The Japanese had seized North Borneo early in the Pacific War, capturing the territory's vital oilfields. By 1943, those fields were fueling the Japanese war effort, and Allied efforts to stop the flow had been limited mostly to aerial bombing. Planning for covert operations in Borneo stretched back to December 1941, when a British intelligence officer named Second Lieutenant P. M. Synge proposed inserting a small team to organize guerrilla resistance. His plan was shelved, but the idea persisted. By 1945, Australia's Services Reconnaissance Department launched Operation Agas alongside a companion operation called Semut in neighboring Sarawak. Five separate Agas missions would follow between March and August 1945, involving a total of 44 personnel operating across the breadth of North Borneo.

Agas 1 established a signals station at Lokopas and a hospital on Jambongan Island, collecting intelligence on Japanese train schedules, cargo movements, and troop positions around Sandakan. Agas 2, a five-man team led by Major R. G. P. N. Combe, parachuted into Paitan Bay in May to support the planned Australian assault on Brunei Bay and Labuan, setting up guerrilla operations around Banggi Island and Marudu Bay. Agas 3, also led by Chester, focused on the Jesselton-Keningau-Beaufort corridor but faced stiff resistance -- up to 6,000 Japanese troops occupied that sector, and local Chinese communities refused cooperation out of fear of reprisals following the failed 1943 Jesselton Revolt. Agas 4 arrived by PT boat at Semporna in July, and Agas 5 pushed into the area north of Darvel Bay in August, both collecting information on Japanese forces around Tawau and Lahad Datu.

The operations estimated Japanese troop strength at 31,000 in May 1945, remarkably close to the official figure of 35,000 confirmed in October. More critically, Agas provided the intelligence that Japanese forces intended to evacuate the coast and withdraw into the North Borneo interior -- information that directly influenced Allied planning for Operation Oboe Six, the Battle of North Borneo. Agas 1 also relayed information about the Sandakan Death Marches, though no rescue missions were launched for the prisoners of war. The intelligence guided successful bombing raids on Sandakan instead. Across the five operations, the teams trained roughly 250 local guerrillas and established hospitals that treated more than 2,000 local inhabitants.

Historian Alan Powell assessed that "Agas succeeded politically" but "had little direct military value and failed as a POW rescue operation." The guerrilla forces, scarred by the brutal Japanese reprisals after the 1943 Jesselton Revolt, were reluctant to launch major attacks. Around 100 Japanese soldiers were killed by Agas-recruited fighters -- a modest tally. But the operation's real contribution was strategic: the intelligence it produced helped the Allies avoid costly direct assaults and plan a more effective liberation campaign. After hostilities ended, Australian troops remained in North Borneo to restore order, rebuild infrastructure, establish schools, and provide medical care. The 44 men of Operation Agas had been, in the most literal sense, sandflies -- small, persistent, and impossible for the occupiers to ignore.