Percy enlisted on 18th December 1911. He was 17 years and 11 months old at the time. He entered the war in France on 17th August 1914, as part of the Regimental Medical Officer's team for the 26th Brigade. Royal Field Artillery. On 27th September 1915 he was wounded in action, suffering from the effects of gas, and was evacuated back to the UK on the hospital ship 'St George', via No 10 General Hospital on 5th October 1915. On 4th February 1916 he embarked at Southampton with No 32 General Hospital, disembarking in Basra on 10th April. On 18th August 1917 he was admitted into hospital - "not yet diagnosed", then was invalided to India on 10th September. He was admitted into No 34 (Welsh) General Hospital on the 18th September, then was transferred to No 44 General Hospital on 3rd November. He remained there until 8th February 1918 when he was sent to the Convalescent Section. He joined the R.A.M.C. Depot on 15th February who posted him for embarkation to East Africa. He served in East Africa until 16th February 1919, when he was transferred to Home Establishment and embarked on H.T. 'Voronej' at Daressalaam. Once back in the UK he was stationed in Blackpool until he was transferred to Class 'Z' on demobilization on 30th April 1919.