The Huon Peninsula Campaign (22 September 1943-24 April 1944) was part of the second stage of Operation Postern, and was conducted to clear the Japanese from the shores of the Vitiaz Strait, in order to allow the Allies to use their naval forces off the northern coast of New Guinea. This was all part of Operation Cartwheel, the wider campaign to isolate the major Japanese base at Rabaul on nearby New Britain. It came soon after the end of the Salamaua-Lae campaign, which saw the Allies expel the Japanese from their bases on the coast of the Huon Peninsula.
The Huon Peninsula campaign was fought for possession of the eastern and northern coast of the Huon Peninsula, which gave the Japanese control of the Vitiaz Strait, between New Guinea and New Britain. The first Allied target was the old German port of Finschhafen, at the eastern end of the peninsula, but most of the fighting would take place just to the north, where for once there were important settlements away from the coast. The coast track ran north to Katika and then Gusuka. One track ran inland from the Katika area to Jivevaneng and then Sattelberg, while a second ran from the Gusika area inland to Wareo. The Japanese would make a stand in the Wareo and Sattelberg areas, and even launch counterattacks against the narrow Australian coastal positions.
The bulk of the fighting was carried out by the Australian 9th Division (Major-General G.F. Wooten), with American support (in particular naval support). The first stage was the capture of Finschhafen, a former German possession at the eastern end of the peninsula. The Australians decided to carry out a two pronged assault, with one brigade landing north of the port, while a second advanced along the coast from the direction of Lae to act as a diversion.
The amphibious landing was carried out by the 20th Brigade. The brigade landed at Scarlet Beach (the name was chosen to avoid confusion with an active Red Beach in the Huon Gulf), on the morning of 22 September. Japanese resistance was limited, and the beachhead was soon secured (despite a fairly chaotic landing). On the same day the 22nd Battalion began to march east along the coast from Lae to distract the Japanese. Over the next few days the 20th pushed south, sometimes outflanking strong Japanese positions. The final attack on Finschhafen was launched from the west. The Japanese put up fierce resistance outside the town, but when it was clear that it was about to fall the last defenders pulled out to the north-west. The Australians captured Finschhafen on 2 October, where they captured documents suggesting that the Japanese were planning a major counterattack.
On 16 October the Japanese launched a three pronged counterattack, with the 79th and 80th Regiments attacking east towards Scarlet Beach and an amphibious force attacking on the following day. The 80th Regiment was held up at Jivevaneng, on the track between Sattelberg and the beach, and the amphibious force was destroyed, but the 79th Regiment actually reached the beach, and for a few days the Australian beachhead was split in two. The Japanese eventually ran out of steam, and on 19 October an Australian counterattack forced them away from the beach. The Japanese lost 1,500 men during the fighting for Finschhafen, but they had failed in their main attempt to retake the port.
The Australians were now free to go onto the offensive. Their first target was Sattelberg, west of their main landing beach. First they had to clear the Japanese from a roadblock on the road between the coast and an isolated Australian position at Jivevaneng. This block was finally cleared on 2 November, leaving the road open for the main attack on the difficult Sattelberg position. This developed into a two pronged assault, with one force following the Sattelberg Road as it ran along a ridge to the south-east of the town, then turned north to climb the steep Sattelberg Hill. A second force attempted to advance to the right, moving north to a parallel ridge, then west to Sattelberg Hill. The early stages of the attack were supported by nine Matilda tanks, although they couldn't take part in the final climb up Sattelberg Hill. The attack began on 16 November, and despite fierce resistance the Australians began to advance up Sattelberg Hill on 22 November. It took another two days for the Americans to reach the top of the hill, at which point the Japanese retreated north to Wareo. The Australians occupied Sattelberg on 25 November.
Next came the attack on Wareo. This was a difficult manoeuvre, which involved dropping down from Sattelberg Hill into the Song valley, then up a steep hill to attack Wareo. At the same time a second force attacked near the coast to cut the remaining Japanese supply line. The 26th Brigade began the attack across the Song on 28 November. By the end of the day they were across the Song, and on 1 December they captured a key Japanese position at Kuanko. The success of the two Australian attacks convinced the Japanese to pull back towards their main base at Sio, a Japanese held port that was nearer the 18th Army's HQ at Madang. In order to give their forces a change to escape they launched counterattacks on the Australian position at Kuanko, which held them up until 7 December. Wareo finally fell on 8 December, and on 10 December the two Australian brigades met up on the trail from Wareo to Gusika on the coast.
