The 'Campaign for the Finisterre Mountain Range' was fought between Allied and Japanese forces in the Markham river valley, Ramu river valley and Finisterre mountain range in the aftermath of the 'Campaign for Eastern New Guinea' (19 September 1943/24 April 1944).

During the campaign, Australian ground forces were supported by Australian and US aircraft in an advance through the Markham river valley and Ramu river valley during which there were minor clashes with Japanese forces, which withdrew towards their main defensive line in the Finisterre mountain range. Central to the geographical and strategic natures of this campaign was the imposing 'Shaggy Ridge', running north/south in the Finisterre mountain range: this was the scene of a decisive battle during which the Australians assaulted the Japanese positions in December 1943 and January 1944. Following the fighting around 'Shaggy Ridge', the Japanese withdrew toward the northern coast of New Guinea, where they were pursued by Australian and US forces advancing through the Finisterre mountain range and along the coast from Saidor. Following the capture of Madang, the Japanese eventually withdrew to Wewak where further fighting took place in 1944 and 1945.

During September 1943, forces of Major General G. A. Vasey’s Australian 7^th Division, advancing from Nadzab, had captured Lae as part of a pincer undertaken in conjunction with Major General G. F. Wootten’s Australian 9^th Division, which had advanced along the coast from the east of Lae. Heavy rain had slowed the Australian advance and much of the Japanese garrison had managed to withdraw inland before the town’s capture. To follow the Japanese retirement, the Australian 9^th Division’s focus then shifted to the Huon peninsula, while the Australian 7^th Division, following the capture of Kaiapit, advanced from there to Dumpu and Marawasa to prepare for the Australian advance through the Ramu river valley and into the Finisterre mountain range, toward Bogadjim near Madang on the northern coast.

The Japanese force involved in the campaign was Major General Masutaru Nakai’s 'Nakai' Detachment, a brigade-sized formation detached from Lieutenant General Shigemasa Aoki’s Japanese 20^th Division. The area was defended by several battalions of the 78^th Regiment, supported by the 26^th Artillery Regiment and the 27^th Independent Engineer Regiment. The 2/78^th Regiment and two companies of the 3/78^th Regiment were deployed forward around Kankiryo and 'Shaggy Ridge', with the 1/78^th Regiment deployed around Saipa and Yokopi and the remaining two companies of the 3/78^th Regiment at Yaula, the 239^th Regiment held the rear around Madang, Erima and Bogadjim, together with 2,000 unassigned reinforcements. The Japanese force numbered some 12,000 men. It faced the Australian 7^th Division, comprising about 17,000 men of the 18^th, 21^st and 25^th Brigades, along with the 2/6^th Commando Squadron.

The campaign began in September 1943 following the Australian 7^th Division’s drive on Lae, as part of the wider New Guinea campaign, which saw the Australian 9^th Division carrying out operations along the Huon peninsula on the coast to the east, while the Australian 7^th Division moved toward the west. Carrying out a number of smaller-scale operations, the units of Brigadier I. N. Dougherty’s 21^st Brigade and Brigadier K. W. Eather’s 25^th Brigade advanced up the Markham and Ramu river valleys. Apart from a significant engagement around Kaiapit, where the 2/6^th Commando Squadron captured the village and killed over 200 Japanese, the Australians were barely resisted as they advanced, and arrived in Dumpu early in October. During the entire advance, the Australian and US forces in the Ramu river valley were supplied by air. The capture of the Ramu river valley allowed a forward air base to be developed at Gusap.

Following this, the Australian 7^th Division provided security for a number of the airfields which were constructed in the territory they had captured in the valleys. To assist in this task, the 6^th Machine Gun Battalion was brought up from Port Moresby to defend Gusap. However, the Japanese remained in strong possession of the Finisterre mountain range, and their positions at Kankiryo Saddle, to the north of the Ramu river, and on the 4,900-ft (1495-m) razorback ridge nicknamed 'Shaggy Ridge' continued to threaten the airfields. This threat manifested itself in the road that the Japanese were attempting to build from Madang on the coast inland to Nadzab, via Bogadjim, along which they were hoping to advance through to Dumpu.

Thus, the Kankiryo Saddle and 'Shaggy Ridge' were of vital strategic importance for both the Japanese and the Australians. For the Japanese, these features provided a strong obstacle to the Australian advance to the north in the direction of the coast, while also offering them the ground along which they could launch their own offensive in order to recapture the territory they had lost earlier in the campaign. For the Australians, the Japanese positions on the high ground implied a major threat and their commander, Vasey, came to the decision that he would have to launch an offensive in order to capture this ground.

This led to a number of battles in the steep elevations of the Finisterre mountain range. In October, battles took place at Palliser’s Hill and then later at Johns' Knoll, where the Australians first managed to capture the knoll and then held it against a determined Japanese counterattack. In November, the 25^th Brigade relieved the 21^st Brigade as the offensive was maintained, and from a time later in December into January heavy fighting took place around 'Shaggy Ridge', a 4-mile (6.4-km) spur dotted with several rocky outcrops. The Japanese had established numerous strongposts and positions along the ridge, and these blocked the Australian line of advance toward the coast, where they were aiming to secure Bogadjim and Madang. The initial attacks on 'Shaggy Ridge' began on 27 December with a heavy artillery and air preparation of the Japanese positions around 'The Pimple', a steep rocky outcrop commanding the southern half of the position and which had prevented the Australian advance over the previous two months. These preparations were followed by an assault up the steep slopes of 'The Pimple' by the 2/16^th Battalion, which employed ladders made out of bamboo to help scale the face of the slope. Held up overnight by a Japanese pillbox, the 2/16^th Battalion resorted to the use of explosives to destroy the pillbox.

