Ernest enlisted with the Dorsetshire Regiment as a Private (Service No. 6151). He served in France and Flanders with the 8th Battalion and was taken prisoner at La Bassee, France, on 23rd January 1915 and sent to Prisoner of War camp at Mersebury, near Liepzig in Germany. This was Camp Altengrabow. While there he had a trinket box and a cup made for his wife Laura Mary and engraved with her initials. Following his release he was not discharged until 31st March 1920. He was awarded the Victory and British War medals as well as the 1914 Star.
His death was recorded in Edenbridge, Mere, Wiltshire, on 6th April 1935 and he was buried at Mere on 10th April 1935. One of his brothers, Thomas William Gatehouse, also served in the conflict and his nephew, Victor Stokes, was killed during the war in an accident.