Leslie spent the first 6 months of his captivity in Changi, but was then shipped to Borneo as part of 'D' Force to build an aerodrome at Sandakan. He recalled the appalling conditions of both the ship and the new campsite, to which the prisoners were sent and which they virtually had to build from scratch.

Leslie received a serious neck injury when he was struck by a Japanese officer armed with a wooden changkol handle. Bashings were a regular part of prison camp life at the aerodrome and also in the Kuching camp.

Leslie thought of the mateship displayed by the men as being something close to a brotherhood. As an officer, he was mindful of providing guidance to the men. Morale in the camp was maintained through the presentation of concerts and the use of a secret radio, which brought news in from the wider world.

For Leslie, the best part of the war was his return to Australia. He discharged from the army on 19 December 1946.