[1] He was a school prefect and head of house at Malvern, played in the football team and was in the Officers' Training Corps.
He passed the Army Entrance Exam in 1916 and graduated from Sandhurst after a six-month, war-shortened course later the same year.
[2] After graduating from Sandhurst, Capes was commissioned as a 2nd Lieutenant in the Royal West Kent Regiment (RWK) in October 1916.
He saw action at the Battle of Sharqat in October 1918 immediately before the Armistice of Mudros brought the war with Turkey to an end.
[2] Capes returned to England in April 1919 and was demobilised, resigning his commission in November the same year.