[3] Leask joined the British Army soon after the outbreak of the First World War, being commissioned as a temporary second lieutenant in the 11th Battalion, Devonshire Regiment on 19 November 1914,[4] just after his 18th birthday.
[2] He was appointed a flight commander with the temporary rank of captain on 10 January 1917,[8] and in May he returned to England to serve as an instructor.
[2] Flying a S.E.5a, Leask gained his first aerial victories on 21 October 1917, when he and John Steele Ralston drove down out of control a German Type C reconnaissance aircraft east of the Roulers–Menin road, and twenty minutes later Leask drove down an Albatros D.V solo.
[9] His citation, published on 23 August, read: Second Lieutenant (Temporary Captain) Kenneth Malise St. Clair Graeme Leask.
For conspicuous gallantry and devotion to duty in leading offensive patrols against superior numbers of the enemy.
His citation read: Second Lieutenant (Temporary Captain) Kenneth Malise St. Clair Graeme Leask, MC, Devonshire Regiment and Royal Flying Corps.
He has done splendid work in attacking enemy troops from a low altitude, showing great courage, and determination under heavy fire.
[13] On 3 July 1920, during the Royal Air Force Aerial Pageant at Hendon Aerodrome, Leask took part in a mock aerial combat in which his Bristol F.2 Fighter was pitted against two Sopwith Snipes flown by Flight Lieutenant Arthur Coningham and Flying Officer C. E.
On 31 August 1923 at the British Consulate in Constantinople, Leask married Lydia Alexandrovna, the widow of Y. Genot, and daughter of General Modestoff, of Tver, Russia.
[3] In 1924 Leask was assigned to the Air Staff in the Directorate of Operations and Intelligence,[15] and was promoted to squadron leader on 1 July 1925.
24 Squadron at RAF Kenley from 25 March[17] to 25 May 1926,[18] then attended the 21st Course at the Senior Officers' School at Sheerness until 20 August.
[21] On 1 January 1933 Leask was promoted to wing commander,[22] and then served as Senior Equipment Staff Officer at the Headquarters of RAF India from 3 February[15] until 7 September 1934.
[15] Leask was appointed a temporary air vice marshal on 1 January 1946,[31] and this promotion was made permanent on 1 October.
[34] In February 1950 Leask was appointed the manager of de Jersey & Co. (Finland) Ltd., based in Helsinki, dealing with the company's exports of engineering products from the UK.