When the war broke out Horace volunteered for the New Zealand Expeditionary Force. He was unable to attest until September 1915 due to operations for a hernia and appendicitis. He was otherwise fit, being described as 5ft 7inches tall, 142lb, with a dark complexion, brown eyes and brown hair. After recovering from surgery, he was commissioned, and following training he was sent to France. He was killed in action on 20 July 1916 while serving with a trench mortar battery in the New Zealand Brigade.