Additional Australian support staff arrived at Kupang on 12 February, including Brigadier William Veale, who had been made the Allied commanding officer on Timor. By this time, many members of Sparrow Force—most of whom were unprepared for 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, but 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. Composition The majority of Sparrow Force personnel were from the 2/40th Infantry Battalion, which had been formed in Tasmania and was part of the 23rd Australian Infantry Brigade. The force was initially commanded by Lieutenant Colonel William Leggatt, although later command was taken over by Brigadier William Veale before being passed on to Lieutenant Colonel Alexander Spence. A commando unit—the 2/2nd Independent Company (recruited mostly in Western Australia)—was also part of Sparrow Force. With the other forces from the 23rd Brigade, it shared contingents from 18 Anti-Tank Battery, the 2/12th Field Ambulance, 23rd Brigade Signals and the 2/11th Field Company. Zealandia departed Darwin on the morning of 10 December 1941 with 957 troops escorted by HMAS Westralia with another 445 troops reaching Koepang on 12 December. Rabaul fell to the Japanese on 23 January, followed by Ambon on 3 February, and both Gull Force and Lark Force were destroyed. Sparrow Force was reinforced on 16 February 1942 with 189 British anti-aircraft gunners, from A & C Troops of the 79th Light Anti-Aircraft Battery of the Royal Artillery, most of whom were veterans of the Battle of Britain. They were attacked by Japanese bombers as their ship anchored at Tenau. Later that day, 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 US 49th 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