made an inspection tour of Tarakan on 8 May. During a meeting with Whitehead, Blamey directed that the 26th Brigade Group should "proceed in a deliberate manner" in clearing the rest of the island now that the main objectives of the invasion had been completed. Securing the interior In order to secure the island and protect the airstrip from attack, the 26th Brigade Group was forced to clear the Japanese from Tarakan's heavily forested hills. Approximately 1,700 Japanese troops were dug into positions in the north and centre of the island. These positions were protected by booby traps and mines. While attacking these positions necessarily entailed costly infantry fighting, the Australian troops made heavy use of their available artillery and air support to minimise casualties. The Australian tanks could only provide limited support to the infantry as Tarakan's thick jungle, swamps and steep hills often confined their movement to tracks and roads. As a result, tanks generally could not be used to spearhead attacks, and their role was limited to providing supporting fire for infantry assaults, with artillery being the preferred source of direct support. The 2/3rd Pioneer Battalion and the NEI company were assigned responsibility for securing the south-eastern portion of Tarakan. The pioneers began advancing east of Tarakan Town on 7 May but encountered unexpectedly strong Japanese resistance. From 10 May, the battalion was halted at the 'Helen' feature, which was defended by about 200 Japanese troops. On 12 May Corporal John Mackey was killed after capturing three Japanese machine gun posts. Mackey was posthumously awarded the Victoria Cross for this act. During the fighting at 'Helen' B-24 Liberator heavy bombers were used for close air support for the first time, with P-38 Lightning fighters dropping napalm immediately after the bombing. This combination proved particularly effective, and became the standard form of air support requested by the Australians. The Japanese force withdrew from 'Helen' on 14 May after suffering approximately 100 casualties, and the 2/3rd Pioneer Battalion reached Tarakan's eastern shore on 16 May. The battalion suffered 20 killed and 46 wounded in this operation. During this period the NEI company secured the remainder of southern Tarakan, and encountered little resistance during its advance. The United States and Australian navies continued to support the invasion once the landing was complete. USN PT boats sank at least a dozen small craft off Tarakan and in rivers on the coast