Wake attended the Royal Military College, Sandhurst from 1896, and after graduating, he was appointed a second lieutenant in the King's Royal Rifle Corps (KRRC) on 17 March 1897. Wake served in South Africa during the Second Boer War from 4 November 1899. He was seconded to the staff on 13 March 1900, by which time he had been promoted to the rank of lieutenant. Wake was aide-de-camp to the Commander-in-Chief of British Forces in South Africa (initially Frederick Roberts, 1st Earl Roberts, later Herbert Kitchener, 1st Earl Kitchener) from 18 March 1900 to 1 March 1901. Wake saw action at the Battle of Colenso (15 December 1899), Battle of Spion Kop (23–24 January 1900), Battle of the Tugela Heights (14–27 February 1900) and the Relief of Ladysmith (1 March 1900). He was wounded in action during the war and was also twice mentioned in dispatches (on 3 February and 9 March 1900). Wake was awarded the Distinguished Service Order on 29 November 1900 and, during this war, also received the Royal Humane Society's bronze medal for the saving of life. Also serving on Roberts' staff in South Africa was Major Henry Wilson, with whom Wake would be associated in his later career.