'Q' (i) was the Japanese seizure, from the British and Dutch, of the northern and western parts of Borneo, which is the world’s third largest island and the largest island of the East Indies archipelago (16 December 1941/1 April 1942).

In 1941, Borneo was divided between the Dutch East Indies and four British territories in the form of the protectorates of North Borneo, Sarawak and Brunei, and the crown colony of Labuan island.

The so-called 'White Rajahs' of the Brooke family had ruled Sarawak for almost a century, first as rajahs under the Sultanate of Brunei (entirely enclosed within the borders of Sarawak), and from 1888 as a protectorate of the British empire. The north-east of the island comprised North Borneo, since 1882 another British protectorate under the British North Borneo Company. Offshore lay the small British crown colony of Labuan island. The rest of the island, known collectively as Kalimantan, was under Dutch control.

In 'Q' (i), the Japanese were concerned primarily with the capture of the Raj of Sarawak, Brunei, North Borneo, and the western part of Kalimantan that was part of the Dutch East Indies. The Japanese main unit for this mission was Major General Kiyohide Kawaguchi’s 35^th Brigade.

Borneo was the largest Dutch land holding in the East Indies, even though the northern one-third of the island was under British control. Borneo is some 600 miles (965 km) on its east/west axis and t and is more than 500 miles (805 km) on its north/south axis, with an area of 284,000 sq miles (735555 km²) subdivided into Dutch Borneo (210,600 sq miles/545450 km²), North Borneo (29,500 sq miles/76405 km²), and the British protectorates of Sarawak and Brunei (50,000 and 2,226 sq miles/129500 and 57655 km² respectively). Borneo lies to the south-west of the Philippines island group, Celebes is to the east separated by the Straat Makassar, Java is to the south, and Sumatra and the Malay peninsula are to the west. The South China Sea reaches the north-western coast, the Sulu and Celebes Seas its north-eastern coasts, and the Java Sea its southern coast, and the equator passes through the island’s centre.

Borneo’s central interior from the eastern to the western coasts and the northern coast are extremely mountainous. Much of the interior was unexplored and the heights of the mountains were not accurately known. The highest peak is Mt Kinabalu on the north-eastern end of North Borneo, and at a height of 13,455 ft (4101 m) is also the highest in the East Indies. Most of the granite mountain chain running south-west/north-east through Sarawak and North Borneo ranges from 2,000 ft (610 m) to more than 7,000 ft (2134 m), as do the mountains in the interior. The mountains, covered by both dense rain forests and large scrub brush areas, are rugged with ridges and gorges cut by rivers and streams flowing toward the coasts. The largest river is the Barito flowing through the south-central portion of the island, and the capital Dutch Borneo was Bandjermasin, located near the river’s mouth. Other large river systems include the Mahakam on the east-central coast providing a fertile delta, the Kapoeas on the west-central coast, and the Mujong in western Sarawak. The larger rivers are navigable, but sandbars often block their mouths to large craft and rapids are found farther inland. Most of the south and lower western coasts are covered well inland by wide mangrove swamps. The rest of the lowlands are overgrown by thick forests. The coasts are rocky and often dangerous to small craft.

Villages are scattered along the coast, and the interior is dotted with remote villages even though the terrain is rugged. Most of these villages are located on rivers on which they rely for transport and communications. Rice farmers were forced to find suitable terrain well into the interior. Except in the few areas with fertile volcanic soil there is little good farming land. Spices, vegetables, fruits, rice, cotton, sugar cane, coconuts, coffee and tobacco were cultivated. Petroleum, tin, bauxite, manganese, nickel, copper, sulphur, coal, diamonds, platinum, gold and silver were mined. The main diamond mines were at Landak and Pontianak; the coal was in the Pengaron, Brunei, Kitei and Bandjermasin areas; and large oil-producing areas were on the Mahakam river delta and around Samarinda on the east-central coast and Tarakan island off the upper east coast. The oil was shipped from the new port at Balikpapan south of Samarinda. This was then one of the world’s richest oil production centres.

Borneo abounds with wildlife including monkeys, orangutans, tigers, tapirs, Malay bears, ox-like bantengs, deer, crocodiles, elephants in the north, and rhinoceros in the north-west. The lowlands and coastal areas are extremely hot and humid, but the uplands of the interior are moderate in climate and comfortable for Europeans, especially in the north. The November-to-May rainy season brings with it strong winds, which have effects well inland.

