Harry enlisted into the 1st Home Counties Divisional Field Ambulance, R.A.M.C., T.F. on 30th April 1912. He was 17 years and 6 months old; was a Boy by trade at H.M. Dockyard, Chatham; and was living at 102 King Street, Rochester at the time. He became one of a quota of N.C.O.’s and men, known as 'Special Reserve', who previously agreed to serve overseas in the event of a war. On 6th August 1914, he transferred from the 1st Home Counties Field Ambulance to serve with the Expeditionary Force, and marched alongside Captain Greene, and the detachment, to a field adjoining Monockton’s Mill, Sandling Road, Maidstone, which had become the mobilization headquarters of No 10 Field Ambulance. He entered the war with the 10th Field Ambulance on 23rd August 1914, and served with the unit until 21st August 1915, when he was sent back to England, but he returned to France on 14th October 1915. On 21st January 1916 he was sent to Base Details at Rouen, who transferred him to England. On 29th January 1916 he was posted to the 9th Provisional Field Ambulance, Margate, to determine whether he should continue with the regular army or be transferred back to the Territorial Force. He was reverted back to his Territorial Force unit. On 20th May 1916 he was posted to the 4/1st Home Counties Field Ambulance, and served with them until 27th August when was transferred to the 2/1st Home Counties Field Ambulance. He went with the unit to Southampton on 23rd January 1917, and re-entered the war in France the following day. He served the remainder of the war with this unit, being disembodied on 9th April 1919, then discharged on demobilization from the Army on 31st March 1920.