The Markham Valley, Ramu Valley and Finisterre Range campaigns were a series of battles within the broader New Guinea campaign of World War II. The campaigns began with an Allied offensive in the Ramu Valley, from 19 September 1943, and concluded when Allied troops entered Madang on 24 April 1944. During the campaign, Australian forces – supported by Australian and US aircraft – advanced through the Markham Valley and Ramu Valleys during which there were minor clashes with Japanese forces, which withdrew towards their main defensive line in the Finisterre Range.
A central geographical and strategic feature of these campaigns was the imposing Shaggy Ridge, running north–south in the Finisterres; this was the scene of a climactic battle during which the Australians assaulted the Japanese positions in December 1943 and January 1944. Following the fighting around Shaggy Ridge, the Japanese withdrew towards the northern coast of New Guinea, where they were pursued by Australian and US forces advancing through the Finisterres 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.
Background
Strategic situation
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.
Opposing forces
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. 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. It faced the Australian 7th Division, consisting of approximately 17,000 men, under Vasey, and made up of the 18th, 21st and 25th Brigades, along with the 2/6th Commando Squadron.
Campaign
Advance into the Markham and Ramu Valleys
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. 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.
Following this, the 7th Division provided security for a number of airfields that were constructed in the territory they had captured in the valleys. To assist with this, the 6th Machine Gun Battalion was brought up from Port Moresby to defend Gusap. However, the Japanese remained in strong possession of the Finisterre Range, and their positions at Kankiryo Saddle north of the Ramu river and the high razorback ridge named 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.