After the end of the fighting for Wareo the Australians were free to advance along the coast. The advance began on 5 December when the 29th/46th Battalion began to advance from Gusika. The Japanese conducted a fighting retreat, causing frustrating casualties but rarely holding up the Australian advance for any prolonged period. Their aim was to win time for the 20th Division to complete its retreat from the lost areas further south.
By 10 December the Australians were at Kilgia. Cape Sidiba was reached by 16 December and their main target at Fortification Point by 20 December. This was the point where the coast turned to the north-west and ran around the Huon Peninsula towards the Japanese base at Sio. The advance continued at a steady pace. Wandokai was captured on 24 December, Nanda on 31 December and by 2 January 1944 the Australians had reached Sialum Island, with a useful anchorage.
On 2 January the nature of the campaign changed when the US 32nd Division landed at Saidor, west of the Japanese base of Sio. They quickly established themselves, and threatened to cut the Japanese lines of retreat. After the American landing at Saidor, Adachi travelled by submarine from his HQ at Madang to Sio, to assess the situation for himself. In consultation with his superiors at Rabaul he decided to order a full scale evacuation of the remaining Japanese troops on the Huon Peninsula. Some of the troops at Sio were evacuated on the few available barges, but about 14,000 men from the 20th and 51st Divisions, had to travel on land. Their route took them along the coast until they were closer to Saidor, and then inland across some of New Guinea's very difficult terrain.
After a difficult return trip Adachi reached Madang on 11 January. It took his men another six weeks to join him. Around 10,000 survivors from the two divisions reached Madang on 1 March, having evaded the Allied trap. There was some criticism of the army leadership at Saidor, where the troops remained on the defensive for rather too long. This left a gap between them and the Australians fighting in the Finisterre Range, and the Japanese escaped through this gap. The Japanese posted 2,000 men on the inland route past Saidor,
The Japanese were only just ahead of the Allies. The Australians pushed along the coast, reaching Sio on 15 January 1944. The Australian 9th Division was then relieved by the Australian 5th Division,
The Australians coming along the coast from the east joined up with the US troops at Saidor on 10 February. On 5 March US troops landed further west, at Yalau Point. This involved 54 craft and 1,348 troops, but little opposition. Soon after this landing the Americans met up with Australian troops advancing north across the Finisterre Range from the Ramu Valley.
At this point the Allies were still expecting to have to fight a difficult battle at Madang, where Adachi had a sizable garrison. Before launching this attack MacArthur decided to capture the Admiralty Islands, on the opposite side of the Bismarck Sea north of Madang. US troops landed on Los Negros on 29 February and on Manus on 12 March. By the end of March the islands had been secured. Adachi now decided that Madang was no longer tenable, and ordered a retreat towards Wewak and Hansa Bay, the next major Japanese bases along the coast.
In the first part of April the Australians fought a number of minor battles with the Japanese on the Bogadjim Road, and on 13 April the first Australian patrol reached an undefended Bogadjim. On 15 April an American patrol coming from the east joined them. The capture of Bogadjim was officially announced by the BBC and ABC on 17 April.
The allies then advanced north, but when they reached Madang on 24 April (after a some what undignified scramble to be first into the town) they discovered that the Japanese had gone. On 25 April they occupied Alexishafen, a few miles to the north, also without opposition. Although fighting continued in the area for some time after this, the fall of Madang marked the effective end of Operation Postern, and meant that the Allies now had command of the New Guinea side of the Vitiaz Strait.
By then the Cape Gloucester area on New Britain had also been secured, so the Allies had command of both sides of the straits between New Britain and New Guinea. By this point the Americans had launched yet another surprise attack, this time landing at Aitape and Hollandia, well to the west of Adachi's new positions. Adachi was now totally isolated. Although he did launch a major attack on the Americans on the Driniumor River in late June, his army had effectively been cut off from the rest of the Japanese Empire.