Borneo campaign
On the 1st of May 1945, Australian soldiers paddled toward a small island off the north-east coast of Borneo in handmade folboats, slipping past Japanese-held oilfields before the main assault wave arrived. That opening move on Tarakan kicked off the Borneo campaign, the last major Allied operation in the South West Pacific Area during World War II. Its formal designation was Operation Oboe, an umbrella name for a series of amphibious assaults aimed at wresting British and Dutch Borneo back from Imperial Japan. The campaign would run from May through July 1945, involve more than 74,000 Allied troops, and end with a verdict that still divides historians: a series of skillfully executed operations that achieved, strategically speaking, very little.
Before the Pacific War broke out, Borneo was split between British control in the north and Dutch control in the south, the latter being part of the Netherlands East Indies. As of 1941, the island held an estimated population of 3 million people, most of them living in small villages scattered across dense jungle and coastlines lined with mangroves and swamps. Fewer than a dozen towns existed on the whole island, and roads were scarce; most travel moved by watercraft along the rivers.
Japanese forces moved fast when the Pacific War began. Troops landed at Sarawak on the 16th of December 1941, where a single British Indian battalion fought a delaying action over several weeks and managed to damage key oil installations before being pushed back. On the 11th of January 1942, Japanese troops landed on Tarakan, while parachute troops dropped on the Celebes the following day. The Dutch garrison there destroyed some infrastructure before being overwhelmed. Those acts of sabotage drew brutal reprisals. At Balikpapan alone, between 80 and 100 Europeans were executed.
The occupation that followed was harsh and systematic. On Tarakan, large numbers of people were conscripted as labourers, the local economy was wrecked, and food grew scarce. In October 1943, Dayak tribesmen and ethnic Chinese launched an open revolt known as the Jesselton revolt. The Japanese crushed it violently, executing hundreds, and the repercussions stretched further still as more people died from disease and starvation under the restrictive policies that followed. The garrison, small through most of the occupation, grew significantly from mid-1944 as Allied forces advanced across the Pacific and Japan began preparing Borneo for defence.
Planning for the Borneo operation began in late 1944 and early 1945 at General Douglas MacArthur's South West Pacific Area headquarters. The campaign sat within a broader scheme called Operation Montclair, which aimed at re-occupying the Netherlands East Indies, Sarawak, Brunei, and British North Borneo. Borneo was valued chiefly for oil and rubber, and Tarakan was specifically identified as a site for a forward airbase to support future operations.
The task of taking Borneo fell mainly to Australian ground forces. American troops were committed to the Philippines, so MacArthur assigned the Australian I Corps, under Lieutenant-General Leslie Morshead, to the job. The corps had not seen combat for over a year. MacArthur had previously declined to use it in the Philippines despite pressure from the Australian Government.
The original plan outlined six stages. Oboe 1 targeted Tarakan; Oboe 2 aimed at Balikpapan; Oboe 3 at Banjarmasin; Oboe 4 at Surabaya or Batavia, now known as Jakarta; Oboe 5 at the eastern Netherlands East Indies; and Oboe 6 at British North Borneo. In the end, only four locations saw actual landings: Tarakan, Labuan, North Borneo, and Balikpapan.
Not everyone in Australian leadership was convinced by the plan. General Thomas Blamey, commander of the Australian Military Forces, recommended against the Balikpapan landing, arguing it would serve no strategic purpose. The Australian Government eventually agreed to provide forces at MacArthur's urging, though Blamey did succeed in persuading Prime Minister John Curtin to withhold the 6th Division, blocking MacArthur's plans for follow-on landings in Java. Before any of the main landings took place, Allied reconnaissance operations codenamed Agas and Semut were already underway, arming and organising local populations to fight the Japanese from within the island's interior.
Brigadier David Whitehead commanded the 26th Brigade, the force assigned to take Tarakan, and his command was formidable on paper. Three infantry battalions were augmented by two pioneer battalions, commandos, engineers, American amphibious engineers, the 727th Amphibian Tractor Battalion, and a Dutch company drawn from soldiers from Ambon Island. Total strength came to just under 12,000 troops. A heavy aerial bombardment had been underway since the 12th of April, with RAAF and US aircraft flying from Morotai Island and the Philippines to hit shipping, airfields, and defensive positions.