Dutch Borneo was divided into the South and East District with its capital at Bandjermasin, and the West District with its capital at Pontianak. The South and East District had a population of 1.4 million, and the West District of 830,000. Dutch administration was not fully established on Borneo until the 1930s. The population included about 6,000 Europeans, 2.1 million islanders of at least six ethnic groups, 140,000 Chinese, and 13,000 other Asians and Arabs.

Three widely separated areas were developed by the Dutch: Balikpapan on the east-central coast for petroleum production, Bandjermasin on the south-central coast for agriculture, and Pontianak on the upper west coast near the border with Sarawak for mining. Dutch Borneo’s only limited road systems were found in these three areas and were not interconnected.

The northern one-third of the island of Borneo was called British Borneo and included North Borneo, a British possession, and Sarawak and Brunei which were both British protectorates ruled by sultans. North Borneo was located on the extreme north-eastern end of the island, and was chartered to the British North Borneo Company in 1881 upon the transfer of the rights originally acquired by an US adventurer in 1865. A British governor administered the colony. The capital was at Sandakan on the north-eastern coast with a population of 13,800 persons. The colony’s population was over 252,000 Malayans and 50,000 Chinese with a small number of Europeans. The main port was at Jesselton on the north-western central coast as was the colony’s only developed road system. The interior is mountainous with a thin coastal strip. The 900 miles (1450 km) of coast are rugged and indented with bays and inlets.

The 35-sq mile (98.4-km²) Labuan island is off of Brunei in the mouth of Brunei Bay. It had been a British possession since 1846, first as part of Singapore but then made a separate colony in 1912 within the Straits Settlements. It had a population of 8,960 Malays, Chinese and a few Europeans. Its capital is Victoria.

Sarawak covers 50,000 sq miles (129500 km²) of Borneo’s north-western coast. A British subject, James Brooks, obtained title to the land from the Sultan of Brunei in 1842, and effectively ruled the land as the 'White Rajah'. In 1888 Sarawak was recognised by the UK as an independent state and granted British protectorate status. Brooks, who was knighted, established the Rajah as a hereditary line and his descendants continued to rule. At the beginning of the war the Rajah was Sir Charles Vyner Brooks represented by a special commissioner. Sarawak’s population was almost 490,600 Europeans, Malays, and Chinese. Most towns and villages lay along the coast with few found inland. The capital was Kuching, with a population of 30,000, and lies 22 miles (35 km) inland on the Sarawak river near the country’s western end. Miri, on the upper north-western coast near Brunei, was the main oil production centre and there was an oil refinery at Lutong. Oil and rubber were Sarawak’s main exports.

Brunei is situated on the upper north-western coast of British Borneo between Sarawak, which had been part of Brunei until 1842, and North Borneo. It covers 2,226 sq miles (5765 km²) and is divided into two separate areas by Brunei Bay; there is no land connection between the two areas. Brunei was ruled by a Moslem sultan under British protection from 1888. A British resident, responsible for administration, was established in 1906. Brunei City, located 20 miles (32 km) inland to the west of Brunei Bay, was the capital with a population of 11,000 persons, and the population of the country was about 39,000 people, most of them Malays. It has a narrow, flat coastal plain with mountains in the east and hilly lowlands in the west. The highest elevation is Bukit Pagon at 6,069 ft (1850 m) in the east. An oilfield was located at Seria on the coast near the Sarawak border. Rubber production was also a major economic resource.

Separately from its oil, rubber and mineral resources, Borneo was strategically important as it lies astride important shipping lanes on all sides: South China Sea, Sulu and Celebes Sea, Straat Makassar, and the Java Sea. Dutch defences on Borneo were virtually non-existent other than some air units at the Singkawang II base on the upper western coast of Kalimantan.

Only at a time late in 1940 did Air Chief Marshal Sir Robert Brooke-Popham, the commander-in-chief of the Far East Command, order the 2/15^th Punjab Regiment, a battery of 6-in (152-mm) heavy guns of Hong Kong-Singapore Royal Artillery, and a detachment of the 35^th Fortress Company (Royal Engineers) to be positioned at Kuching. This garrison force numbered about 1,050 men. In addition, the Brooke government also organised the Sarawak Rangers of 1,515 men mostly of Iban and Dayak tribal origins. Altogether, these forces were commanded by a British officer, Lieutenant Colonel C. M. Lane, and were known as 'SARFOR' (Sarawak Force).

