Early in the Pacific War, the Japanese had landed in north-west Borneo and had quickly captured the area's vital oilfields, which had begun contributing to their war effort by 1943. Allied efforts to interdict the flow of oil had been limited largely to aerial bombing in the intervening period as Allied ground efforts had focussed upon the drive on the Philippines. Nevertheless, by late 1944 – early 1945 the Allies had begun planning operations to retake the area. Allied operations to re-capture Labuan and Brunei Bay were scheduled for mid-June 1945. To support this, Operation Agas was launched in March 1945 by Australian Services Reconnaissance Department (SRD), utilising Z Special Unit personnel. The operation had two main objectives: to gather intelligence and to train the indigenous people to undertake a guerrilla campaign against the Japanese. Subsequently, a series of five operations were undertaken in the Japanese occupied areas of North Borneo in the final stages of the war under the auspices of Operation Agas – the Malay word for sandfly – which were undertaken in conjunction with Operation Semut in Sarawak. The Japanese troops occupying north Borneo at the time were drawn from the 37th Army.