Markham, Ramu and Finisterre campaigns

During September 1943, Australian forces from Major General George Vasey's 7th Division, advancing from Nadzab, had captured Lae, as part of a pincer undertaken in conjunction with Major General George Wootten's 9th Division, which had advanced along the coast from the east of Lae. Heavy rain had held up the Australian advance and much of the garrison had managed to withdraw inland, prior to the capture of the town. To follow these forces up, the 9th Division's focus then shifted to the Huon Peninsula, while the 7th Division – following the capture of Kaiapit – advanced from there to Dumpu and Marawasa, to prepare for the Australian advance through the Ramu Valley and into the Finisterre Range, towards Bogadjim near Madang on the northern coast.[1][2]

The Japanese formation in the campaign was the Nakai Detachment, a brigade-sized formation detached from the Japanese 20th Division under Major General Masutaro Nakai.[3] The area was defended by several battalions of the 78th Infantry Regiment, supported by the 26th Artillery Regiment and the 27th Independent Engineer Regiment. The II/78th and two companies of the III/78th were deployed forward around Kankiryo and Shaggy Ridge, with the I/78th spread out around Saipa and Yokopi and the remaining two companies of the III/78th at Yaula, the 239th Infantry Regiment held the rear around Madang, Erima and Bogadjim, along with 2,000 unassigned reinforcements; this was a force of about 12,000 men.[1] It faced the Australian 7th Division, consisting of approximately 17,000 men,[4] under Vasey, and made up of the 18th, 21st and 25th Brigades, along with the 2/6th Commando Squadron.[5]

Markham and Ramu Valley Operations, September–November 1943

The campaign began in September 1943 following the 7th Division's drive on Lae, as part of the wider New Guinea campaign, which saw the 9th Division carrying out operations along the Huon Peninsula on the coast to the east, while the 7th moved towards the west.[6] Carrying out a number of smaller-scale operations, the units of the 21st and 25th Brigades advanced up the Markham and Ramu Valleys. Apart from a significant engagement around Kaiapit, where the 2/6th Commando Squadron captured the village and killed over 200 Japanese. The Australians were barely resisted as they advanced and they arrived in Dumpu in early October. During the entire advance, the Australian and American forces in the Ramu Valley were supplied by air. The capture of the Ramu Valley, allowed a forward airbase to be developed at Gusap.[5][7][8]

Following this, the 7th Division provided security for a number of airfields that were constructed in the territory they had captured in the valleys.[9] To assist with this, the 6th Machine Gun Battalion was brought up from Port Moresby to defend Gusap.[10] However, the Japanese remained in strong possession of the Finisterre Range, and their positions at Kankiryo Saddle north of the Ramu river and the 1,500 m (4,900 ft) high razorback ridge named Shaggy Ridge, continued to threaten the airfields.[7] 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.[5][7]

Thus, the Kankiryo Saddle and Shaggy Ridge were of vital strategic importance for both the Japanese and the Australians. For the Japanese, it provided a strong obstacle to the Australian advance north towards 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 signalled threat and their commander, Vasey, came to the decision that he would have to launch an offensive in order to capture this ground.[7]

Troops of the 2/16th Infantry Battalion, watch aircraft bombarding The Pimple prior to their attack on Japanese positions there, 27 December 1943.

This led to a number of battles in the steep mountains of the Finnisterres. In October, battles took place at Palliser's Hill,[11] and then later at Johns' Knoll where the Australians first managed to capture the knoll and then held it against a determined Japanese counterattack.[5] In November, the 25th Brigade relieved the 21st as the offensive was maintained,[7] and later in December and into January heavy fighting took place around Shaggy Ridge,[5] a 6.5-kilometre (4.0 mi) long spur dotted by several rocky outcrops. The Japanese had established numerous strong posts and positions along the ridge, blocking the Australian advance towards the coast, where they were aiming to secure Bogadjim and Madang.[12] 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, which commanded the southern half of the position and had prevented the Australians advancing over the previous two months. These preparatory fires were followed by an assault up the steep slopes of The Pimple by the 2/16th Infantry Battalion, which employed ladders made out of bamboo to help scale the face of the slope. Held up overnight by a Japanese pillbox, the 2/16th resorted to explosives to destroy it.[12][13]

Early in the new year, the 15th and 18th Brigades relieved the 21st and 25th Brigades around Shaggy Ridge, and planning for a new offensive began.[12] The major Australian attack on Shaggy Ridge – codenamed Operation Cutthroat – was launched by the 18th Brigade on 19–20 January.[14] The 2/4th Field Regiment, which established its guns around the Lake area to the west of the Mosia River, and south of Guy's Post, while stores were brought up to that position by jeep.[15] The brigade's three battalions were to converge on the Kankiryo Saddle from three different directions: the 2/12th Infantry Battalion was to advance from Canning's Saddle, east of Shaggy Ridge, and attack two well-defended knolls on the northern end of Shaggy Ridge, known as Prothero I and II; the 2/9th Infantry Battalion would attack northwards along Shaggy Ridge itself, to take McCaughey's Knoll, by way of Green Sniper's Pimple; and the 2/10th Infantry Battalion would advance along Faria Ridge, which lay to the east of Shaggy Ridge and joined it at Kankiryo Saddle.[16]

After the Kankiryo Saddle was secured on 26 January 1944, the Japanese withdrew to Crater Hill. From there, they had good observation of the saddle to the south-west, and they established a strong position. The Australians surrounded the position and over the course of a week reduced the position with patrolling and air attacks, forcing the Japanese defenders to abandon the position on 31 January 1944, 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.[17]

Shortly after Shaggy Ridge was captured, the 18th Brigade was replaced by the 15th Brigade, a Militia formation.[18] As the Australians began consolidating their position, the 7th Division was ordered to limit its exploitation, while supplies were pushed forward of Kankiryo. Meanwhile, in an effort to harass the Japanese rearguard, the 57th/60th Infantry Battalion undertook a program of long range patrols to the north. A landing by two US battalions around the Yalau Plantation pushed the Japanese further back, but nevertheless, their rearguards continued to provide determined resistance and the Australians advanced towards Bogadjim, pursuing the Japanese forces as they withdrew.[19]

Members of "B" Company, Australian 2/12th Battalion, who helped silence a Japanese mountain gun on one of the hills known as Prothero I & II, 22 January 22, 1944.

Yaula was captured on 4 April linking up with elements of the 2/2nd Commando Squadron. A few days later, the 11th Division, under the command of Major General Allan Boase took over from the 7th, and they subsequently linked up 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 troops from the 8th Brigade came ashore there, effecting a link up between the 5th Division,[12] which had been advancing along the coast from Saidor, which had been secured by US and Australian forces in January – February 1944. Madang was subsequently taken on 24–25 April by troops from the 8th and 15th Brigades, while the 30th Infantry Battalion secured Alexishafen the following day.[20] A follow-up landing was made by the 37th/52nd Infantry Battalion on Karkar Island, while the 35th Infantry Battalion secured a large quantity of abandoned Japanese stores at Hansa Bay, and pushed patrols towards the Sepik River.[12]