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 unit, 23rd Brigade Signals unit and the 2/11th Field Company.
Sparrow Force were reinforced on the 16 February 1942 with 189 British anti-aircraft gunners, from A & C troop of the 79th Light Anti-Aircraft Battery of the Royal Artillery, mostly veterans of the Battle of Britain. Further reinforcements, an Australian infantry battalion and an American artillery regiment, were attacked en-route to Timor and returned to Darwin.
The 2/40th and most Sparrow Force units were based at Penfui Airfield, outside the capital of Netherlands Timor, Kupang. The 2/2nd Independent Company was based across the border, at Dili in Portuguese Timor.
While withdrawing from Kupang towards Portuguese Timor, the main body of Sparrow Force encountered 500 Japanese marine paratroopers, who had landed near Babau and at Usua Ridge, on 21-22 February 1942. The Japanese were dug in to a defensive position at the top of Usua Ridge. After an Australian mortar barrage, Leggatt led his battalion in a bayonet charge up the ridge, effectively destroying the paratroopers as a fighting force. However, Sparrow Force was attacked from the west by the main Japanese force. The following day, with his men low in ammunition and hopelessly outnumbered, Leggatt surrendered at Airkom on 23 February.
Some members of Sparrow Force who were in Netherlands Timor, but were not in the main column at Airkom, escaped to Portuguese Timor where they joined the 2/2nd Independent Company. They commenced a successful guerilla campaign against the Japanese Imperial Army until their eventual withdraw in December 1942.
Between the surrender at Airkom and April 19 1942 the communication link with the Australian mainland was broken. Captain George Parker, Signaller Keith Richards, Cpl John Donovan, Signaller Jack Loveless and Sgt Jack Sargeant built a radio out of recycled parts and re-established contact with Darwin. Supplies were soon airdropped to the guerilla force.
The Japanese High Command diverted an entire division to flush out the guerillas of Sparrow Force. A highly-decorated Japanese Major known as the "Tiger of Singapore" or "Singapore Tiger" — his real name is unknown — was also sent to Timor. Shortly after arrived on Timor, on 22 May a Japanese party was moving on Remexio and an Australian patrol with the international brigade staged an ambush killing 4 or 5 Japanese soldiers and another ambush further down the track killing another 25 Japanese. In the second ambush Cpl Aitken and his patrol saw the "Tiger", wearing his medals, on a white horse leading the enemy column. The Tiger was killed and the Japanese retreated to Dili.
The Allied guerillas would become associated with the phrase "you alone do not surrender to us", which were contained in a message to the men of Sparrow Force by the Japanese commander on Timor, Lieutenant General Yuichi Tsuchihashi. Winston Churchill later stated: "they alone did not surrender."
In late 1942, Army public relations sent the Academy Award winning filmmaker Damien Parer, and war correspondent Bill Marien to Timor, to record the efforts of the Australian commandos. His film Men of Timor was greeted with enthusiasm by Australian audiences.
In September 1942, Sparrow Force was reinforced by the Australian 2/4th Independent Company (Lancer Force). With the exception of a few officers, Sparrow Force was evacuated to Australia on December 11-12.
Of those evacuated, the 2/2nd Independent Company was renamed the 2/2 Commando Squadron and fought in New Guinea and New Britain ending the war in Rabaul. Of the 81 members of the 2/40 Infantry Battalion evacuated, many soldiers reinforced the Tasmania/Queensland-raised 2/12th Infantry Battalion, in the Australian 7th Division, which later fought in the Salamaua-Lae campaign, the Finisterre Range campaign and the Borneo campaign (1945). By the end of the war "2/2 Commando Squadron could claim to have spent longer in contact with the enemy than any other unit of the Australian Army" (Grant 2005).