The Finisterre Range campaign (17 September 1943-24 April 1944) saw Australian troops successfully push the Japanese out of a series of strong defensive positions on incredibly difficult mountainous terrain in the Finisterre Mountains of New Guinea, preventing them from interfering with operations further east on the Huon Peninsula. The campaign was fought as part of Operation Postern, the Markham Valley/ Huon Peninsula campaign, itself part of Operation Cartwheel, the series of operations designed to isolate the Japanese base at Rabaul on New Britain.
After the fall of Lae and Salamaua on the Huon Gulf the Australians advanced in two directions. The 9th Division was sent east to attack Finschhafen, at the eastern tip of the peninsula, while General Vasey's 7th Division was sent west to secure the Markham and Ramu valleys. These two valleys formed a deep west-east trench running parallel to the north coast of New Guinea, separated from the coast by the Finisterre Mountains. The Markham ran east, reaching the Huon Gulf near Lae, while the Ramu ran west for some way, eventually reaching the coast some way to the west of the main battlefields.
The Japanese had made some efforts to build a road that would have linked Wewak and Madang to Lae. This would have allowed them to use large ships to move troops to Wewak, then trucks to get them relatively safely to Lae. Most of this road was never completed, but some progress was made on the stretch over the Finisterre Range, and work on this stretch of the road continued after the fall of Lae and Salamaua. This became known as the Bogadjim Road, after the village where it left the coast. It followed the Iowaro River inland, then cut across the mountains to the Mindjim valley, where it followed that river upstream to Yokopi. After that smaller tracks continued past Saipa and Paipa to reach Kankiryo at the top of the valley. The tracks then ran down the Faria River towards the Ramu Valley. The western side of this valley was bordered by a high mountain ridge that became known as Shaggy Ridge.
The difficult terrain and lack of roads meant that airfields would be important. One major focus of the advance west would thus be the need to seize suitable areas for airfields and then to defend them against the Japanese, who still held positions in the Finisterre Mountains to the north.
The first Australian target was Kaiapit, high up the Markham Valley, where there was a cluster of villages and an airfield. The Papuan Infantry Battalion advanced west up the Markham Valley to scout out the area. An improvised airfield was built near Kaiapit, and on 17 September the 2/6th Independent Company flew into the new airfield. On 19 September they ran into Japanese patrols outside the village, but they were able to capture Kaiapit on 20 September after some heavy fighting. They were subjected to counterattacks by troops from the Japanese 78th Regiment, which had just crossed the truck road, but these were repulsed.
The first aircraft landed on Kaiapit airfield on 21 September, and on 21-22 September the 2/16th Battalion was flown into the new base. The 2/27th Battalion followed on 23 September, to replace the 2/6th Independent Company. The 25th Brigade began to arrive on 27 September. After that reinforcements were limited for some time by the heavy fighting around Finschhafen on the Huon Peninsula.
Further west patrols from Bena Force had already reached into the Ramu Valley, where they had clashed with the Japanese west of Dumpu. The patrols were followed by the 21st Brigade on 30 September, and Dumpu was captured on 4 October, as the Japanese were withdrawing. The Japanese aided this advance by abandoning plans for a counterattack in the main valleys, and instead focusing on the routes across the Finisterre Range, and in particular Kankiryo Saddle and the surrounding ridges (most famously Shaggy Ridge to the south-west of the saddle). The defenders were commanded by Major-General Makai, whose orders were to hold the mountains. During October both side's attention was focused on the Finschhafen battle.
While the Australian 7th Division concentrated on expanding its control of the two valleys, the US Fifth Airforce built a large airfield at Gusap, half way between Kaiapit and Dumpu. This would allow them to make a major contribution to the fighting to come.
A key moment came on 5 October when a small Australian force captured a hill that overlooked the Uria and Faria valleys. This proved to be a valuable observation point for the upcoming fighting in the mountains - the Japanese road was to come down the Faria Valley, and the famous Shaggy Ridge formed the western wall of the valley. In mid October the Australians gained their first foothold on the southern end of the ridge, before spending November attempting to improve their maps of the area and preparing for future operations.
The Japanese interfered with these plans by launching an attack of their own in the Ramu Valley (battle of Dumpu). This began on 8 December and the Japanese were able to push the Australians back a short distance. Their main effort came on the night of 12-13 December, but despite forcing the Australians to retreat just before dawn to avoid heavy losses, the Japanese had run out of steam, and the night attack was their last. Over the next few days they retreated back to their starting point, and the initiative returned to the Australians.
The Australians launched a major attack on 'The Pimple', the first in a series of four rocky outcroppings on the top of the ridge, on 27 December. The first and second 'pimples' were captured that day, and the third on the following day. The fourth and highest, which became known as McCaughey's Knoll, remained in Japanese hands. A Japanese counterattack on the afternoon of 28 December was repulsed, and the fighting then settled down into a period of artillery fire.
The situation on the Huon Peninsula changed on 2 January when American troops landed at Saidor, west of the Japanese base at Sio. General Adachi travelled to Sio by submarine, and decided to evacuate the survivors of the 21st and 50th Divisions from the Huon back to Madang. At the same time the troops on Shaggy Ridge were ordered to hold out long enough to allow the retreating troops to pass the northern end of the Bogadjim Road.
At the same time the Australian's were preparing to capture the watershed between the Faria and Mindjim Valleys. This would involve clearing the Japanese off the rest of Shaggy Ridge, as well as Faria Ridge to the east of the river and the Kankiryo Saddle at the end of the two valleys. They decided to carry out a three pronged assault using three battalions. One would attack up Shaggy Ridge and another would hit Faria Ridge from the east. The main attack would be carried out by the third battalion, which would advance up the valley on the western slopes of Shaggy Ridge and attack up Prothero 1, a high feature that overlooked the northern end of Shaggy Ridge and also Kankiryo Saddle. The main attack began on 20 January. By 23 January the Japanese had finally been cleared off Shaggy Ridge, and on the same day Kankiryo Saddle was captured. The Japanese still held on to Crater Hill, to the north-east of the saddle, and the Australians decided to pause for a few days to bombard this last position before risking an attack. An attack on 29 January was repulsed, but by 31 January the Japanese had begun to retreat, and on 1 February the Australians occupied Crater Hill.
During March the Australians advanced north across the Finisterre mountains towards Bogadjim. At the same time the Americans and Australians on the coast were pushing west. The two forces were slowly getting closer together. By the end of March the Japanese had withdrawn from their last major positions in the central mountains, and the Australians began to advance towards the coast. The first contact between the Finisterre and Huon forces came in mid-March when an American patrol ran into a long range Australian patrol.
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. By now the landings on the Admiralty Islands had made Madang untenable, and General Adachi decided to pull out and head for Wewak. The Australians made an unopposed entry into Madang on 24 April 1944, effectively ending the New Guinea phase of Operation Cartwheel. Two days earlier American forces had begun the next phase of the New Guinea campaign, landing at Aitape and Hollandia, west of Wewak (Operation Reckless). This meant that Adachi was now totally cut off on the north coast of New Guinea. In June-August 1944 he attempted to attack the American lines on the Driniumor River, east of Aitape, but this attack was repulsed. He then had to pull back to Wewak, where he was left in peace until the Australians took over at Aitape. By the end of the war Adachi had been forced into the mountains south of Wewak, and only a fragment of his army survived to surrender.