Cairns was awarded the Distinguished Conduct Medal (DCM) for his actions at the Battle of Vimy Ridge in April 1917.

He was 21 years old, and a sergeant in the 46th (South Saskatchewan) Battalion, Canadian Expeditionary Force during the Hundred Days Offensive of the First World War when the following deed took place for which he was awarded the VC.

Later, when the line was held up by machine-gun fire, he again rushed forward, killing 12 enemies and capturing 18 and two guns.

Throughout the operation, he showed the highest degree of valour, and his leadership greatly contributed to the success of the attack.

[4]With the German surrender and armistice on 11 November, ten days later, Sergeant Cairns would prove to be the last of seventy-one Canadians to earn the Victoria Cross for his actions in the Great War.

[5] In March 1936, the town of Valenciennes renamed a street in the vicinity of his actions on 1 November 1918 "Avenue du Sergent Cairns"[1] and a plaque commemorating his valorous actions was installed on the side of a building opposite the Place du Canada on the street that bears his name.