The assault on the 1st of May met no resistance at the water's edge. Troops from the 2/23rd and 2/48th Infantry Battalions came ashore under naval barrage, swept past Lingkas and pushed north toward Tarakan town. The airfield fell on the 5th of May, but the fight was not clean. Mines and booby traps slowed every step forward. Japanese troops held tunnels and high ground across the island, and the final major objective, Hill 90, was not secured until the 20th of June. Small-scale clashes persisted even after that.
The airfield, the very reason for taking the island, turned out to be so badly damaged that it took eight weeks to repair. By the time it was operational, the war was nearly over. Australian official historian Gavin Long concluded that the invasion of Tarakan did not justify the cost. Australian casualties were 225 killed and 669 wounded. Japanese losses were far heavier: 1,540 killed and 252 captured. The destruction of Tarakan's infrastructure during the preparatory bombardment also inflicted at least 100 civilian casualties before a single soldier stepped ashore.
Oboe 6 opened on the 10th of June with simultaneous assaults against Labuan island and the coast of Brunei. Major General George Wootten's 9th Division led this phase, with 29,000 personnel assigned in total. A reconnaissance party including Sergeant Jack Wong Sue had earlier paddled into Kimanis Bay by folboat, deployed from a Catalina aircraft, to gather intelligence close to shore. The landings themselves met almost no resistance; Japanese forces had pulled back from the coast and the Australians walked ashore.
The 24th Brigade's experience on Labuan proved harder. After quickly taking the airfield and the town, the brigade ran into a well-defended Japanese stronghold. An initial assault by the 2/28th Battalion on the 16th of June suffered heavy casualties. Sustained bombardment was ordered, and when the battalion attacked again on the 21st of June with tank support, the position fell. The 24th Brigade counted 34 killed and 93 wounded on Labuan; 389 Japanese bodies were found and 11 prisoners taken.
The conventional fighting on the mainland was shadowed by a separate guerrilla campaign run by Special Operations Australia. Operation Agas covered British North Borneo and Operation Semut covered Sarawak. Over 100 Allied personnel, mostly Australian, were inserted into Sarawak by air from March 1945, while five separate Agas parties moved into North Borneo between March and July. The interior Dayak population joined enthusiastically, and SOA personnel led what amounted to small private armies. No. 200 Flight RAAF and Royal Australian Navy Snake-class junks inserted personnel and supplies. Operating from patrol bases near Balai, Ridan, and Marudi, and along rivers including the Pandaruan and Limbang, these forces are estimated to have killed over 1,800 Japanese across north Borneo. The heaviest conventional fighting on the mainland occurred on the 27th and the 28th of June at the Battle of Beaufort, where more than 100 Japanese defenders were killed.
Beyond combat, the 9th Division took on the largest civil affairs task Australian forces undertook during the entire war. Aid was given to civilians, and housing and infrastructure destroyed by pre-invasion bombardment were rebuilt.
The final amphibious assault of World War II took place at Balikpapan on the 1st of July 1945. The attack had been prepared over 20 days of aerial bombardment and 15 days of minesweeping to clear channels and anchorages for the fleet, all conducted within range of Japanese coastal guns. Three minesweepers were lost during that clearing effort. The invasion fleet sailed from Morotai Island on the 26th of June and arrived off Balikpapan on the 29th. Before the troops landed, the warships delivered over 45,000 rounds of preparatory fire.
Major General Edward Milford commanded the 33,000-strong force, with 21,000 from his Australian 7th Division. It was the first time the division's three brigades, the 18th, 21st, and 25th, had fought together as a complete formation. A deception plan drew Japanese attention toward Manggar while the real assault concentrated on the southern coast between Klandasan and Stalkoedo. Smoke from the bombardment made navigation difficult and the initial wave landed at the wrong location, but the beach was undefended and a beachhead was established quickly.
