 The plans for the invasion of Borneo evolved considerably during April . Initially , the offensive was to commence on 23 April with the landing of a brigade from the 6th Division on the island of Tarakan , off the east coast of Borneo . The 9th Division would then assault Balikpapan followed by Banjarmasin in south @-@ east Borneo . These positions would be used to support the invasion of Java by the remainder of I Corps . After the attack on Java was cancelled , it was decided to employ two brigades of the 7th Division at Brunei Bay , and I Corps conducted further preparations on this basis . However , on 17 April General Douglas MacArthur 's General Headquarters ( to which I Corps reported ) swapped the roles of the 7th and 9th Divisions . Accordingly , the final plan for the attack against Borneo specified that one of the 9th Division 's brigades would land on Tarakan island on 29 April ( later postponed to 1 May ) , with the remainder of the division to invade the Brunei Bay area on 23 May . The 7th Division was scheduled to assault Balikpapan on 1 July . The Borneo campaign was designated the " Oboe " phase of the Allied offensive through the southern Philippines towards the Netherlands East Indies , and the landings at Tarakan , Brunei Bay and Balikpapan were designated Operations Oboe One , Six and Two respectively . 
