The Japanese invasion of West Timor in the Netherlands East Indies and the adjacent Portugese East Timor marked the southernmost limit of their occupation of south-east Asia.
Just days after the Japanese attack on Pearl Harbor in December 1941 a force of 1400 Australians known as Sparrow Force landed in Timor. Although Dutch and British officials had agreed that Allied troops under Australian command would support the small Dutch and Portuguese garrisons there, the Portuguese officially maintained their neutrality.
The Australians, under the command of Lieutenant-Colonel William Leggatt, included the 2/40th Battalion from the 8th Division as well as the 2/2nd Independent Company and other detachments. Once in Timor, Sparrow Force divided. The 2/40th Battalion remained around Koepang in the Dutch zone on the south-west of the island to defend the bay and nearby Penfui airfield where a flight of Hudson bombers of 2 Squadron RAAF was based. The 2/2nd Independent Company went to the Portuguese zone setting up base at Dili, the administrative capital, on the north coast of Timor.
The airstrip at Penfui was an important point in the air route between Australia and General Douglas Macarthur's American forces in the Philippines. It was also an important air link in the 'Malay Barrier'. Japanese air raids on the airfield on 26 and 30 January 1942 encouraged the Australian government to make preparations for reinforcements to be sent to Timor. Their arrival was delayed when the convoy, which included the destroyers HMA Ships Swan and Warrego, was intercepted by Japanese bombers and forced to return to Darwin. Additional headquarters staff for Sparrow Force under Brigadier William Veale arrived in Koepang on 12 February.
By 19 February it was clear that the Japanese invasion was imminent and the surviving aircraft of 2 Squadron RAAF, which had flown several missions against Japanese bases and shipping, were despatched to Darwin. That same day, six of the squadron's Hudsons were destroyed in the Japanese bombing raid on Darwin. By then it was too late to evacuate the troops of Sparrow Force so they stayed on the island.
The Japanese attacked Dili about midnight on 19-20 February and the 2/2nd Independent Company was able to inflict some damage on Japanese troops before withdrawing into the hinterland. Other Japanese forces came ashore at Koepang where the Australians fought valiantly but Sparrow Force was split by the Japanese advance. In West Timor Leggatt's men, many of them sick or wounded, were short of ammunition, food and water. They fought a far superior force for four days but the Japanese were systematically overrunning their positions when Leggatt surrendered with his 1123 men on 23 February.
Brigadier Veale and a group of about 250 men in West Timor were able to withdraw east and join the 2/2nd Independent Company in East Timor where they began a guerrilla warfare campaign. The independent company troops were specially trained for commando-style operations, and they became the only Australian force still in action in enemy territory after the Japanese conquest of south-east Asia.
During the early months, the success of the guerrillas in East Timor was only made possible by the support they received from the local Timorese who, risking execution by the Japanese, acted as porters and guides and provided food and shelter. In April, the force was able to communicate with Australian authorities for the first time. Some of the men had constructed an improvised radio set, 'Winnie the War Winner', named after the British Prime Minister, Winston Churchill, and within 48 hours of making contact with Darwin they received much needed supplies and directions to continue their campaign.
During the following months the guerrillas inflicted damage on the Japanese occupation forces wherever and whenever they could. However, in August the Japanese launched a major counter-offensive destroying many of the links between the Australians and the local people. Although some of the Timorese were still prepared to risk their lives helping the Australians, it became more and more difficult for the guerillas to operate.
The RAAF and RAN continued supporting Sparrow Force with regular air drops and supply voyages. In September 1942, 450 troops of the 2/4th Independent Company were landed from the destroyer HMAS Voyager. The ship ran aground in Betano Bay and was scuttled. In November, it was decided to relieve the weary 2/2nd Independent Company by evacuating them by ship. On 1 December, the corvette HMAS Armidale was sunk south of Timor while delivering Dutch colonial troops as part of the relief effort. Most of the crew and all of the troops were lost. The 2/2nd troops were withdrawn later that month.
Sparrow Force operations on Timor were progressively wound down. The Japanese, determined to wipe out the guerrillas, reinforced their garrison, with stronger patrols into the hinterland. In February 1943, the remaining members of Sparrow Force were withdrawn from East Timor. Australian and American aircraft continued bombing Japanese bases but the guerrilla campaign itself was at an end.