Early in the new year, Brigadier H. H. Hammer’s 15^th Brigade and Brigadier F. O. Chilton’s 18^th Brigade relieved the 21^st Brigade and 25^th Brigade around 'Shaggy Ridge', and planning for a new offensive began. The major 'Cutthroat' (i) Australian attack on 'Shaggy Ridge' was launched by the 18^th Brigade on 19/20 January. The 2/4^th Field Regiment, had established its guns around the lake area to the west of the Mosia river and to the south of Guy’s Post, while stores were brought up to that position by Jeep. The brigade’s three battalions were to converge on the Kankiryo Saddle from three different directions: the 2/12^th Battalion was to advance from Canning’s Saddle, to the east of 'Shaggy Ridge', and attack two well-defended knolls on the northern end of 'Shaggy Ridge', known as Prothero I and Prothero II; the 2/9^th Battalion was to attack to the north along 'Shaggy Ridge' itself to take McCaughey’s Knoll by way of Green Sniper’s Pimple; and the 2/10^th Battalion was to advance along Faria Ridge, which lies to the east of 'Shaggy Ridge' and joins it at the Kankiryo Saddle.

After the Kankiryo Saddle had been secured by the Australians on 26 January 1944, the Japanese withdrew to Crater Hill, from which they had good observation of the saddle to the south-west, and now established a strong position. The Australians surrounded the position and, over the course of a week’s fighting, reduced the position with patrols and air attacks, forcing the Japanese to abandon the position on 31 January and fall back to Paipa. Casualties during the fighting to secure 'Shaggy Ridge' amounted to up to 500 Japanese killed, and 46 killed and 147 wounded for the Australians.

Shortly after 'Shaggy Ridge' had been captured, the 18^th Brigade was replaced by the 15^th Brigade, a militia unit. As the Australians began consolidating their position, the 7^th Division was ordered to limit its exploitation, while supplies were pushed forward of Kankiryo. Meanwhile, in an effort to harass the Japanese rearguard, the 57^th/60^th Battalion undertook a programme of long-range patrols to the north. A landing by two US battalions around the Yalau Plantation pushed the Japanese farther back, but their rearguards nevertheless continued to provide determined resistance as the Australians advanced toward Bogadjim in their pursuit of the Japanese forces as they withdrew.

Yalau was captured on 4 April, allowing the advancing force to link with elements of the 2/2^nd Commando Squadron. A few days later, Major General A. J. Boase’s Australian 11^th Division took over from the Australian 7^th Division and subsequently linked with US forces on the coast around Rimba as they pushed forward along an axis bounded by the Kabenau and Nuru rivers. Bogadjim was reached on 13 April, and on 23 April units of Brigadier C. E. Cameron’s Australian 8^th Brigade came ashore there, creating a link between Major General A. H. Ramsay’s Australian 5^th Division, which had been advancing along the coast from Saidor, itself secured by US and Australian forces in 'Dexterity' during January and February 1944. Madang was subsequently taken on 24/25 April by troops from the 8^th Brigade and 15^th Brigade, while the 30^th Battalion secured Alexishafen on the following day. A follow-up landing was made by the 37^th/52^nd Battalion on Karkar island, while the 35^th Battalion secured a large quantity of abandoned Japanese stores at Hansa Bay, and pushed patrols towards the Sepik river.

For the Australians, the advance through the Markham, Ramu and Faria river valleys had proved to be both lengthy and arduous. The casualties of the Australian 7^th Division between 18 September 1943 and 8 April 1944 amounted to 204 men killed and 464 wounded. Disease took an even greater toll, no fewer than 13,576 men being evacuated. Japanese estimates of their own casualties indicate losses of 800 men killed, 400 wounded and 800 dead from disease.

With the capture of Madang, the Allies had finally secured the Huon peninsula. Even so, the Allies were unable to prevent the Japanese defenders from withdrawing and, as a result, they were unsuccessful in completely destroying them. Following the fall of Madang, the remnants of the Japanese 18^th Army eventually withdrew to the Wewak area with the intention of falling back to Hollandia. That base fell before they could arrive after the Allies had launched the 'Reckless' and 'Persecution' operations, and consequently the Japanese remained in the Wewak area. US forces of Major General Horace H. Fuller’s 41^st Division subsequently landed at Aitape, and in mid- to late 1944, US and Japanese forces clashed in the 'Battle of the Driniumor River'. Late in 1944, Major General J. A. S. Stevens’s Australian 6^th Division arrived to relieve the US garrison, and the Australian forces subsequently launched the 'Campaign for Aitape and Wewak' to secure the airfield and then clear the Japanese from the inland areas patrolling through the Torricelli and Prince Alexander mountain ranges.