After having heard of the attack on Pearl Harbor, on 8 December 1941, the Brooke government ordered that the oilfields at Miri and Seria, together with the refinery at Lutong, be quickly demolished.

The British possessed only very small garrison and police forces in British Borneo. The Indian troops of the 2/15^th Punjab Regiment defended Kuching, the capital of Sarawak, with a company at Miri. The Sarawak Volunteer Corps (local British volunteers), Sarawak Rangers (native militia), and Borneo police were attached to the Indian battalion. In slightly greater detail, the Dutch forces in West Borneo comprised the West Borneo Garrison Battalion, the Stadswacht Infantry Company (about 125 men) in Pontianak, an anti-aircraft battery (two 40-mm guns and some machine-guns), the Mobile Auxiliary First Aid Platoon, a Stadswacht detachment (about 50 men) in Singkawang and a Stadswacht detachment (unknown strength) in Sintang.

The Dutch had an important airfield near the border with Sarawak, and this Singkawang II, which was defended by about 750 Dutch troops. On 25 November, five Brewster 339 Buffalo single-engined fighters arrived for local defence, followed in the beginning of December by Martin 139 twin-engined bombers. The Dutch navy GVT-1 group, with three Dornier Do 24K twin-engined flying boats, was located in Pontianak along with a land garrison, commanded by Lieutenant Colonel Dominicus Mars and numbering about 500 men.

Otherwise known as the 'Kawaguchi' Detachment, the 35^th Brigade was the core of the Japanese invasion force, together with the 2^nd Yokosuka Special Naval Landing Force. These deployed from Cam Ranh Bay in Japanese-occupied French Indo-China and landed unopposed at Miri on the upper north-western coast of Sarawak and North Borneo on 16 December 1941. The 'Q' (i) forces comprised the headquarters of the 35^th Brigade, the 124^th Regiment detached from the 18^th Division, the 2^nd Yokosuka Naval Landing Force, the 4^th Naval Construction Unit, one platoon of the 12^th Engineer Regiment, one unit of the 18^th Division Signal Unit, one unit of the 18^th Division Medical Unit, the 4^th Field Hospital of the 18^th Division and one unit from the 11^th Water Supply and Purification Unit. The invasion convoy, which had departed Cam Ranh Bay on 13, was escorted by the by the light cruiser Yura flying the flag of Rear-Admiral Shintaro Hashimoto), the destroyers of the 12^th Destroyer Division (Murakumo, Shinonome, Shirakumo and Usugumo), the submarine chaser CH-7 and the seaplane tender Kamikawa Maru. The 10 transport vessels were the Imperial Japanese army’s Katori Maru, Hiyoshi Maru, Myoho Maru, Kenkon Maru and Nichiran Maru, and the Imperial Japanese navy’s Hokkai Maru, Tonan Maru No. 3, Unyo Maru No. 2, Kamikawa Maru and Mitakesan Maru. Heavier naval strength was provided by Rear Admiral Takeo Kurita’s Support Force, which comprised the heavy cruisers Kumano and Suzuya together with the destroyers Fubuki and Sagiri.

As noted above, the oilfields at Miri and Seria in Brunei and the refinery at Lutong had been destroyed before the arrival of the Japanese. On the following day Dutch aircraft began three days of attacks on Japanese shipping. Martin 139 bombers attacked Japanese shipping from their Singkawang II base at Miri on 17 December, but their attempt failed. The three Do 24K flying boats followed with their own attack, but one of the flying boats was shot down, possibly by a floatplane from Kamikawa Maru. The remaining two, benefiting from cloud cover, were not spotted by the Japanese: one of them landed two 441-lb (200-kg) bombs on Shinonome, causing a massive explosion, while a near miss ruptured the destroyer’s hull plating, the destroyer’s stern broke off and the ship sank within minutes' and the other flying boat dropped its bombs on a freighter, but missed. The bombers made attacks at Miri on 18 and 19 December, but were pulled back to Sumatra on 23 December as the Singkawang II airfield had been discovered by the Japanese, who began attacking it the same day.

On 22 December, a Japanese convoy left Miri for Kuching, but was spotted by the Dutch flying boat X-35, which radioed a warning to the Dutch submarine K-XIV. At 20.40 on 23 December, K-XIV worked its way into the convoy and began its attack. The army transports Hiyoshi Maru and Katori Maru were sunk with the loss of hundreds of troops. Hokkai Maru was damaged so severely that she had to be beached to prevent her from sinking, and another transport was less seriously damaged.

