The Battle of Porton Plantation (8–10 June 1945) took place near the village of Soraken on Bougainville Island, in the Solomon Islands archipelago during World War II. 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. The battle formed part of Australian efforts to liberate the northern part of Bougainville.
The fighting occurred after a company-sized Australian force from the 31st/51st Infantry Battalion made an amphibious landing north of the Porton Plantation jetties in an attempt to outflank the Japanese positions on the Ratsua front, which were holding up the advance of the 26th and the 31st/51st Infantry Battalions from the 11th Brigade. The Australians landed unopposed and established a small perimeter, but some of their landing craft ran aground and they were unable to bring their heavy weapons and support elements ashore. Troops from the Japanese 87th Naval Garrison Force quickly surrounded the beachhead and, as their supply situation grew desperate, the Australians were forced to withdraw. In the course of their evacuation by sea another landing craft ran aground. 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.
The battle was a victory for the Japanese and it proved instrumental in helping them to regain the initiative in the northern sector of Bougainville. 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. Since the end of the war, there has been considerable criticism of the planning undertaken by the Australians prior to the operation, and it has been argued that the operation failed due to poor intelligence and lack of resources and was ultimately unnecessary.
Background
Strategic situation
Japanese forces had landed on Bougainville in early 1942, capturing it from the small force of Australians garrisoning the island. They had subsequently developed several airbases on the island, using it to conduct operations in the northern Solomon Islands and to attack the Allied lines of communication between the United States, Australia and the Southwest Pacific Area. These bases also helped protect Rabaul, the major Japanese garrison and naval base in Papua New Guinea, and throughout 1943, Allied planners determined that Bougainville was vital for neutralising the Japanese base around Rabaul. 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. In March 1944, the Japanese launched a heavy counter-attack, which was turned back with many casualties. After this, the situation on Bougainville became largely static, as the Japanese focused primarily on subsistence, and the US forces chose to adopt a mainly defensive posture focused on maintaining the perimeter around Torokina.
On 22 November 1944, the Australian II Corps, consisting mainly of Militia troops under the command of Lieutenant General Stanley Savige, took over responsibility for Allied operations on Bougainville from the US XIV Corps. Throughout November and December Australian units began relieving the Americans who were then redeployed on subsequent operations in the Philippines. Although Japanese forces on Bougainville actually numbered around 40,000 men at the time, Allied intelligence failed to determine this accurately, estimating that there were only about 17,500 defenders. As a result of this error, Australian planning staff believed that they were opposed by a roughly equal-sized force and the Australian corps commander, Savige, under orders from General Thomas Blamey, commander-in-chief of the Australian Military Forces during the war, to "destroy... [Japanese]...resistance...without committing major forces" and limiting casualties, consequently decided that he would pursue a limited offensive campaign to clear the Japanese from Bougainville. 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. Supporting operations were also conducted along two other fronts. 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. The Australian troops were largely inexperienced, but were according to historian Karl James "fresh...[and] well equipped". For their part, according to James, the Japanese force on Bougainville had been "...reinforced from Rabaul with troops, weapons and equipment" and although much of 1944 had been spent foraging and establishing food supplies on the island, there was only "enough food reserves for four months".
The build up of Australian forces was hampered by a lack of resources, which were focused largely upon the US operations in the Philippines, and Australian operations in Borneo, which was considered the priority, and ultimately these considerations would impact upon Australian strategy upon the island due to the limited amount of amphibious support available. After initial moves by the Australians to take over the US perimeter at Torokina and garrison the Outer Islands in September and October, in November the Australians took over officially from the Americans. Later that month, troops from the 7th Brigade left the perimeter and took over from the small US forces holding outposts along the Numa Numa Trail in the centre of the island. From there, a couple of minor skirmishes followed culminating in the Battle of Pearl Ridge. In late December, the 11th Brigade, under the command of Brigadier John Stevenson, took over control of the northern sector of the island from the 7th Brigade, which was transferred to the southern sector to take part in the main offensive. Throughout January, as part of efforts to liberate the northern part of the island, the brigade advanced north along the coast from Kuraio Mission, clearing the main settlements while sending patrols inland in an effort to flush out the Japanese from the high features in an effort to draw them into fighting in the open. In mid-January the lead Australian battalion, the 31st/51st Infantry Battalion, under the command of Lieutenant Colonel Joseph Kelly, came up against a strong Japanese position at Tsimba Ridge and over the course of three weeks fought to gain control of the feature. The Australians lost 23 killed and 53 wounded while the Japanese had at least 66 men killed.
