The Battle of Balikpapan was the concluding stage of Operation Oboe, the campaign to liberate Japanese-held British and Dutch Borneo. The landings took place on 1 July 1945. The Australian 7th Division, composed of the 18th, 21st and 25th Infantry Brigades, with a small number of Netherlands East Indies KNIL troops, made an amphibious landing, codenamed Operation Oboe Two, a few miles north of Balikpapan. The Allied invasion fleet consisted of around 100 ships. The landing had been preceded by heavy bombing and shelling by Australian and US air and naval forces. The Allied force totalled 33,000 personnel and was commanded by Major General Edward Milford, while the Japanese force, commanded by Rear Admiral Michiaki Kamada, numbered between 8,400 and 10,000, of which between 3,100 and 3,900 were combatants. After the initial landing, the Allies secured the town and its port, and then advanced along the coast and into the hinterland, capturing the two Japanese airfields. Major combat operations concluded around 21 July, but were followed by mopping-up operations, which lasted until the end of the war in mid-August. Australian troops remained in the area until early 1946.
Background
Geography
Situated 2,241 kilometres (1,392 mi) northwest of Darwin, on the east coast of Borneo, Balikpapan's importance lay in its oil production facilities and port facilities. Prior to the war, the area produced 1.8 million tons of oil products a year. The town's port, sitting inside Balikpapan Bay, consisted of seven piers and a large number of warehouses. The port area was serviced by well-developed roads. At its mouth, the bay was 1 mile (1.6 km) wide, and was suitable for medium-sized ships. To the south of the port, an oil refinery with 40 storage tanks and a cracking plant lay along a steep ridge, separating the port from the European suburb of Klandasan, which looked out on the open sea from the cape that sat at the eastern part of the bay. Two roads fanned out from Balikpapan town, one running north-east to Samarinda – dubbed the "Milford Highway" by the Australians – while the other – the "Vasey Highway" – stretched south along the coast towards Sambodja. The oil refinery in Balikpapan was supplied with oil from fields around Sambodja and Sangasanga to the north-east.
To the east of the cape, the narrow coastal strip was serviced by road that extended east from Klandasan to Stalkoedo, Sepinggang, Batakan Besar, Manggar, and Sambodja crossing many rivers and streams. This road sat on a thick sandy strip of ground, just inland from the beach. The ground around the coast was largely flat, although there were some low hills which rose steeply further inland up to heights of 700 feet (210 m); while the area around the town and coast was largely open, the interior was heavily covered with thick rainforest. The dense vegetation limited cross country movement, although the rivers and streams were partially navigable. Two airfields had been established to the east of Balikpapan around Sepinggang and Manggar. Manggar was the larger of the two, consisting of two runways that had been graded out of coral. At the time of the Allied landings, the airfield had been badly damaged by aerial bombardment, while the second, smaller airfield, at Sepinggang had also been rendered unserviceable.
Balikpapan is located one degree south of the equator and has a tropical rainforest climate. The maximum temperature for most days in south-east Borneo in 1945 was about 72–86 °F (22–30 °C), and relative humidity was consistently high ranging from 74 to 93 percent. Monthly rainfall was fairly constant, averaging 6.9 inches (18 cm) in July. Allied intelligence estimates assessed that the July to September period represented that best period for military operations. In terms of cloud cover, July was generally clear and visibility was assessed as generally good. Wind speeds averaged 7 miles per hour (11 km/h) with south-south-westerly winds being the most prevalent during the May to November period.
Strategic situation
Prior to World War II, Balikpapan was under Dutch control, and formed part of the Netherlands East Indies. The Japanese occupied British Borneo and the Netherlands East Indies in late 1941 and early 1942. Balikpapan itself was seized on 25 January 1942. British and Dutch forces attempted to resist, but were quickly overwhelmed, but not before destroying or damaging the oil facilities and other important infrastructure. The destruction of these facilities led to harsh reprisals against civilians, particularly at Balikpapan, which was occupied in late January 1942, after which the entire European population – around 80 to 100 people – was executed. The facilities were subsequently repaired and by 1943–1944, Borneo had become one of Japan's main sources of fuel, crude and heavy oil; in 1943, Balikpapan provided 3,900,000 barrels (620,000 m3) of fuel oil to the Japanese war effort.
Throughout 1943 and 1944 the Allies attempted to reduce Japanese oil production at Balikpapan with air power. The first strategic bombing raids began in October 1943, undertaken by US Liberator bombers, flying 17 hours from bases around Darwin. Further raids took place in December 1943 and January 1944. In the early months of 1944, Royal Australian Air Force Catalina flying boats carried out a series of highly successful mining operations, which reduced the output of Balikpapan's facilities by an estimated 40 percent. In late September and early October 1944, the US Thirteenth and Fifth Air Forces began long range bombing raids from Noemfoor. The first two raids suffered heavy losses due to the lack of escort fighters and inflicted minimal damage; however, after a brief pause and a change of tactics by the US airmen, the final three raids resulted in heavy damage to the refineries and the destruction of most of the Japanese aircraft defending Balikpapan. This, coupled with Allied operations along Japanese sea lanes of communication, effectively cut off Japan from Balikpapan's oil supply line. The Japanese decided not to repair the damaged facilities, and those that remained were used for local supply only; indeed after October 1944, no more Japanese oil tankers were sent to Balikpapan; nevertheless, this simply diverted Japanese efforts to oil fields in Sumatra instead.
