The Battle of the Coral Sea temporarily checked a direct seaborne invasion of Port Moresby on the southeastern coast of Papua. The Battle of Midway, whose magnitude of defeat the Japanese Imperial General Staff only publicly acknowledged in the beginning of July, made any seaborne threat to Port Moresby highly unlikely. With no air cover from the remaining Japanese carriers (the Zuikaku and Shokaku were still in port until mid-July, 1942), any invasion force would be at the mercy of land based bombers. Moreover, it was obvious MacArthur would attempt to build airfields on the north coast of Papua to extend their reach (He would. However, the never fully realized Operation Providence didn’t get out of the reconnaissance and security phase). For Lieut Gen Harukichi Hyakutake (we will hear his name again) the commander of the Japanese 17th Army in Rabaul, New Guinea and Papua needed to be secured by any means possible.

The Japanese decided to assess the feasibility of seizing Port Moresby by land. A Japanese reconnaissance pilot detected what he thought was a road connecting Port Moresby in the south with Buna on the north coast of Papua. However, the Kokoda Track was nothing but a slippery and sodden 60 mile trail that turned into a morass of deep mud whenever it rained, which was often. To complicate matters further, the Kokoda Track snaked over the Owen Stanley Range. The Owen Stanley Range is some of the harshest and most forbidding terrain on the planet: steep and tall mountains with jagged cliffs covered in dense jungle and moss covered upland swamps. Furthermore, he reported the Track as much wider than the overblown hiking trail it was. The staff of the Japanese 17th Army in Rabaul was skeptical of its the actual size, but there were no other options: the Japanese needed to secure Port Moresby as part of their outer perimeter. So Hyakutake requested the Japanese 4th Fleet land troops on northeastern Papua at Buna and Gona to secure a beachhead and recce the “road”.The defense of Port Moresby was the only reason preventing a Japanese invasion of northern Australia. And that the Kokoda Track was the only remaining way to get there was not lost on the Australians. This made Buna the next obvious Japanese target. 

On 25 June 1942, the newly formed Australian New Guinea Force launched Operation Maroubra (named after a Sydney suburb) to defend Buna, and prevent the Japanese from seizing the village of Kokoda and its airfield in the northern foothills of the Owen Stanley Range.

On 12 July, the Australian 39th Battalion of the 30th Brigade, a militia unit formed just after Pearl Harbor that so far spent the war as Port Moresby’s garrison, arrived in Kokoda after a grueling, if uncontested, two week march on the trail. With the Papuan Infantry Battalion at Buna, another militia unit with native Papuans and Australian officers, the 39th Battalion was referred to as the ad hoc “Maroubra Force” to distinguish them from other 30th Brigade units on the southern side of the Owen Stanley Range. They arrived none too soon.

On 21 July 1942, the Japanese launched Operation Ri, and landed the South Seas Force at Buna. The South Seas Force was a brigade sized naval landing force consisting of an infantry battalion, elite marine company, and an independent engineer regiment with native laborers from Rabaul. The Japanese commander, a well-connected lieutenant colonel, appropriated the engineers to act as infantry. Together, they quickly overwhelmed the reinforced Papuan battalion at Buna, and on the 25th broke through the 39th‘s defenses at the entrance to the Kokoda Track. Despite their men being used as infantry, the engineer officers surmised that it would take six porters to supply every soldier on the track. This was a ludicrous requirement even by the shoestring standards of Japanese logistics.in response, the aggressive and proud commander just had the engineers augment the native porters, and attacked south, determined to take Port Moresby.

With the loss of Buna and Kokoda, the Maroubra Force was not off to an auspicious start. But they came into their own in their dogged delaying actions and fierce counterattacks at bayonet point back down the Kokoda Track. The diggers made the Japanese pay dearly for every ridge and every blood soaked meter of trail. On 8 August, the 39th actually retook Kokoda briefly, and even buried their commander, who had been killed there the week before. When the Japanese landed, the rest of 30th Brigade began the march up the track and reinforced the 39th and the remaining Papuans. But the casualties were heavy, and the supplies over the track only came in trickles. The brigade commander was killed and the Maroubra Force fought on under the newly arrived but indomitable commander of the 39th, LieutCol Ralph Honner, with the other battalion also under their own junior officers. For over a month, the Japanese continually smashed into them with successive banzai charges, slowly pushing the Australians back. But the Japanese were suffering horrendous casualties, and in order to save face, Hyakutake was required to continually feed troops into the Kokoda Track. These troops were much needed on Guadalcanal where American Marines had landed on 7 August.

