In April 1915 Hone passed the British civil service examination. He then joined the Inns of Court Regiment and was commissioned in July 1915 in the London Irish Rifles. He was posted to the 1/18th battalion and was involved in the Battle of Loos in autumn 1915. Hone served in the Notre Dame de Lorette sector and then at Vimy Ridge. During this time Hone was hospitalised with acute trench fever and impetigo. He was promoted to lieutenant on 14 April 1917, and to acting captain on 14 January 1918.