of Sparrow Force—most of whom were unused to tropical conditions—were suffering from malaria and other illnesses. The airfield at Penfui in Dutch Timor also became a key air link between Australia and American forces fighting in the Philippines under General Douglas MacArthur. Penfui came under attack from Japanese aircraft on 26 and 30 January 1942, however the raids were hampered by the British anti-aircraft gunners and, to a lesser degree, by P-40 fighters of the 33rd Pursuit Squadron, United States Army Air Forces, 11 of which were based in Darwin. Later, another 500 Dutch troops and the British 79th Light Anti-Aircraft Battery arrived to reinforce Timor, while an additional Australian-American force was scheduled to arrive in February. Meanwhile, Rabaul fell to the Japanese on 23 January, followed by Ambon on 3 February, and both Gull Force and Lark Force were destroyed. Later, on 16 February, an Allied convoy carrying reinforcements and supplies to Kupang—escorted by the heavy cruiser , the destroyer , and the sloops and —came under intense Japanese air attack and was forced to return to Darwin without landing. The reinforcements had included an Australian pioneer battalion—the 2/4th Pioneer Battalion—and the 49th American Artillery Battalion. Sparrow Force could not be reinforced further and as the Japanese moved to complete their envelopment of the Netherlands East Indies, Timor was seemingly the next logical target. Battle Japanese invasion of Portuguese Timor, 19–20 February 1942 On the night of 19/20 February 1,500 troops from the Imperial Japanese Army's 228th Regimental Group, 38th Division, XVI Army, under the command of Colonel Sadashichi Doi, began landing in Dili. Initially, the Japanese ships were mistaken for vessels carrying the foreseen Portuguese reinforcements, and the Allies were caught by surprise. Nevertheless, they were well-prepared, and the garrison began an orderly withdrawal, covered by the 18-strong Australian Commando No. 2 Section stationed at the airfield. According to Australian accounts, the commandos killed an estimated 200 Japanese in the first hours of the battle; the Japanese army recorded its casualties as only seven men, but native accounts of the landings support the Australian claims. Another group of Australian commandos, No. 7 Section, was less fortunate, driving into a Japanese roadblock by chance. Despite surrendering, according to military historian Brad Manera all but one were massacred by the Japanese. Outnumbered, the surviving Australians withdrew to the south and to the east, into the mountainous interior. Van Straten and