About the time the Marines were hanging on to Henderson Field by their fingernails, the Australian 21st Brigade of the veteran 7th Division arrived and its commander, Brigadier Arnold Potts, assumed command of the Maroubra Force and the remnants of 30th Brigade. The 21st was a regular formation with extensive experience in the Western Desert and fighting in Syria and Lebanon. They had no jungle training or experience, but they quickly learned from the 30th Brigade troops – grizzled veterans after a month on the Track. 

In punishing conditions that Allied medical professionals would study to determine how long a human being can survive on the line in the jungle before they’re permanently broken (three months), Potts and the Maroubra Force slowly fell back and bled the Japanese. For another month, the Japanese threw troops down the Kokoda Trail in an ever lengthening supply line and sledgehammered the Australian positions. However, as Japanese strength grew, these banzai charges were just fixing attacks that supported flanking columns which attempted to “trail block” the Australians until they withdrew. (The same technique worked very well against the British in Burma). But the Japanese focus on getting combat troops into the fight on the Kokoda Track meant there was little throughput for logistics. For example, the Japanese engineers were thrown into the fight as infantry before they could actually do what they were meant to do, turn Buna and Gona into a proper port and improve the Track. Many Japanese units were unsupported and withering away.

The Japanese were literally sacrificing the lives of their soldiers by assaulting the Australian positions before they starved to death. The problem for Brigadier Potts was it was actually working.

Maroubra Force was in close contact with the Japanese for all of August and most of September. At no point in time were the nearest Japanese farther than 30 meters from the Potts’ main line of resistance. There was at least a platoon passage of lines to the rear under heavy pressure every day. To exasperate the Japanese supply situation, Potts’ established “Chaforce” and “ Honnerforce”, both about 400 man ad hoc task forces, to raid the Kokoda Track to the north. Nonetheless, the Japanese still came on.

MacArthur and some armchair strategists in Australia were concerned with the Japanese advance, and several Australian officers were sacked, fueled by wild tales of panicked abandon of positions. But they failed to grasp the extreme conditions on the Kokoda Trail: the heat, humidity, the thickness of the vegetation, disease, even the cold at the higher elevations. Furthermore, they failed to even acknowledge the lengths the Japanese were willing to go to maintain an overwhelming superiority in numbers, which never dropped below four to one.

While the Japanese advance continued, the Australian buildup at Port Moresby was slowly gaining momentum. The rest of the Australian 7th Division arrived, and on 7 September the indefatigable 39th Battalion was withdrawn from the line. Of the 800 men that started up the trail two months before, just 30 remained. 

But what cannot continue indefinitely, eventually will not. Just as the fighting on the Kokoda Track relieved pressure on the US Marines on Guadalcanal, the reverse was true in September: The losses suffered by the Japanese in the Solomon’s forced Hyakutake to suspend operations on New Guinea until “the Guadalcanal matter was resolved”.

Maroubra Force held, despite the Japanese within sight of Port Moresby.

In mid-September, Potts turned over the Maroubra Force to the commander of the recently arrived 25th Brigade, who withdrew to Imita Ridge, the last effective natural barrier before Port Moresby. Despite Hyakutake’s orders, the Japanese tried one last push before they moved into defensive positions. They failed.

After a brief respite, it was time to do it all over again, but this time in reverse. In late September, after it was obvious the Japanese suspended the offensive, the Australians began attacking back up the Kokoda Track. For the first time in the Pacific War, the Japanese were on the operational defensive.

The Japanese would prove as tenacious in the defense, as they were aggressive and courageous on the attack.