The Battle of Ioribaiwa

The final great defensive battle fought by the Australians in the Kokoda Campaign was fought on Ioribaiwa Ridge, just 40 kilometres from and within sight of Port Moresby. It marked the end of the Japanese surge southwards and their final victory in the Kokoda Campaign.

Ioribaiwa was the first battle for Brigadier Ken Eather who replaced Brigadier Arnold Potts as Commander of Maroubra Force. Brigadier Potts had been sacked after the disastrous defeat at the Battle of Brigade Hill. Ioribaiwa also marked the first action of the Campaign for the 25th Brigade and the 3rd Militia Battalion, who had been brought forward to reinforce the battered 2/14th and 2/16th Battalions (the remnants of which had been merged into a composite battalion following heavy losses in the Campaign). 

Brigadier Eather, like Potts before him, assumed that the force that he opposed was much larger than the two battalions it actually was. The Nankai Shitai (South Seas Force) was led by Colonel Masao Kusonose in this battle. Riddled with malaria, he was forced to conduct the battle from his sick bed and was initially unaware that the Australians had been significantly reinforced. 

Prior to the battle, both forces were preparing for attack. Eather, well aware of the aggressive intent of his superiors, was marshalling his forces ready for an offensive when the Japanese beat him to the punch. Kusonose hoped to replicate the same tactics that had worked for him at Brigade Hill. With half of the 3/144th (ie. 3rd Battalion, 144th Regiment) he attacked the Australian forward positions and unleashed the full complement of his artillery battery. Meanwhile, he sent the 2/144th to the west of the ridge in an attempt to flank the Australians and pierce their rear defences. In reserve he held the second half of the 3/144th. 

Forced to swap from an offensive to a defensive posture, Eather had four of his five battalions in a line stretching across Ioribaiwa Ridge. From left to right he assembled his units thus: the 2/31st Infantry Battalion, the composite battalion, the 3rd Infantry Battalion and the 2/33rd Infantry Battalion. Behind these positions was his reserve battalion – the 2/25th. The brunt of the Japanese frontal attack and firepower was brought to bear on the beleaguered composite battalion. 

With the Japanese making inroads into the forward pockets of the Australian defences, the 2/144th was also making headway to the left hand side of the Australian positions. It was here that they encountered the 2/31st who were in turn attempting to manoeuvre into a position to do exactly the same thing to the Japanese. A game of ‘cat and mouse’ ensued as these two battalions sparred and spent the remainder of the battle attempting to flank one another without either gaining a decisive advantage. 

With his attempts to flank on the west side of the battlefield checked and his depleted half battalion struggling to smash the Australians head-on, Kusonose ordered his reserve half battalion to attempt to encircle the Australians’ eastern flank. This operation was carried out, though the Japanese underestimated the length of the Australian defensive lines and drove their attack between the 3rd Battalion and 2/33rd Battalion’s positions. Although this thrust made an instant cleft in the 3rd Battalion's positions, the Australians steadied and held the Japanese at bay. 

Two Australian counter-attacks were launched to expel the Japanese. The first, by the 2/25th was repelled, while the second, by the 2/33rd, failed to even locate the Japanese positions. This serves to reinforce the density of the jungle and illustrates the difficulties that both sides had throughout the Campaign in moving sizeable forces on the battlefield when not on the Trail. 

With headway not being made elsewhere, the Japanese in the east were finally able to capture the high point on Ioribaiwa Ridge which afforded them views along the entire Australian position. This, along with the constant toll that the Japanese artillery was causing, prompted Eather to signal Major General Allen for permission to pull his troops back to Imita Ridge. Allen consented but warned that no further retreat would be sanctioned. He said, “There won't be any withdrawal from the Imita position, Ken. You'll die there if necessary.” As such, the Australians conducted a successful withdrawal to Imita and ceded the battlefield to the surprised Japanese. 

Thus, Iorabaiwa saw the wearied Japanese secure their final victory in the Kokoda Campaign against a force superior in numbers. Arguments over the respective sizes of each force has led to contention as to whether or not Eather should have remained on Iorabaiwa Ridge. Before the retreat, Kusonose was worried that his soldiers had been unable to force a breakthrough. By contrast, Eather, with the 2/25th, still had a fresh battalion in reserve to attack an enemy who had already expended their reserves. Eather reasoned that withdrawing to Imita would allow the Australians to respond to Japanese artillery with their own artillery for the first time in the campaign. In addition, it would shorten the Australian supply lines, further providing a better defensive position. 

Irrespective of the conjecture, the joy of the victorious Japanese was short-lived. They had reached the zenith of their advance and an enormous supply crisis of their own loomed. The Australian forces that were able to scramble to Imita would soon push north again and drive the Japanese from the Owen Stanley Ranges. 

Nick Anderson 
Australian Army History Unit 

Last updated
4 December 2016