Percy enlisted into the R.A.M.C. Territorial Force on 9th August 1915, and was embodied into the 1/1st Wessex Casualty Clearing Station. He was 20 years and 11 months old, and was living at 65 Windsor Road, Ellacombe, Torquay at the time. On 18th September 1915 he was appointed temporary Corporal. He embarked at Southampton on 27th May 1916, then disembarking at Havre, he entered the war in France on 28th May 1916. On 18th September 1915 he was promoted to the rank of Corporal, then on 17th January 1916 was appointed temporary Lance Serjeant, and on 26th July 1917 was appointed acting Serjeant. On 12th March 1918 he joined the 141st Field Ambulance for duty. His rank reverted back to Corporal on 12th August 1918. On 2nd December 1918 he was evacuated 'sick' to a Casualty Clearing Station. He then rejoined the unit from R.A.M.C. Base Depot on 13th January 1919. On 2nd July 1919 he proceeded to No 1 Concentration Camp, Cologne for dispersal and was struck off the strength of the unit. He was disembodied on demobilization on 5th August 1919.