by Jack McKillop
Physical Description & History
Borneo, the third largest island in the world, is located in the Southwest Pacific south of the Philippine Islands, west of Celebes Island, north of Java and east of Malaysia. The island extends north to south from 6°57'N, 117°07'E to 4°17'S, 114°39'E and has a land area of 287,001 square-miles (743,329 square-kilometers).
Borneo lies on the Equator and has a tropically hot and humid climate along the coast. The temperatures remain fairly constant throughout the year and average about 80°F (27°C). Annual rainfall averages from 100- to 160-inches (2.5- to 4.1-meters) with most of the rain falling during two monsoon seasons.
Most of the island is covered by tropical rain forests, with numerous vines, flowering plants, and dense undergrowth. The coast is a low, largely marshy belt, 10- to 50-miles (16- to 80-kilometers) wide, which contains large areas of mangrove swamp. The interior is predominantly mountainous, with peaks up to about 8,000-feet (2,438-meter).
Oil was discovered on Borneo in 1910 and by 1940, large oil fields were in production at Miri, Seria, and Lutong in or near Brunei on the northwest coast; at Sandakan, Tarakan, and Balikpapan along the east coast; and at Kuching and Pontianac on the west coast. Borneo crude oil was light enough to be burned directly in ship's boilers, without refining, but when the Japanese turned to this expedient late in the war, they found that the sulfur content was high enough to make boiler steel brittle, eventually ruining the boilers.
In December 1941, Borneo was divided into four political subdivisions; three of them on the northwest were British protectorates but 73 percent of the island was part of the Netherlands East Indies (NEI) under Dutch administration. The four subdivisions of Borneo were:
After the Germans conquered The Netherlands in 1940, the NEI government remained loyal to the Dutch government in exile. By January 1941, the Japanese were demanding more of the products produced in the NEI but they were only receiving 51.7 percent of the oil, 61 percent of the bauxite and 83 percent of the nickel that they wanted. In addition to these, the NEI also produced rubber, copra, timber, quinine, sugar, rice, tea and coffee. The Japanese demands increased and the NEI government finally stopped supplying oil to Japan in August 1941. After the Japanese captured Borneo in 1941-1942, it was estimated that the oilfields of Borneo provided 40 percent of the fuel oil and 25 to 30 percent of the crude and heavy oil used by the Japanese.
Balikpapan, Naval Advance Base
Balikpapan (1°16'S, 116°50'E), the largest city in Dutch Borneo, is a seaport city on the east coast of Dutch Borneo. The city is on the Sumbir River on the southeast coast and boasted a significant oil field (7.4 million barrels a year) and a refinery and a newly constructed port with just enough facilities to load tankers.
The Japanese Army landed at Balikpapan on 23 January 1942. The next day, the Battle off Balikpapan (also known as the Battle of Makassar Strait) occurred when four USN destroyers attacked the Japanese Borneo invasion convoy. The destroyers sank three transports, a cargo ship and a patrol boat while U.S. Army Air Forces (USAAF) B-17 Flying Fortresses and Dutch Martin 139s and Brewster 339s sank two transports.
Bombing missions against Balikpapan by the USAAF began in August 1943 and occasionaly thereafter. Starting in May 1945, the USAAF’s Thirteenth Air Force flew at least one mission a week until June when they began daily missions by bombers and fighters. After the Allies invaded the area they flew missions in support of the ground forces.
On 15 June 1945, 15 USN motor minesweepers (YMS), accompanied by the high speed transport USS Cofer (APD-62) and landing craft equipped with light minesweeping gear, arrived off Balikpapan to begin mine clearance operations. Ten days later, underwater demolition teams (UDTs), covered by aircraft, begin operations on the beaches at Balikpapan in advance of landings slated to begin there.
On 1 July, the USN landed elements of the 7th Australian Division (Reinforced), less one brigade, at Balikpapan. The landing was covered by Allied naval gunfire and aircraft. This, the final major amphibious assault of World War II, was unopposed. The next day, the Australians took Balikpapan and its oil installations and subsequently extended their holdings in this area. Three days later, the Australian troops crossed Balkipapan Bay and landed on the western shore without opposition and by 9 July, they had completed the encirclement of the Bay. The area was considered secure by the end of July.
Supporting the operation were the motor torpedo boat tenders USS Mobjack (AGP-7) and USS Varuna (AGP-5) tending 19 motor torpedo boats (PTs) of two PT squadrons. Prior to the invasion, the PT boats were assigned to night patrol off the coast to prevent the Japanese from replacing naval mines, restoring obstacles blown by underwater demolition teams, or disturbing channel markers planted by the minesweepers.
Navy Seabees also landed to operate three pontoon causeways established at Balikpapan, over which both supplies and personnel were landed. They also operated five strings of pontoons at the landing beach near the Sepinggang airfield (1°16' 06"S, 116°53' 40"E), now Sepinggan International Airport, 5-miles (8-kilometers) east of Balikpapan. They also set up a ship-repair unit which serviced 16 tank landing craft (LCTs) in the first 11 days.
Facilities for servicing the PT boats were also built. These boats patrolled Makassar Strait up to the west coast of Celebes Island, 170-miles (274-kilometers) to the southeast. They also engaged in harassing activities against the Japanese ground forces.
After the Japanese surrender, naval forces here assisted freed Allied prisoners of war and refugees. The last PT squadron was decommissioned on 11 November and Naval Advance Base Balikpapan was closed in December.
Brunei Bay, Naval Advance Base
The capital of Brunei, Brunei Town (now Bandar Seri Begawan), is on the western shore of Brunei Bay. The city was occupied by the Japanese on 22 December 1941.
On 10 June 1945, troops of the 9th Australian Division landed in Brunei Bay (4°57'N, 115°06'E) on the northwest coast of British North Borneo. The bay covers approximately 500 square-miles (1,295 square-kilometers) and is an excellent protected anchorage. Participating in the invasion were motor torpedo boat tender USS Willoughby (AGP-9) and 17 motor torpedo boats (PTs) of two PT squadrons. The PT boats patrolled the invasion area during the night.
B-24 Liberators of the U.S. Army Air Forces’ Thirteenth Air Force bombed the Brunei Bay area twice in November 1944. Ten additional missions were flown in May and June 1945 prior to the invasion by the Royal Australian Air Force (RAAF) and the USAAF.
After the invasion, U.S. Navy Seabees landed and constructed port director facilities and a PT boat base on Muara Island (5°00'N, 115°06'E) in the bay. The PT boats patrolled the area but as targets disappeared, they then machine-gunned and mortared Japanese positions, and at times conducted joint strikes with RAAF aircraft at Jesselton, Miri, and Kudat, three Japanese-held oil centers on North Borneo.
After the Japanese surrender, the PT boats evacuated 210 Allied prisoners of war and women and children prisoners and transferred them to the USS Willoughby or the Australian hospital ship Manunda.
The two PT squadrons were decommissioned in November 1945 and the port director’s facility was closed on 27 January 1946.