The rest of the troops were able to land. Although the 2/15^th Punjab Regiment, resisted the attack, they were soon outnumbered and retreated up the river. By the afternoon, Kuching was in Japanese hands.

On the night of 23/24 December, K-XVI torpedoed the Japanese destroyer Sagiri some 30 miles (48 km) to the north of Kuching, becoming the first Allied submarine in the Pacific War to sink a warship. K-XVI was lost with all hands during the day by a torpedo from the Japanese submarine I-66.

On 24 and 28 December, Dutch bombers from a different unit flew missions against Kuching from Singapore and Sembawang. On 26 December, bombers from Samarinda sank a Japanese minesweeper and a collier.

Despite British and Dutch air attacks and Dutch submarine attacks on the Japanese convoy, on 24 December two battalions of the 'Kawaguchi' Detachment, which had re-embarked two days earlier, landed at Kuching on the western end of Sarawak. The Indian battalion lost two companies attempting to defend the airfield and the survivors were forced to withdraw to Sanggau in Dutch Borneo, and were here placed under Dutch command. The Dutch aircraft at Singkawang II were withdrawn to Sumatra.

On 3 January 1942, the Japanese landed unopposed on Labuan island in Brunei Bay. On 7 January Japanese troops in Sarawak crossed the border into Kalimantan on the western coast and the following day occupied Jesselton in North Borneo. The Royal Air Force ended flights over Borneo from Malaya on 9 January.

(On the other side of Borneo, during 11 January, the 5,500-man 'Sakaguchi' Detachment, comprising the 146^th Regiment of the 56^th Infantry Group, detached from the 14^th Army, under the command of Major General Shizuo Sakaguchi, and elements of the 2^nd Kure Special Naval Landing Force from Mindanao in the Philippine islands group, landed on Tarakan island off the upper eastern coast of Kalimantan at the start of 'B' [ii]. The Japanese landed on the island’s eastern coast, opposite the Dutch defences on the other end of the island, and seized the oil field and airfield. The island was defended by the Dutch 7^th Garrison Battalion plus artillery and anti-aircraft troops with a strength of 1,300 men. The garrison surrendered on the following day after a brief but stout resistance, and more than 250 Dutch soldiers were murdered for their resistance, most by drowning, by order of Sakaguchi.)

On the next day, Japan declared war on the Netherlands East Indies. The Japanese landed at Sandakan in North Borneo on 17 January, and the capital surrendered on the next day, and on 19 January North Borneo surrendered.

(On 23 January units of the 'Sakaguchi' Detachment and elements of the 2^nd Kure Special Naval Landing Force landed unopposed at Balikpapan on the east-central coast in an expansion of 'B' [ii]. The 1,100 Dutch troops of the 6^th Garrison Battalion plus artillery and anti-aircraft units had destroyed the oil installations before the Japanese landed. Some of the garrison was evacuated, but most were forced to surrender after only minimal resistance, and 80 soldiers and civilians were murdered by the Japanese in reprisal for burning the oil facilities. On the next day the Japanese discovered the secret Samarinda II airfield to the north of Balikpapan near inland Longiram and began air attacks. The few remaining aircraft were evacuated on 28 January, but the 500-man garrison remained to await the expected arrival of US aircraft. When these latter failed to appear most of the garrison attempted to organise themselves fore continued operations as guerrillas, but the Japanese paid Dayak indigenous people to hunt them down, with many murdered over the next months.)

At about 16.40 on 25 December, Japanese troops captured Kuching’s airfield. The Punjab regiment retreated through the jungle to the Singkawang area. After Singkawang was lost on 29 December, the rest of the British and Dutch troops retreated southward farther into the jungle, trying to reach Sampit and Pangkalanbun, where a Dutch airfield was located at Kotawaringin. On 29 January a Japanese force from Sarawak occupied Pontianak on the west-central coast. By 13 February Bandjermasin on the south-eastern end of Borneo had been occupied by a battalion of the 'Sakaguchi' Detachment moving overland from Balikpapan. The 500-man Dutch garrison attempted to destroy facilities of use to the Japanese, but most of the Indonesian troops deserted. Borneo was secured by the Japanese, who planned to develop it as an economic base, especially for the exploitation of its oil and other natural resources. Crews of technicians and labourers had been prepared for he rapid repair of the oil production facilities and restore them to operation.

After 10 weeks in the jungle-covered mountains, the last surviving Allied troops surrendered on 1 April 1942.