 In March 1945 the Australian Army 's I Corps , whose main combat elements were the veteran 7th and 9th Divisions , was assigned responsibility for liberating Borneo . Planning for the offensive was undertaken over the following weeks . While invading the Brunei Bay area did not form part of the initial iteration of the plans , it was added in early April after a proposed landing on Java was cancelled . The main purpose of attacking Brunei Bay was to secure it as a base for the British Pacific Fleet ( BPF ) , and gain control of oil fields and rubber plantations in the area . Labuan was to be developed as an air base and form part of a string of strategic positions which would allow the Allies to control the seas off the Japanese @-@ occupied coast between Singapore and Shanghai . 
