Completing his service with No. 21 Squadron in November 1941, Jackson was again posted to No. 23 Squadron in Australia. In March 1942, he joined No. 75 Squadron in New Guinea as a flight lieutenant, under the command of his brother, known as "Old John".Gillison, Royal Australian Air Force 1939–1942, pp. 458–461 Operating P-40 Kittyhawks, the unit quickly became engaged in the defence of Port Moresby, one of the crucial early battles in the New Guinea campaign.Stephens, The Royal Australian Air Force, pp. 139–141 As one of No. 75 Squadron's flight commanders, Jackson took part in a surprise raid against Lae airfield on 22 March. Five Kittyhawks led by John Jackson attacked and destroyed a dozen Japanese planes on the ground, while four others including Les provided protective cover above; he survived an encounter with three Mitsubishi Zeros that saw two of his fellow pilots shot down. Two days later he recorded his first aerial victory when he intercepted and destroyed a Zero escorting a force of bombers towards Port Moresby.
