The Borneo campaign of 1945 was one of the most complex operations involving Australian land, air and sea forces in the war. It was also the last Australian campaign to be planned and undertaken.
Borneo had been captured by the Japanese in early 1942. Most of the island was part of the Netherlands East Indies (modern Indonesia) but the north and north-west was British territory. During 1942 and 1943, many prisoners of war, including Australians, were sent to various locations on the island. In 1944, Australian special forces troops of the Services Reconnaissance Department – commonly known as 'Z' Force – were sent to the island to encourage Dyak villagers to engage the Japanese in guerrilla warfare. This was highly successful, with about 2000 Japanese killed.
The decision by the Allies to invade Borneo in 1945 was for the most part political. It had only marginal strategic value. General Douglas MacArthur, Commander-in-Chief of Allied forces in the South-West Pacific Area, planned the operation partly to alleviate concerns of the Australian government that its forces were being relegated to operational backwaters, as New Guinea had become. MacArthur had largely left Australian forces out of the most significant operation of this stage of the war – the liberation of the Philippines – with only some warships and a few air force units taking part. The invasion of Borneo was intended to make Australian forces more visible again in pressing home the war against Japan.
General MacArthur selected Borneo partly on the basis that bases on the island could be used to support an invasion of Java. The recapture of Java from the Japanese would formally restore control of the Netherlands East Indies to the Dutch. The Allies would also be able to capture the many oilfields in Borneo; however, this would have little effect on the war because American air and naval blockades of Japan had virtually cut off Borneo from Japan. No oil was reaching Japan from Borneo.
Senior Australian officers had misgivings about the operation but they ensured it was well planned. The high levels of training in the Australian forces meant the campaign would be skilfully conducted. The Army committed two veteran infantry divisions, the 7th and 9th Divisions, to the operation. Each had seen significant action in the Middle East and New Guinea. The Royal Australian Air Force's 1st Tactical Air Force was committed to supporting the operation, while the Royal Australian Navy committed warships and other units.
Three distinct operations were conducted. The first was on the island of Tarakan off north-east Borneo. It was to be captured and airfields established there. The operation was code-named OBOE 1. The 26th Infantry Brigade (part of the 9th Division) was allocated the task of taking the island. Its troops practised amphibious operations ahead of the actual landing from American landing ships and landing craft on 1 May 1945. Engineers went in first and cleared gaps through the beach defences with explosives before the main assault. Naval and air bombardments also destroyed or damaged many enemy positions. Over the next seven weeks, there was fierce fighting as the Australians pushed inland to take the whole island. More than 200 Australians were killed before the last Japanese positions fell on 20 June 1945. The dead included one of the most famous Australian soldiers of the war, Lieutenant Tom 'Diver' Derrick VC DCM, 2/48th Battalion, and also the sole recipient of the Victoria Cross for actions on Tarakan Island, Corporal John Mackey, 2/3rd Pioneer Battalion.
One of the primary objectives of landing on Tarakan Island was the construction of airfields to cover subsequent operations. However, airfield construction proved a much more difficult task than had been anticipated. 1 and 8 Airfield Construction Squadrons RAAF landed to repair and build airfields but found that the existing airfields were badly damaged and that excessively boggy ground in the area selected for new airfields impeded construction. Although opened to fighter aircraft in late June 1945, the airfields on Tarakan Island were not used to the extent that had been envisaged.
The second operation, code-named OBOE 6, was a landing on Labuan Island in Brunei Bay, north-west Borneo. The rest of the 9th Division landed with orders to secure the Brunei Bay area so it could be used as an advanced naval base. The secondary objective was to capture oilfields and rubber plantations and production plants. The landing had to be delayed by a few days because of shipping difficulties but on 10 June 1945 Australian troops stormed ashore. Smaller landings were made on nearby Muara Island and the Brunei Peninsula. Naval bombardments and air attacks helped clear the way for the troops as they advanced on each front. On Labuan Island, a force of several hundred Japanese made a determined stand in a swampy, jungle-clad area known as 'the pocket' – they were blasted out by naval and air attacks and infantry sent in to finish the job. Fighting continued on this front until the war's end, by which time more than 100 Australians had been killed.
The final operation, code-named OBOE 2, was at Balikpapan, south-east Borneo. It was the largest operation with more 33,000 army, air force and navy personnel landed from 1 July 1945 in the largest ever amphibious assault by Australian forces. As with the other operations, Australian troops were well supported with naval and air attacks which the Japanese could not match. The Australians also employed tanks to assist in attacking Japanese pill-boxes. This extra firepower cut down the numbers of casualties suffered by the Australians. Engineers were also employed to clear enemy minefields and destroy booby traps. Although the Japanese were able to mount some raids on Australian positions, there was never any doubt the Australian operation would succeed.
By the war's end on 15 August 1945, all major objectives had been achieved. But there was a sad footnote to the campaign with the loss of many prisoners of war who had been held at Sandakan in north Borneo. During 1942 and 1943, more than 2000 Australian and British prisoners of war had been sent there from Singapore and Java. They suffered dreadfully and by the start of 1945 many had died of starvation, overwork and disease. The Japanese ordered more than 1000 supposedly 'fit' men to march into the mountains to a more isolated base at Ranau. Nearly 300 men too sick to attempt the march either died or were killed at Sandakan. Of those who undertook the march, only six men – all Australians – survived. They had escaped and were rescued by Allied forces.