'Maroubra' was the Allied designation of the elements of Major General George A. Vasey’s Australian 7^th Division involved in the Kokoda Trail and later operations against Major General Tomitaro Horii’s South Seas Detachment in New Guinea after the launch of the Japanese 'Ri' (September 1942/July 1943).

'Maroubra' Force was thus the name given to the Australian infantry force which defended Port Moresby on the south coast of Papua, at the eastern end of New Guinea island, from the Japanese overland advance across the Own Stanley mountains in the Kokoda Trail (or Track) campaign of the Pacific war. 'Maroubra' Force was one of the many units constituting the body of the New Guinea Force, the main Allied army formation in the South-West Pacific Area during 1942. Formed on 21 June 1942, it comprised the Papuan Infantry Battalion, 39^th Battalion and the 53^rd Battalion and was under the command of Major General Basil M. Morris.

In the middle of 1942, the 39^th Battalion, previously the garrison force around Port Moresby, was sent overland via the Kokoda Trail to secure the Buna area on the north-east coast in 'Providence' and to prepare to oppose any Japanese advance. The Papuan Infantry Battalion of about 280 Papuan troops with Australian officers, was already to the north of the Owen Stanley mountains at the northern end of the Kokoda Trail. On 21 July, the Japanese landed on the north-east coast in 'Ri' and overwhelmed the Papuan Infantry Battalion, and took the start of the Kokoda Trail.

The 'Maroubra' Force then fought a successful month-long delaying action through the debilitating terrain of the Owen Stanley mountains before being reinforced and finally driving off the Japanese just outside of Port Moresby. The 'Maroubra' Force was relieved by the 16^th Brigade and 25^th Brigade, which undertook the subsequent counter-offensive which drove the Japanese back to their beach-heads at Buna, Gona and Sanananda on the north-east coast of Papua. At the Battle of Buna-Gona in November 1942/January 1943, the 'Maroubra' Force in turn relieved the 18^th Brigade and 25^th Brigade besieging Gona, and successfully crushed the Japanese beach-head there.

The 'Maroubra' Force was commanded initially by Brigadier Selwyn H. W. G. Porter of the 30^th Brigade, then Lieutenant Colonel H. Ralph Honner of the 39^th Battalion and finally Brigadier Arnold W. Potts of the 21^st Brigade, who was later relieved of his command in controversial circumstances.

At its peak, the 'Maroubra' Force comprised the 39^th Battalion, the 53^rd Battalion, and the 21^st Brigade (2/14^th, 2/16^th and 2/27^th Battalions). The 53^rd Militia Battalion also saw brief action during the Battle of Isurava, but was defeated and subsequently withdrew, greatly demoralised, especially after its commanding officer and many of its senior officers had been killed in action.

The Kokoda and Buna-Gona battles took a heavy toll on the soldiers of the 'Maroubra' Force. As an example, following both battles the 39^th Battalion mustered barely 30 survivors (from a nominal strength of between 600 and 800), the remainder being dead, missing, wounded, or in hospital in Port Moresby and northern Australia suffering from disease and exhaustion. The 'Maroubra' Force, Honner and Potts were instrumental in the successful defence of south-western Papua as the outlying northern bastion of Australia.

The Kokoda Trail campaign began with a serious failure of Japanese intelligence following the Battle of the Coral Sea in May 1942. The Japanese had previously captured a book in Manila, the capital of the Philippine islands group, containing a vague, second-hand account of a road linking Buna and Port Moresby. Aerial reconnaissance then showed that there was a road from Buna on the coast to Kokoda on the high point of the Owen Stanley mountains, and that this road continued to the edge of the thick jungle. Based on the vague references in the Manila book, Japanese intelligence concluded that the road in fact continued toward Port Moresby under the jungle canopy, a conclusion which appeared to be confirmed by a second aerial observer who thought he saw a serviceable road from Kokoda to Isurava. What the Japanese failed to take into account, however, was that the observer was at the time attempting to evade Allied fighter cover, and therefore wholly misjudged the width and condition of the trail.

Based on this intelligence, which was both inadequate and indeed erroneous, on 1 July 1942 Imperial General Headquarters ordered Horii’s South Seas Detachment to land a force near Buna on 21 July 1942 and secure a beach-head. The initial landings were effected by the Yokoyama Advance Party, a force of about 2,000 engineers of the 15^th Independent Engineer Regiment covered by a infantry battalion of the 144^th Regiment and one company of the 1^st Sasebo Special Naval Landing Force. The landing force was under orders to advance to the foothills of the Owen Stanley mountains and evaluate the road and river communications as to their suitability for supporting an attack across the mountains. Horii himself was sceptical, and his chief-of-staff had calculated that the Japanese would have to collect a force of at least 32,000 porters to support a combat force of 5,000 men at the Port Moresby end of the Kokoda Trail.

