Road.

Imperial General Headquarters had regarded the defeats in the Guadalcanal Campaign and Battle of Buna–Gona as setbacks only, and had continued to plan offensives in the South West Pacific.