Leslie George Cairns was born in Stirling, 4 April 1920. he attended Newstead School, Doune, Perthshire, and then read History at Edinburgh University, 1937-1940. He joined the Army in 1940 having been granted a War Honours degree on the strength of classes attended and his performance. While at University he had been a member of the Edinburgh University Officer Training Corps (EUOTC), and he was commissioned into the Royal Artillery.
During the Second World War, Cairns served with the Ayrshire Yeomanry on British soil and then with the 11th Field Regiment in North Africa (at El Alamein and at the Mareth Line). He then transferred to the Parachute Regiment and then to the Special Air Service Regiment, Army Air Corps (SAS).
Leslie George Cairns was posted missing, presumed killed in action, on 18 June 1944. he and all his 15 men disappeared, with the aircrew of 6, when on a secret mission to central France.
Earlier, in 1943, he had married Irene J. Young. Her book Enigma Variations: a Memoir of Love and War (1990) chronicles the relationship and the times.