The Battle of North Borneo took place during the Second World War between Allied and Japanese forces. Part of the wider Borneo campaign of the Pacific War, it was fought between 10 June and 15 August 1945 in North Borneo (later known as Sabah). The battle involved a series of amphibious landings by Australian forces on various points on the mainland around Brunei Bay and upon islands situated around the bay. Japanese opposition to the landings was sporadic initially, although as the campaign progressed a number of considerable clashes occurred and both sides suffered significant casualties, although major combat was largely restricted to Labuan and around Beaufort. On the mainland, while Allied conventional operations focused largely on the coastal areas around Brunei Bay, guerrilla forces consisting of Dayak tribesmen and small numbers of Allied personnel from the Services Reconnaissance Department fought an unconventional campaign in the interior. The Allies were successful in seizing control of the region. Nevertheless, many of the strategic gains that possession of North Borneo provided were ultimately negated by the sudden conclusion of the war in August 1945.
Background
Strategic situation and planning
Codenamed Operation Oboe Six, the battle was part of the second phase of the Allied operations to capture the island of Borneo. North Borneo had been occupied by troops from the Imperial Japanese Army since early 1942 following the Japanese invasion of Borneo; prior to this the area had been a British territorial possession. Following its occupation, the area's oil resources had been exploited for the Japanese war effort. The island's population had also been subjected to harsh occupation policies. This had led to a revolt at Jesselton in late 1943, which was suppressed by the Japanese with heavy civilian casualties.
The first stage of the Allied campaign in Borneo had begun in May 1945 when a brigade-sized force had been put ashore on Tarakan, on the north-eastern side of Borneo. The operation in North Borneo was planned by General Douglas MacArthur's South West Pacific Area command. Designed with three phases—preparatory bombardment, forced landings, and an advance—the objective of the Allied operation was to establish "an advanced fleet base" for the British Pacific Fleet in Brunei Bay, which offered the Allies a deep-water port, to enable subsequent naval operations. Further objectives included capturing the vast oil and rubber supplies available in the area and re-establishing British civil administration. It was also intended that Labuan would be secured to control the entrance to Brunei Bay, and would be developed as an airbase. In the planning phase of the operation, the Allied high commands differed in their opinions about the necessity of securing Brunei, with the British Chiefs of Staff Committee believing it would take too long to develop the area for it to be developed for it to be used in operations. They were also concerned that it would divert the British Pacific Fleet from the main theatre of operations off Japan and instead favoured establishing a fleet base in the Philippines. The United States Joint Chiefs of Staff, however, approved the operation believing that it could support future operations in south-east Asia.
In preparation for the landings, commencing in March, the Allied Services Reconnaissance Department (also known as Special Operations Australia) began Operation Agas in North Borneo, and Operation Semut in Sarawak; these were clandestine operations to gather information and organise local Dayak tribesmen to carry out guerrilla operations following the main landings. Ultimately, five Allied parties would be inserted into Borneo as part of Operation Agas, while four were deployed under Semut. Preliminary aerial bombardment of northern Borneo by Australian and US aircraft began on 3 May, before being concentrated on the main landing areas on 5 June. Meanwhile, minesweepers began to clear sea lines of communication for the large Allied naval task force that was assigned to support the operation. This force was designated as Task Force 78.1 and consisted of Australian and US warships, under the command of Rear Admiral Forrest B. Royal. Initially, the Allies planned to launch operations in North Borneo in late May, but shipping shortages delayed moving the assault troops to their staging base on Morotai Island and resulted in the operation being delayed until early June.
Opposing forces
A total of 29,000–30,000 men were committed by the Allies to secure North Borneo, with the majority of the ground forces being provided by the Australian 9th Division, under the command of Major General George Wootten. The 9th Division consisted of three brigades—the 20th, 24th and 26th Brigades—however, at the time of the North Borneo operations, the 26th was engaged at Tarakan having been detached from the division in May 1945, so only two brigades were allocated to operations in North Borneo. Part of the all-volunteer Second Australian Imperial Force, the 9th Division was a veteran formation, having previously served in North Africa, the Middle East and New Guinea. Prior to the Borneo campaign, the division had been resting and reorganising on the Atherton Tablelands in Queensland. The division had experienced a high turn over in personnel following its service in the Huon Peninsula campaign as soldiers were medically discharged or transferred to other units. In addition to the Australian ground troops, naval support was provided by the United States Navy and Royal Australian Navy and aerial support from the United States Army Air Force's Thirteenth Air Force, the United States Marine Corps, and elements of the Royal Australian Air Force's 1st Tactical Air Force. Two United States Army units, the 727th Amphibian Tractor Battalion who manned the LVTs and the 593rd Engineer Boat and Shore Regiment's Boat Battalion, were also attached to the Australians.