Preliminary moves
Following the fighting on Tsimba Ridge, the 31st/51st was relieved by the 26th Infantry Battalion, and the Australians continued to advance north towards Soraken. Over the course of several months, the 26th advanced on several axes: from Downs' Ridge they crossed the Nagam River, while on the coast another element advanced through Lalum to the Compton River. Between these two forces, another linked up with those that had crossed the Nagam, and proceeded north over the Compton towards Soraken Plantation. Elsewhere, barges were used to land forces on the Soraken Peninsula in several locations to dislocate the Japanese forces there and sever their lines of communication, while other landings took place on Saposa Island and Torokori Island. In April, the 26th was relieved by the 55th/53rd Infantry Battalion which advanced north to Ratsua, from where the Australians planned to move along the Bonis Peninsula. By late May, however, casualties amongst the 55th/53rd meant that they had to be withdrawn from the line, and the 26th Infantry Battalion was moved back up to replace them, along with the 31st/51st. At the start of June the Australians were stretched out across a 8-kilometre (5.0 mi) line between Ratsua to Ruri Bay.
On 4 June, the 31st/51st Infantry Battalion began patrolling operations around Buoi Plantation. Two companies, 'B' and 'D', were committed to these operations with 'B' Company focusing upon the north-eastern part of the plantation, while 'D' Company patrolled to their east. Clashes followed over the next three days; the Australians lost one killed, and the Japanese 10. 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, 5 kilometres (3.1 mi) to the north of Ratusa, 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. During the planning phase, concerns were raised by several officers about the size of the force allocated and the distance that the breakthrough force would be required to advance to link up with the force landing at the beachhead, but these were ultimately discounted. On the evening of 5 June, the Australian battalion commander outlined his plan and in the afternoon of the following day rehearsal landings were undertaken. Final preparations were made on the night of 6/7 June and continued throughout the next day.
Opposing forces
The Australian landing force consisted of 190 men embarked on six landing craft. The bulk of the force was made up of infantry from 'A' Company and a platoon from 'C' Company, 31st/51st Infantry Battalion under the command of Captain Clyde Downs. Artillery support was provided by the 11th and 12th Batteries of the 4th Field Regiment and the 2nd Mountain Battery. Other supporting units included engineers from the 16th Field Company and 42nd Assault Landing Craft Company, medical support from the 19th Field Ambulance and logistics support from the 223rd Supply Platoon. Although aerial reconnaissance indicated that there were strong Japanese fortifications in the area, initially no air support was allocated to the operation, with requests for preliminary air strikes being denied by II Corps as they were, according to James, not "considered to be suitable air targets". The Japanese force in the immediate vicinity initially consisted of about 100 men from the Imperial Japanese Navy's 87th Naval Garrison Force which had been formed from men drawn from the 211th Pioneer Unit interspersed with regular naval personnel. However, over the course of the battle the strength of the Japanese force grew to between 400 and 500 men. The Japanese force was commanded by the senior naval officer at Buka, Captain Eikichi Kato, whose 87th Naval Garrison Force had taken over responsibility for the defence of the Tarlena area when the Imperial Japanese Army's 38th Independent Mixed Brigade was transferred south to the Numa Numa area.
Battle
Initial landing and fighting around the beachhead
At 3:57 am on 8 June the first wave of Australian troops landed on the beach in three landing craft. 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. A series of forward positions were then established a further 50 yards (46 m) inland. Instead of pushing his rifle platoons further inland, however, Downs decided that he would wait for the second wave to arrive. This ultimately proved critical as it allowed the Japanese commander, Kato, time to respond to the landing. As the three landing craft of the first wave withdrew, another three landing craft came in with reinforcements, heavy weapons and other support elements, however, they ran aground on a coral reef and the men aboard were forced to wade ashore. Although one of these craft was later able to float free, two of the others remained stuck. A short time later they began to take fire from Japanese machine-guns, which stopped the Australians from unloading their equipment.
Lacking organic indirect fire support as all the mortars had been in the landing craft that were in the second wave, 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, with the assistance of a Royal Australian Air Force (RAAF) Boomerang that was on station overhead to provide aerial observation. By dawn, Downs' company was taking sporadic fire from Japanese pill boxes, and they began patrolling forward of their perimeter to locate these positions. These patrols were unable to progress very far before they were forced back by Japanese fire, which confirmed how bad the company's position was. They determined that they had landed about 270 yards (250 m) north of where they had been supposed to land, and inside what the official historian Gavin Long described as an "arc of enemy trenches and pill-boxes with a radius of about 400 yards" that effectively boxed them in.