Indonesia Malaysia confrontation People and terrain

In 1961, the island of Borneo was divided into four separate states. Kalimantan, comprising four Indonesian provinces, was located in the south of the island. In the north, separated from Kalimantan by a border some 1000 miles long, were the Sultanate of Brunei (a British protectorate) and two colonies of the United Kingdom (UK)—Sarawak and British North Borneo (later renamed Sabah).

The three UK territories totalled some 1.5 million people, about half of them Dayaks. Sarawak had a population of about 900,000, while Sabah's was 600,000 and Brunei's was around 80,000. Among Sarawak's non-Dayak population, 31% were Chinese, and 19% were Malay. Among non-Dayaks in Sabah, 21% were Chinese and 7% were Malay; Brunei's non-Dayak population was 28% Chinese and 54% Malay. There was a large Indonesian population in Tawau in southern Sabah and a large and economically active Chinese one in Sarawak. Despite their population size, Dayaks were spread through the country in village longhouses and were the not politically organised.

Sarawak was divided into five administrative Divisions. Sabah, whose capital city was Jesselton (Kota Kinabalu) on the north coast, was divided into several Residencies; those of the Interior and Tawau were on the border.

Apart from either end, the border generally followed a ridge line throughout its length, rising to almost 2500 metres in the Fifth Division. In the First Division, there were some roads, including a continuous road from Kuching to Brunei and around to Sandakan on the east coast of Sabah. There were no roads in the Fourth and Fifth Divisions or the Interior Residency, and in Third Division, there was only the coast road, which was some 150 miles from the border. Mapping was generally poor, as British maps of the country showed very little topographic detail. Indonesian maps were worse; veterans recall “a single black and white sheet for all of Kalimantan torn from a school text book” in 1964.

Kalimantan was divided into four provinces, of which West Kalimantan (Barat) and East Kalimantan (Timur) face the border. The capital of the first is Pontianak on the west coast, about 100 miles from the border, and the capital of the East is Samarinda on the south coast, some 220 miles from the border. There were no roads in the border area other than some in the west, and no road existed linking West and East Kalimantan.

The lack, on both sides of the border, of roads and tracks suitable for vehicles meant that movement was limited to foot tracks mostly unmarked on any map, as well as water and air movement. There were many large rivers on both sides of the border, and these were the main means of movement, including Hovercraft by the UK. There were also quite a few small grass airstrips suitable for light aircraft, as dropping zones for parachuted supplies, and for helicopters.

The equator lies 100 miles south of Kuching, and most of northern Borneo receives over 3000 mm of rain each year. Borneo is naturally covered by tropical rainforest. This covers the mountainous areas cut by many rivers with very steep sided hills and hilltop ridges often only a few metres wide. The high rainfall means large rivers; these provide a main means of transport and are formidable tactical obstacles. Dense mangrove forest covering vast tidal flats intersected with numerous creeks is a feature of many coastal areas, including Brunei and either end of the border. There are cultivated areas in valleys and around villages. The vicinity of abandoned and current settlements are areas of dense secondary regrowth.