The Salamaua-Lae Campaign (30 June-16 September 1943) was the first part of Operation Postern, a wider offensive aimed at eliminating the Japanese presence on the New Guinea side of the Vitiaz Strait.
The Japanese had occupied Salamaua and Lae, on the Huon Gulf, in March 1942. At first these bases were seen as the front line of the Japanese defensive cordon in the area, but the Japanese then decided to expand into Papua, the south-eastern corner of New Guinea. Salamaua and Lae thus became support bases during the Battle of the Kokoda Trail (23 July-13 November 1942). After the failure of the Japanese advance on Port Moresby the focus turned to the Japanese bridgehead at Buna and Gona on the north coast of Papua, but these had been captured by 22 January 1943. About 5,400 Japanese escaped from this area and retreated along the coast to Salamaua and Lae.
In April 1943 General MacArthur and Admiral Halsey agreed the Elkton III plan. This was a three stage plan designed to isolate the powerful Japanese base at Rabaul on New Britain. While Admiral Halsey would operate in the Solomon Islands, General MacArthur's part of the plan would take place on New Guinea and New Britain. Operation I of the Elkton III plan called for the capture of Woodlark and Kiriwina Islands, off the eastern tip of Papua. This was implemented as Operation Chronicle (30 June 1943), without any Japanese resistance.
The second part of the Elkton III plan, Operation II, called for the capture of Salamaua, Lae, Finschhafen and Madang. This was implemented as Operation Postern, and would take from 30 June 1943 until 26 April 1944 to complete. The first part of this wider operation was the capture of the key Japanese bases at Salamaua and Lae.
The Japanese were well aware that their bases were under threat. In January 1943 they tried to eliminate the small Australian garrison of Wau, an inland town about 30 miles across the mountains from Salamaua, but were repulsed. In March they attempted to rush reinforcements to the area by sea, but the troop convoy was detected by Allied aircraft and destroyed. All eight transport ships and four of the eight destroyers involved were sunk and 3,000 troops drowned (Battle of the Bismarck Sea, 2-4 March 1943). Even so the Japanese still had around 11,000 men in the area, under the command of the very able General Aachi.
The first step towards the conquest of Salamaua was carried out as part of Operation I. On the night of 29-30 June 1,400 troops from the US 32nd Division landed at Nassau Bay, south of Salamaua. The next move came from Wau. The Australian 17th Brigade crossed the mountains and captured the village of Mubo on 17 July. From Mubo the Australians captured Mount Tambu and began to close the net around Salamaua. The Japanese decided that Salamaua was lost, and evacuated the town. American troops entered Salamaua on 11 September.
The attack on Lae also involved a two pronged assault. On 4 September troops from the Australian 9th Division landed on the coast east of Lae. On the following day the US 503rd Parachute Regiment captured the airfield at Nadzab, up the Markham River from Lae. They then joined with the Australian 7th Division, which had been flown into Marilinan, up a tributary of the Markham a little earlier.
These forces then converged on Lae. The Japanese put up fierce resistances, but the town fell on 16 September. The troops coming from the west reached the town first.
The Japanese suffered the heavier casualties during the campaign, despite being on the defensive. In total they suffered about 10,300 casualties, of which 2,722 were dead. The Australians bore the brunt of the fighting on the Allied side, with 500 dead and 1,300 wounded, while the Americans lost 81 dead and 396 wounded. The Japanese did manage to get around 9,000 safely out of the area.
After the capture of Salamaua the allied armies divided in two, and carried out separate thrusts, both aimed at the major Japanese base at Madang. There were two possible routes to Madang - around the coast of the Huon Peninsula or up the Markham Valley and down the Ramu Valley. The Allies decided to take both routes. The 9th Australian Division went west, and was soon heavily engaged in the Finisterre Mountains, while the 7th Division moved east onto the Huon Peninsula to attack Finschhafen, at the tip of the Peninsula.