Balikpapan town and the port fell on the 3rd of July, though clearing operations ran into the 4th. The 21st Brigade pushed east along the coast toward airfields at Sepinggang and Manggar, crossing the Batakan Ketjil River before being stopped by strong Japanese resistance that required naval gunfire to break. When the brigade crossed the Manggar Besar River the following day, it faced even stronger opposition backed by coastal artillery and mortars. The airfields were not secured until the 9th of July. Australian engineers cleared more than 8,000 mines and booby traps and destroyed over 100 tunnels in the fighting around the town. The 25th Brigade pushed inland along a road the Australians named the Milford Highway, driving the Japanese rearguard back to a secondary position by the 9th of July before forcing a further withdrawal by the 21st and the 22nd of July. Mopping-up operations continued until the war ended in August. The Balikpapan operation cost 229 Australians killed and 634 wounded; 2,032 Japanese were counted killed and 63 captured.
When the shooting stopped, Australian personnel stayed in Borneo through late 1945 to restore civilian administration, oversee reconstruction, supervise Japanese surrenders, and liberate prisoners of war held in camps including Sandakan and Batu Lintang. Allegations arose that Australian forces near Beaufort encouraged local fighters to massacre surrendered Japanese soldiers in revenge for the Sandakan Death Marches, with claims of almost 6,000 Japanese killed in this way. Historian Ooi Keat Gin notes that no documentary evidence supports these claims.
Historian Eustace Keogh called the amphibious operations the outstanding feature of the campaign and the largest of their kind the Australians conducted during the war. Peter Dennis assessed them as of doubtful strategic value but skillfully conducted. The critic went further: historian Max Hastings argued that Japanese forces, already cut off from Japan, could simply have been contained by token Allied screening forces until their own nation's surrender compelled them to lay down arms.
Allied casualties across the whole campaign totalled about 2,100. Japanese casualties reached about 4,700. Pre-invasion bombardments had also done considerable damage to the very infrastructure the Allies sought to capture; the oil production facilities at Tarakan and Balikpapan suffered heavily, stripping the campaign of much of the strategic return it had promised. The campaign was widely criticised in Australia at the time and in the years that followed as a waste of soldiers' lives, particularly after the outcome at Tarakan. Whatever the verdict on the strategy, one concrete result the Allied landings did produce was the freeing of Allied prisoners of war who were being held in worsening conditions when the fighting began.
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Common questions
What was the Borneo campaign in World War II?
The Borneo campaign, also called the Second Battle of Borneo, was the last major Allied campaign in the South West Pacific Area during World War II. Conducted under the name Operation Oboe, it consisted of a series of amphibious assaults between the 1st of May and the 21st of July 1945, aimed at liberating British and Dutch Borneo from Japanese occupation.
Who commanded the Australian forces in the Borneo campaign?
Lieutenant-General Leslie Morshead commanded the Australian I Corps, the main Allied ground force in the campaign. The corps included the 7th Division under Major General Edward Milford and the 9th Division under Major General George Wootten.
What were the main battles of the Borneo campaign?
The campaign involved landings at four locations: Tarakan (the 1st of May 1945), Labuan and the Brunei coast (the 10th of June 1945), and Balikpapan (the 1st of July 1945). Balikpapan was the last major amphibious assault of World War II.
What were the casualties in the Borneo campaign?
Allied casualties across the entire campaign totalled about 2,100. Japanese casualties reached about 4,700. At Tarakan alone, 225 Australians were killed and 669 wounded, while 1,540 Japanese were killed and 252 captured.
Why was the Borneo campaign considered strategically questionable?
Historians including Max Hastings argued that Japanese forces in Borneo were already cut off from Japan and could have been contained until their nation's surrender forced them to lay down arms. Pre-invasion bombardments heavily damaged the oil facilities the campaign aimed to capture, making the strategic gains negligible.
What role did Dayak guerrillas play in the Borneo campaign?
Special Operations Australia organised Dayak tribesmen and other local fighters through Operation Agas in British North Borneo and Operation Semut in Sarawak. Over 100 Allied personnel were inserted into Sarawak from March 1945, and guerrilla forces are estimated to have killed over 1,800 Japanese across north Borneo.
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