Borneo campaign
The Borneo campaign or Second Battle of Borneo was the last major Allied campaign in the South West Pacific Area during World War II to liberate Japanese-held British Borneo and Dutch Borneo. Designated collectively as Operation Oboe, a series of amphibious assaults between 1 May and 21 July 1945 were conducted by the Australian I Corps, under Lieutenant-General Leslie Morshead, against Imperial Japanese forces who had been occupying the island since late 1941 – early 1942. The main Japanese formation on the island was the Thirty-Seventh Army under Lieutenant-General Masao Baba, while the naval garrison was commanded by Vice-Admiral Michiaki Kamada. The Australian ground forces were supported by US and other Allied air and naval forces, with the US providing the bulk of the shipping and logistic support necessary to conduct the operation. The campaign was initially planned to involve six stages, but eventually landings were undertaken at four locations: Tarakan, Labuan, North Borneo and Balikpapan. Guerrilla operations were also carried out by Dayak tribesmen and small numbers of Allied personnel in the interior of the island. While major combat operations were concluded by mid-July, localised fighting continued throughout Borneo until the end of the war in August. Initially intended to secure vital airfields and port facilities to support future operations, preparatory bombardment resulted in heavy damage to the island's infrastructure, including its oil production facilities. As a result, the strategic benefits the Allies gained from the campaign were negligible.
Background
Prior to World War II, Borneo was divided between British Borneo, in the north of the island and Dutch Borneo in the south; the latter formed part of the Netherlands East Indies. As of 1941, the island's population was estimated to be 3 million. The great majority lived in small villages, with Borneo having less than a dozen towns. Borneo has a tropical climate and was mainly covered by dense jungle at the time of World War II. Most of the coastline was lined with mangroves or swamps.Borneo was strategically important during World War II. The European colonisers had developed oil fields and their holdings exported other raw materials. The island's location was also significant, as it sat across the main sea routes between north Asia, Malaya and the NEI. Despite this, Borneo was under-developed, and had few roads and only a single railroad. Most travel was by watercraft or narrow paths. The British and Dutch also stationed only small military forces in Borneo to protect their holdings.
Borneo was rapidly conquered by the Japanese in the opening weeks of the Pacific War. The purpose of this operation was to capture the oilfields and guard the flanks of advances into Malaya and the NEI. Japanese troops landed at Sarawak on 16 December 1941, where a single battalion of British Indian troops fought a delaying action over several weeks, damaging vital oil installations. Meanwhile, on 11 January 1942, Japanese troops landed on the island of Tarakan, while parachute troops carried out a drop on the Celebes the following day; the small Dutch garrison managed to destroy some of the infrastructure before eventually being overwhelmed. The destruction of these facilities led to harsh reprisals against civilians, particularly at Balikpapan where between 80 and 100 Europeans were executed.
In the aftermath, the Imperial Japanese Army administered the occupied British North Borneo and the Imperial Japanese Navy was responsible for Dutch Borneo. The garrison forces on the island were very small until mid-1944. During the occupation, the local population was subjected to harsh treatment. For example, on Tarakan large numbers of people were conscripted as labourers, the economy was disrupted, and food became increasingly scarce. In October 1943, an open revolt by local Dayak tribesmen and ethnic Chinese initiated the Jesselton revolt which was violently suppressed with hundreds being executed. In the aftermath, many more died from diseases and starvation as Japanese policies became even more restrictive on the local population. Japanese forces conducted a number of other massacres during their occupation of Borneo.
Planning
The plans for the Allied attacks were known collectively as Operation Oboe. The invasion of Borneo was the second stage of Operation Montclair, which was aimed at destroying Imperial Japanese forces in, and re-occupying the NEI, Raj of Sarawak, Brunei, the colonies of Labuan and British North Borneo, and the southern Philippines. Borneo in particular was considered at the time a strategic location for its natural resource; oil and rubber. Tarakan was also seen to offer a forward airbase to support future operations in the region, while Brunei Bay was intended to be used as naval base. Planning for the operation began in late 1944 and early 1945 through the General Headquarters of General Douglas MacArthur's South West Pacific Area. As a result of the commitment of US forces to the recapture of the Philippines, the task of recapturing Borneo was allocated primarily to Australian ground forces. By this time the Australian I Corps, the Australian Army's main striking force, had not engaged in combat for over a year. The corps had been assigned to MacArthur, but he had chosen to not use it in the Philippines despite the Australian Government pressing for this.The initial Allied plan comprised six stages: Operation Oboe 1 was to be an attack on Tarakan; Oboe 2 against Balikpapan; Oboe 3 against Banjarmasin; Oboe 4 against Surabaya or the capital of the NEI, Batavia ; Oboe 5 against the eastern NEI; and Oboe 6 against British North Borneo. In the end only the operations against Tarakan, Balikpapan and British North Borneo – at Labuan and Brunei Bay – took place. These operations ultimately constituted the last campaigns of Australian forces in the war against Japan. 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 at MacArthur's urging. Blamey was able to frustrate MacArthur's plans for Australian troops to make follow-on landings in Java by convincing Prime Minister John Curtin to withhold the 6th Division. Prior to the main landings in British North Borneo the Allies undertook a series of reconnaissance operations, codenamed Agas and Semut ; these operations also worked to arm, train and organise the local population to undertake guerrilla warfare against the Japanese to support conventional operations.