On 15 July, however, Lieutenant Colonel Masanobu Tsuji arrived at the headquarters of Lieutenant General Haruyoshi Hyakutake’s 17^th Army at Davao in the Philippine islands group with orders for the relocation of this army to Rabaul on New Britain island and for the South Seas Detachment to begin an immediate advance from Buna to Port Moresby, without waiting for the completion of the feasibility study. The source of Tsuji’s authorisation remains obscure: Tsuji claimed imperial sanction, but on 25 July a telegram from the operations section in Tokyo revealed that the Imperial General Headquarters was still awaiting the results of the feasibility study before ordering an advance across the mountains. Tsuji had exceeded his instructions, which were to await the feasibility report at Davao and then join in making a decision.

With elements of the South Seas Detachment already landed and in combat with the Australians, however, Hyakutake feared losing face, and reported that the advance on Port Moresby was feasible and the offensive should proceed. Prisoner of war interrogations suggesting that there were already 20,000 Australian troops at Port Moresby were ignored.

As noted above, the Yokoyama Advance Party had carried out its landing on 21 July as scheduled, though the 9,788-ton transport Ayatosan Maru was sunk by Allied aircraft and the 5,974-ton transport Ryoyo Maru was forced to return to Rabaul before unloading its cargo of horses. The troops also brought hundreds of bicycles with them, which were quickly abandoned. Horii’s troops began working their way up the Kokoda Trail the next day, making contact with the forward elements of the 39^th Battalion on 23 July at Awala. Within four days, the defenders had been pushed back to Kokoda village. The town and airstrip fell on 29 July, leaving the Australians with no way to deliver reinforcements by air.

The next two months saw the Japanese force, reinforced by the remainder of the South Seas Detachment and the 41^st Regiment from Malaya, drive the Australians back over the Owen Stanley mountains and to within 30 miles (48 km) of Port Moresby.

The Australians delayed the Japanese advance at Isurava for five crucial days before being driven back on 30 August. The senior Allied commanders then expected the Australians to make a stand at 'The Gap', the summit pass along the track, which they seemed to think was a narrow and easily defensible defile. In fact, 'The Gap' is a broad depression in the summit ridge 7 miles (11 km) wide, and the Australians made no attempt to hold here, and the Japanese were able to cross onto the southern slopes of the Owen Stanley mountains almost unopposed.

Reinforced by two brigades from the 7^th Division, the Australians prepared to make their stand on Imita Ridge, the last geographical obstacle to the north-east of Port Moresby. However, by 7 September the Japanese 'Re' attempt to land at Milne Bay to the south-east had failed, so removing the other element of the Japanese two-pronged drive on Port Moresby, and by 14 September the Japanese drive along the Kokoda Trail had lost its momentum. The reverses which their forces suffered at about the same time on Guadalcanal in the Solomon islands group after 'Watchtower' now persuaded the Japanese high command to order its troops in Papua to fall back to the Owen Stanley mountains, prepare defensive positions and await developments.

On 23 September the Australians went over to the offensive, and by 27 September the Japanese were in full retreat. Japanese veterans of the Kokoda Trail campaign claimed that the South Seas Detachment had not trained in the tactics of retreat, for such a retrograde movement was considered shameful, and this clearly played a part in turning the retreat of the South Sea Detachment into a rout. Conditions became so bad that some of the starving Japanese soldiers resorted to cannibalism of dead Australians.

On 6 October elements of Major General Edwin F. Harding’s US 32^nd Division began moving over the Kapa Kapa trail toward Buna, but the trail was so difficult that the US troops were left in no condition to fight. On 17 October there began the airlift of an entire regiment of the 32^nd Division from Port Moresby to Wanigela to join the offensive.

The Australians retook Kokoda on 2 November, and with resupply via the airstrip at Kokoda once again possible, the Australian drive accelerated. On 10 November Horii himself was cut off by the 25^th Brigade, and drowned about 10 days later while attempting to rejoin his troops along the coast by canoe.

By 19 November the Allies were closing on the Japanese beach-heads in the Buna area.