[2] As with so many other young men of his generation, he served in the First World War, being awarded the Distinguished Service Order and Military Cross.

[6] On 1 October 1935 Wemyss was promoted colonel[7] and appointed an Assistant Adjutant General at the War Office in London.

On completing the course, he was promoted to major general[8] and appointed as the Director of Mobilisation at the War Office on 9 January 1939.

[6] On 10 June 1940, nine months after the outbreak of the Second World War, Wemyss replaced General Robert Gordon-Finlayson as Adjutant-General to the Forces.

He was promoted general on 15 October 1945, by which time the war was over, and retired from the army, after having served for almost exactly thirty-six years of service, on 23 November 1946.