The Japanese military began to prepare for the defence of Borneo from mid-1944, as Allied forces rapidly advanced towards the island. IJA reinforcements were allocated to Borneo, but did not arrive until between September and November that year. In late 1944 the Japanese command judged that Australian forces were likely to attack the Brunei area and then capture the west coast of Borneo as part of a campaign aimed at liberating Singapore. Accordingly, most of the IJA units in north-eastern Borneo were ordered to move overland to the west coast; this required them to undertake gruelling marches over rugged terrain. Two other battalions were transferred from north-eastern Borneo by sea to south Borneo between February and March 1945. After United States forces liberated key areas of the Philippines, which cut the rest of South-East Asia off from Japan, on 27 January 1945 the IJA's General Staff ordered the forces in this area to defend the territory they held and not expect reinforcements.
Opposing forces
The main Allied ground forces assigned to the campaign came from the Australian I Corps, under Lieutenant-General Leslie Morshead. The main elements of this force consisted of two infantry divisions: the 7th and 9th. For the operation, the Australian corps was assigned as a task force directly under MacArthur's command rather than as part of the Eighth Army, which was controlling operations in the Philippines. Allied naval and air forces, centred on the U.S. 7th Fleet under Admiral Thomas Kinkaid, the Australian First Tactical Air Force, and the U.S. Thirteenth Air Force also played important roles in the campaign. A small number of Dutch personnel also took part in the operations. Over 74,000 Allied troops were assigned to the initial landings of the campaign. The bulk of the logistic support was provided by the US, particularly provision of the shipping that was required to transport the vast amounts of troops, stores and equipment required for the operation.Allied forces were resisted by IJN and IJA forces in southern and eastern Borneo, under Vice-Admiral Michiaki Kamada, and in the north-west by the Thirty-Seventh Army, led by Lieutenant-General Masao Baba, which was headquartered in Jesselton. The main elements of the Thirty-Seventh Army were the 56th Independent Mixed Brigade, 71st Independent Mixed Brigade and 25th Independent Mixed Regiment; these units had been raised in Japan during the second half of 1944 and arrived in Borneo late that year. The IJN's 2nd Naval Guard Force was also stationed in Borneo. Allied intelligence assessed that there were about 32,000 Japanese troops in Borneo, with 15,000 of these being combat troops. Most of the units which had been ordered from north-eastern Borneo to the west coast were still in transit when the Australian landings began and had been greatly weakened by the difficult conditions experienced during their cross-island march. The transfers left only single battalions and Balikpapan. Japanese air power in the region, except in Java and Sumatra, was ineffective.
Battles
Tarakan
The campaign opened with Oboe 1, which consisted of a landing on the small island of Tarakan, off the north-east coast on 1 May 1945. This operation was undertaken to capture the island's airstrip so that it could be used to support the subsequent landings on the mainland of Borneo. Using Australian-built MK III folboats, small parties of reconnaissance troops paddled into the Tarakan region to obtain useful information and observe the Djoeta oilfields prior to an invasion.The landing on Tarakan was assigned to the heavily reinforced 26th Brigade, under the command of Brigadier David Whitehead. This brigade's three infantry battalions were augmented with two battalions of pioneers as well as commandos and engineers. American amphibious engineers, an American amphibian tractor battalion, and a Dutch infantry company and civil affairs unit were also placed under Whitehead's command. Overall, the 26th Brigade had a strength of just under 12,000 troops. The Australian assault was preceded by a heavy aerial bombardment commencing 12 April, and undertaken by RAAF and US aircraft operating from Morotai Island and the Philippines; these aircraft interdicted Japanese shipping, attacked airfields, reduced obstacles around the landing beaches and suppressed artillery and defensive positions; in addition, a preliminary landing was undertaken on Sadau Island by a group of commandos and an artillery battery. Naval assets assigned to provide fire support during the operation include three cruisers, seven destroyers and several landing craft fitted with rockets and mortars. Three days prior to the assault, a force of minesweepers worked to clear the area of naval mines.
During the main landing, the battery on Sadau Island provided fire support to the Australian engineers who were landed at Lingkas to clear obstacles on the landing beaches. Assault troops from the 2/23rd and 2/48th Infantry Battalions came ashore under the cover of a strong naval barrage. Initially, they encountered no opposition before they began to advance north towards Tarakan town. Opposition around Lingkas Hill was overcome and by the end of the first day a strong beachhead had been established. The brigade reserve, the 2/24th Infantry Battalion, was landed the next day as the advance towards the airfield continued. Japanese resistance grew, and the advance was hindered by large numbers of mines and booby traps, which had to be cleared by engineers and pioneers; however, finally, on 5 May the airfield was captured by the Australians. Meanwhile, operations continued into June as isolated pockets of Japanese resisted the Australians in tunnels and on high features across the island. The final major objective, Hill 90, was secured on 20 June, but small scale clashes continued after this. Ultimately, the airfield was so heavily damaged that it took eight weeks to repair, by which time the war was essentially over. As a result, most historians, including the Australian official historian Gavin Long, believe that the invasion of Tarakan did not justify the casualties suffered by the Allied forces; these included 225 Australians killed and 669 wounded. Japanese casualties were even heavier, with 1,540 being killed and 252 captured.