Credited with a fifth aerial victory, he became the RAAF's first ace in the New Guinea campaign, and was awarded the Distinguished Flying Cross (DFC).

[7] 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.

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.

[4][7] On 6 April, Jackson was forced to ditch his aircraft on a coral reef, but made it to shore with the aid of a life jacket that his brother John dropped to him.

On 5 April, he was attacked from behind by a Zero while firing on bombers front-on, but was able to turn the tables on the Japanese fighter and shoot it down in flames.

[4][12] On 30 April, the squadron was recalled to Australia to refit and regroup; Jackson flew one of its last remaining serviceable aircraft to Cairns, Queensland, on 9 May.

[13] During the Battle of Milne Bay, Jackson's squadron was engaged in air defence against Japanese raiders and offensive strikes against convoys and other targets in support of Australian ground forces.

On 25 August, the Kittyhawks launched an attack on enemy barges at Goodenough Island that resulted in all seven vessels being set on fire without the loss of any aircraft.

[14] The next day, Jackson personally led two of his unit's five concerted strafing assaults on the main Japanese convoy approaching Milne Bay.

[16] By 28 August, Japanese troops were threatening to overrun the RAAF airfield at Milne Bay, and the Kittyhawk squadrons were ordered to withdraw to Port Moresby for one night.

[2][15] By 7 September the Japanese had withdrawn their troops from the Milne Bay area; Generals Sydney Rowell and Cyril Clowes both described the efforts of Nos.

[18][19] In recognition of his "courage and leadership" in New Guinea, Jackson was awarded the Distinguished Flying Cross (DFC), which was promulgated in the London Gazette on 26 March 1943.

[1][22] The wing participated in Operations Reckless and Persecution, the assault on Hollandia and Aitape that opened the Western New Guinea campaign, in April 1944.

[1][24] Jackson continued to lead Air Defence Headquarters in Madang following the end of hostilities, before his commission was terminated in Brisbane on 8 February 1946.

He married Cynthia Molle at St Andrew's Presbyterian Church, Southport, on 25 January 1947; the couple had three sons.