At the outbreak of World War I he was too old for active service, but he spent the summer of 1915 working as an orderly in the Hôpital Temporaire d'Arc-en-Barrois. The hospital had been set up in December 1914 as a temporary evacuation hospital for the French Army, and Fisher helped with X-ray work. He went on to complete his training for the Royal Field Artillery and was accepted for active service from 5 June 1917, serving in the fighting in the Ypres Salient and the Battle of Cambrai. He served as Second Lieutenant in the 36th Division (Ulster or Irish Division), but suffered appendicitis on 17 January 1918 and was invalided home. He died of peritonitis on Easter Sunday 1918 and was buried in Brockenhurst (St Nicholas) churchyard.
