The battle of Salamaua (30 June-11 September 1943) was the first stage in the Allied campaign in north-eastern New Guinea, and saw Australian troops slowly push forwards across difficult terrain, pulling the Japanese away from their major base at Lae, further up the coast.
The Japanese had first occupied Lae and Salamaua in the spring of 1942. The small Australian garrison on the coast had retreated inland to Wau, where there was a pre-war airstrip, and was supported there by air. Early in 1943, after the failure of their attempt to reach Port Moresby along the Kokoda Trail, the Japanese launched an attack on Wau (28-30 January 1943), but this was also repulsed and they retreated to the coast. The Australians followed, and by the end of February had reached the area south of the village of Mubo.
In late March 1943 General MacArthur and Admiral Halsey's commands produced the Elkton III plan, aimed at the conquest or isolation of the major Japanese base at Rabaul on New Britain. Lae and Salamaua were to be captured in the second phase of that plan, part of Operation II of Elkton III. Lae was to be captured first, followed by Salamaua. Operation I was to be rather less ambitious, and involved landings on undefended Woodlark Island and Kiriwina Islands.
Although the overall shape of the Elkton III plan was followed in Operation Cartwheel, the details were changed. Even before the start of Operation I/ Operation Chronicle, the Australians were pressing the Japanese from their base at Wau. They were supported by an amphibious landing at Nassau Bay, south of Salamaua, on 30 June 1943 (the same day as Operation Chronicle). The Japanese were then kept under constant pressure at Salamaua in the period between Operations I and II, and the Australians were already close to the settlement when Operation Postern, the implementation of Operation II, finally began on 4 September. It soon became clear to the Japanese that they couldn't hold Lae or Salamaua, and both places were evacuated. Salamaua fell on 11 September and Lae on 16 September.
The Australian advance resumed in May 1943, after a pause imposed by a lack of transport aircraft and shipping in the South-west Pacific Theatre. Wau had been garrisoned by the Australian 3rd Division, and it was the 17th Brigade from that division that took part in the fighting in the mountains. They were repeatedly held up in the area to the south of Mubo, but eventually managed to find a way to the coast by heading along the southern side of Lobadabia or Lababia Ridge
On 30 June 1,400 troops from the US 32nd Division landed at Nassau Bay, south of Salamaua, and quickly joined up with the Australians.
General Hotazo Adachi, commander of the Japanese 18th Army, believed that Salamaua was essential to the defence of Lae, and moved 9,000 of the 11,000 men he had in the area to Salamaua.
The direction of the fighting around Salamaua was strongly influenced by the location of the few usable trails. One key trail ran east from Wau to Mubo village, then turned north, passing Mt Tambu, to reach Salamaua. A coastal trail ran from Nassau Bay to Salamaua. A third trail crossed the mountains a little further north, and joined the Mubo route just north of Mt Tambu. North of Mt Tambu were features that became known as Scout Ridge and Roosevelt Ridge. Roosevelt Ridge was almost on the coast, next to Tambu Bay.
The allied lines now ran west from Nassau Bay, then curved north and ran parallel to the coast, about three miles inland. The Japanese now possessed a narrow strip of land that ended at Mubo. The Australians began a major assault on Mubo on 7 July, and after a few days of fighting the Japanese abandoned the village and fell back to Mt Tambu.
The next major Australian target was Tambu Bay, to the north-east of the mountain. Possession of the bay would allow the 3rd Division to be supplied by sea, instead of by air to Wau and porter across the mountains. The Allies carried out a two-pronged attack on Mt Tambu. Attacking from the west Australian troops established a foothold on the northern slopes on 16 July, where they resisted Japanese counterattacks, but for some time were unable to make any more progress. On the coast Papua troops fighting with the Americans advanced north, and an amphibious force captured the bay late in July. Allied artillery was in action from Tambu Bay from 27 July.
The deadlock at Mt Tambu was broken in mid August. Australian patrols discovered that the Japanese weren't defending the ridge that ran north from the mountain and on 12 August they occupied it from the west. On 13 August American troops captured Roosevelt Ridge, north-east of the mountain, and on 16 August the two attacks met up, surrounding the Japanese garrison on the mountain. The Japanese decided to fight their way out, and on 19 August managed to withdraw to the Francisco River, the last defensive position south of Salamaua. During the rest of August the Allies focused on clearing the Japanese from the area south of that river, and preparing to cross to the north bank.
The fate of Salamaua was now decided by events further north. The main offensive against Lae, originally planned as Operation II, was implemented as the start of Operation Postern. D-Day for Postern was set at 4 September 1943, and on that day Australian troops landed on the coast east of Lae. On the following day US paratroops captured Nadzab, inland to the west of Lae. The Japanese now realised that Salamaua and Lae could no longer be held, and decided to retreat towards Finsschhafen at the tip of the Huon Peninsula. On 11 September American troops made an unopposed entry into Salamaua, and four days later Lae followed. The first stage of Operation Postern - the Salamaua-Lae Campaign - was over.