The Japanese advance in the Pacific was halted in early 1943, by Australian troops in New Guinea and US troops in Guadalcanal, after which the Allies went on the offensive, advancing through New Guinea and the Solomon Islands towards the Philippines. Throughout 1944, the Allies began planning to retake Borneo. The General Headquarters of General Douglas MacArthur's South West Pacific Area was responsible for planning the operation, but due to the commitment of US forces to the recapture of the Philippines, the task of recapturing Borneo was allocated primarily to Australian ground forces. Allied operations in Borneo consisted of landings at Tarakan, Labuan, and Balikpapan. Originally, MacArthur had intended to use Borneo as a stepping-stone to re-taking Java, but this operation was later cancelled and responsibility for the Netherlands East Indies transferred to the British-led South East Asia Command. In the planning phase the commander of the Australian Military Forces, General Thomas Blamey recommended against the landing at Balikpapan, believing that it would serve no strategic purpose. After much consideration, the Australian Government agreed to provide forces for this operation. The US Joint Chiefs of Staff also had concerns about the strategic necessity of the operation, but according to historian Garth Pratten, MacArthur manipulated both the Australian Government and the Joint Chiefs into approving the capture of Balikpapan. The stated purpose of the operation was, according to historian Chris Coulthard-Clark, "secure the port and oilfields in the area, and to establish a base from which to launch" future operations. Additionally, Netherlands East Indies governmental control would be re-established.
Opposing forces
Japanese preparations to defend against Allied landings in Borneo commenced in 1944, with the garrison forces being reorganised and an operational command being set up under the Thirty-Seventh Army. In early 1945, the Thirty-Seventh Army began reorientating its troops towards Borneo's west coast. The number of Japanese defending the area around Balikpapan in 1945 was around 8,400 – 10,000. Of these, between 3,100 and 3,900 were combatants. About 1,500 infantry and field artillery soldiers were in the Balikpapan–Manggar area, along with 1,500 anti-aircraft gunners. Base troops made up the rest of the number, along with between 1,100 and 4,500 armed Japanese, Formosan and Indonesian civilian labourers. Another 1,500 troops were 60 miles (97 km) away at Samarinda. The main Japanese units were Rear Admiral Michiaki Kamada's 22nd Naval Base Force and elements of the 71st Independent Mixed Brigade. The 22nd Naval Base Force's I Battalion was located around Klandasan and the Sumber River while the II Battalion was positioned around Batuchampar. Two other companies were around Penadjam. The Imperial Japanese Army's 454th Battalion had also been deployed to the Manggar area, having been transferred from Tarakan in March 1945. The Japanese holding Balikpapan town consisted of the 2nd Garrison Force – armed labourers, base troops, artillerymen along with a small number of marines – and elements of the 454th Independent Infantry Battalion. These troops possessed varying levels of training and their morale had been affected by weeks of preliminary bombardment. They were well equipped with heavy calibre weapons, but lacked lighter weapons. As a result, they were largely static in posture.
Due to the Allied interdiction of sea lanes of communication throughout the Pacific, Japanese troops on Borneo had found themselves increasingly isolated and by the end of 1944 supply shipments essentially ended. Food and supplies dwindled and units were forced to commence subsistence operations as the majority of troops began to suffer from malnutrition. Sanitation was also poor and due to limited medical supplies many Japanese troops became non-battle casualties. Nevertheless, the area was well supported with artillery, consisting of 18 Japanese coastal guns, concentrated around the ridges overlooking Balikpapan, along with 26 heavy guns and 78 medium and light anti-aircraft guns. These were orientated to defend the airfield, port and Balikpapan town itself. The defences in the area included a 12–14-foot (3.7–4.3 m) wide anti-tank ditch along the coast between Stalkoedo and Sepinggang, augmented by another around Klandasan. The beaches were dotted with Dutch-built concrete pillboxes while the Japanese had dug a complex trench system on the ridges overlooking the town. The seaward approach to Klandasan was defended by an underwater obstacle consisting of poles and barbed wire, which ran between Klandasan and Manggar. This was augmented by a large number of naval mines around the coast.
The operation was designated "Operation Oboe Two" by the Allies, who assigned 33,000 personnel. The main ground forces, amounting to 21,000 personnel, were drawn from Major General Edward Milford's 7th Division, a veteran Second Australian Imperial Force formation consisting of three infantry brigades – the 18th, 21st and 25th – along with supporting artillery, armour, engineer and logistics support units. The 7th Division had seen action earlier in the war in the Middle East and in New Guinea, but had been resting on the Atherton Tablelands in Queensland when they were assigned to the operation. The division's formation and unit-level command teams were all very experienced, but due to the high turn over of personnel that had occurred in the Australian Army in 1943–1944, many of its more junior personnel had not been in action before. Tank support was provided by the 1st Armoured Regiment, equipped with Matilda tanks. Naval support was drawn from the US 7th Fleet under Admiral Thomas Kinkaid, while air support came from the Australian First Tactical Air Force, and the US Thirteenth Air Force. Three US Navy escort carriers were also assigned to provide fighter support as the airstrip at Tarakan had not been made operational in time, and weather conditions hampered the provision of fighter support from the Philippines. A small number of Dutch KNIL troops, were also assigned to the operation, amounting to a company from the 1st Infantry Battalion (KNIL).