Meanwhile, Allied intelligence estimated that there were approximately 31,000 Japanese troops on Borneo, with about 8,800 of these in North Borneo. The Japanese Thirty-Seventh Army, led by Lieutenant-General Masao Baba, was tasked with defending the area, and was headquartered in Jesselton. The main Japanese units in the vicinity included elements of the 56th Independent Mixed Brigade, consisting of six battalions (the 366th to the 371st), along with another independent battalion. This brigade was commanded by Major General Taijiro Akashi. It had been raised in Japan during the second half of 1944 and arrived in Borneo late that year as the area's garrison troops were reorganised for defence against future Allied landings. By mid-1945, the brigade had been heavily depleted by its overland movement from the north-eastern part of Borneo prior to the Allied landings and was at around half strength; its troops were largely inexperienced, lightly equipped and were suffering from poor morale. Japanese air power in the region had been heavily depleted and, except in Java and Sumatra, was ineffective, although there were small numbers of aircraft at Keningau and Kuching.
Battle
Labuan
Two main landings were undertaken by the Australians in North Borneo on 10 June. After concentrating at Morotai Island in May, where complex landing rehearsals were undertaken, the assault force, consisting of 85 ships—mainly from the US Navy—departed in early June, preceded by minesweepers and survey vessels, as well as the naval attack group. The first landing was made when troops from two battalions of Brigadier Selwyn Porter's 24th Brigade—the 2/28th and 2/43rd Battalions—landed on Labuan Island with a squadron of Matilda tanks from the 2/9th Armoured Regiment. The 24th Brigade's third battalion, 2/32nd Battalion, was placed in divisional reserve for the initial landing. The attack was preceded by a heavy naval bombardment from cruisers, mortar and rocket ships, and attacks by eight Liberator heavy bomber squadrons which used anti-personnel bombs to target Japanese troops around the intended beachheads. With this support, the main Allied landings were largely unopposed as the Japanese defenders had withdrawn from the beaches on the peninsula and Muara Island had been abandoned completely. At Labuan, the Australian troops came ashore near Victoria and, supported by a heavy artillery and naval gunfire support, the two battalions drove towards the airfield. Light opposition was overcome and the town and airfield were secured late on the first day, after minor clashes with Japanese outposts and troops fighting amongst the aircraft dispersal bays. Meanwhile, the 2/11th Commando Squadron provided flank support to the west.
Despite the initial progress the fighting on Labuan intensified during this time as the Japanese defenders retreated inland to a heavily fortified position known as "the Pocket" and attempted to hold the Australians along the dense jungle ridges and thick swamps. The 2/12th Commando Squadron was brought ashore from divisional reserve on 12 June and was given the task of clearing the outlying areas of resistance that had been bypassed during the initial advance on the island, By 14 June, the Australians had secured the island, apart from those Japanese contained within the Pocket. Despite considerable artillery and armoured support, a company-level attack by the 2/28th Battalion was turned back on 14 June, and as a result further preparatory fires were called upon to soften up the Japanese defences.
At this stage of the war, Australian commanders were under strict orders to limit their casualties, and "avoid unnecessary risks", utilising fire support where possible to reduce Japanese defences prior to attacking. Commencing on 17 June, an intense three day naval and aerial bombardment was laid down in an effort to reduce the Japanese defences. Meanwhile, 100 Japanese attacked the Australian brigade's maintenance area and the airfield before the Australians launch a renewed attack on 21 June. At this time, two companies of infantry from the 2/28th Battalion assaulted the Japanese position. Supported by indirect fire support from sea and air, and direct fire support from tanks and flamethrowers, the Australians overwhelmed the Japanese defenders and cleared the remaining resistance from Labuan. After the battle 180 Japanese dead were counted, bringing the total killed during the fighting on Labuan to 389. Against this the Australians suffered 34 killed and 93 wounded.
Brunei and Muara Island
The second Allied landing that took place on 10 June, consisted of two battalions of Brigadier Victor Windeyer's 20th Brigade—2/15th and 2/17th Battalions—landing at Muara Island and on the mainland peninsula north of Brooketon, supported by a second squadron of Matildas from the 2/9th Armoured Regiment. The 20th Brigade's third battalion, the 2/13th, was held back in brigade reserve. Meanwhile, in the interior, Dayak tribesmen supported by Allied operatives commenced their guerrilla campaign on 9 June. Lightly armed, and with only limited training, these guerrillas sought to harass the withdrawing Japanese, while avoiding decisive engagement. In this role, they met with some success, but were in some cases forced to withdraw in the face of heavy opposition. The troops that had landed near Brooketon on the mainland advanced on Brunei, which was captured on 13 June by the 2/17th Battalion after several minor section and platoon level actions over several days. The 2/15th, which had earlier secured Muara Island, secured Limbang on 18 June, advancing by landing craft up the river in the south-west of Brunei Bay. The two 20th Brigade battalions were now joined by the 2/13th Battalion, which had conducted an unopposed landing at Lutong on 20 June, supported by Spitfire and Kittyhawk fighters operating from Labuan, before continuing their advance down the south-western coast and then overland, passing through Miri and Seria on their way towards Kuching.