Involving forces from Australia, New Zealand and Japan, the battle was part of the wider Bougainville campaign, which had begun in late 1943 and lasted until the end of the war in August 1945.

Over the next two days several unsuccessful rescue attempts were made until eventually, in the early morning of 11 June, the last Australian survivors were picked up.

As a result, shortly afterwards the Australian forces on Bougainville changed the focus of their operations to the southern sector of the island where they were able to advance along the coastal plain towards the main Japanese position at Buin.

[4] US Marines conducted an amphibious landing at Cape Torokina, on the western coast of the island, north of Empress Augusta Bay, in November 1943.

After an initial counter-attack which had been repulsed, the US Marines had been replaced by a garrison of US Army troops who began consolidating their position around Torokina, establishing a strong perimeter.

[7] Although Japanese forces on Bougainville actually numbered around 40,000 men at the time,[8] Allied intelligence failed to determine this accurately, estimating that there were only about 17,500 defenders.

[9][10] The majority of the Japanese force was believed to be concentrated in the south and as a result the main effort of the Australian plan was focused upon driving towards Buin.

In the north, it was planned that the Japanese would be forced into the narrow Bonis Peninsula and contained there while, in the centre, the seizure of Pearl Ridge would give the Australians control of the east–west avenues of approach, as well as affording them protection against further counter-attacks and opening the way for a drive to the east coast.

[18][19] In April, the 26th was relieved by the 55th/53rd Infantry Battalion which advanced north to Ratsua,[Note 3] from where the Australians planned to move along the Bonis Peninsula.

[22] Australian intelligence suggested that the Japanese had concentrated strongly along the approaches to the peninsula, and in order to deal with these positions it was decided that an amphibious landing would be made by a company of the 31st/51st Infantry Battalion near the jetties around Porton Plantation, 3.1 miles (5.0 km) to the north of Ratusa,[21] to outflank them and launch an attack from the rear, while the main force – consisting of the remainder of the 31st/51st and the 26th Infantry Battalion – pushed north from the Ratsua front to establish a new position along a line between Porton and Chindawon.

[32][33] The Japanese force was commanded by the senior naval officer at Buka, Captain Eikichi Kato,[34] whose 87th Naval Garrison Force had taken over responsibility for the defence of the Tarlena area[Note 4] when the Imperial Japanese Army's 38th Independent Mixed Brigade was transferred south to the Numa Numa area.

They came ashore unopposed and after advancing about 100 yards (91 m) inland established a small perimeter around the beachhead in the tree line surrounding the plantation.

[38][39] Lacking organic indirect fire support as all the mortars had been in the landing craft that were in the second wave,[39] Downs established communications with the artillery, and a barrage was brought down on suspected Japanese positions by the artillery forward observation officer, Lieutenant David Spark,[27] with the assistance of a Royal Australian Air Force (RAAF) Boomerang that was on station overhead to provide aerial observation.

[37] By dawn, Downs' company was taking sporadic fire from Japanese pill boxes, and they began patrolling forward of their perimeter to locate these positions.

In order to defend themselves the Australians called down heavy artillery fire from the battery of 25-pounders that was supporting them from its position on the Soraken peninsula.

[53] As rations and water dwindled, unsuccessful attempts were made on 10 June to rescue the men in the stranded barge with support from artillery and aircraft.

While Corsairs flew close support missions, Beaufort and Mitchell bombers dropped life rafts but the survivors were unable to reach them due to machine-gun fire.

[34] Other men swam over 5 kilometres (3.1 mi) through the shark-infested waters to Torokori Island,[50][54] while others were either rescued at sea or managed to link up with the Australians along the Ratsua front, who had been attempting to break through to them but found themselves checked 500 yards (460 m) from them,[57] by sneaking through the Japanese lines from the rear.

[59] The 23rd Brigade under Brigadier Arnold Potts took over control of the sector, and for a period of four weeks along the Ratsua front the 8th and 27th Infantry Battalions carried out patrolling operations before the Australians decided to withdraw to the Buoi Plantation in mid-July,[60] by which time the Japanese forces in the area, boosted by their victory at Porton, had begun to seize the initiative through the use of harassment tactics.

Both James and Davidson state that several aspects of the planning undertaken by 11th Brigade staff and the 31st/51st Infantry Battalion's commander contributed to the defeat,[63][64] particularly in relation to the failure of intelligence to adequately identify the risks posed by the nearby reefs, as well as the failure to adequately resource the operation, and an overestimation of the ability of neighbouring forces to breakthrough to the beachhead.

[65][66] James agrees that it was under resourced, stating that the size of the assault force was "too small to establish a beachhead and push inland as well", although ultimately argues that the campaign was necessary.

In support of this, James outlines that in the aftermath of the fighting, Blamey visited Kelly at his headquarters around Ratsua and upon interviewing him, stated to the II Corps commander, Savige, that he felt that Kelly had erred in conducting rehearsals of the barge landings during the planning stage within view of Japanese positions, potentially warning them of the operation.