Following the outbreak of war, Young was found medically unfit for overseas service and had to undergo an operation. In January 1915 he was passed fit and was posted with a reinforcement draft to 1/1st battalion Hertfordshire Regiment, then serving as part of the British Expeditionary Force on the Western Front. His father had rejoined the army and was serving as the battalion's Regimental Sergeant Major. Both father and son saw service through successive engagements in 1915, including the Battles of Festubert and Loos and during this period the latter was promoted to Sergeant. In 1916 he was appointed as a bombing instructor at the Rouen Central Bombing School, but was wounded in an accident. After a period of recovery Young was selected for officer training and was subsequently commissioned as a Second Lieutenant on 27 April 1917, being posted to a reserve battalion of the Bedfordshire Regiment in Britain. Following an interlude training with the Royal Flying Corps, Young returned to the infantry and was sent to rejoin the 1/1st Hertfordshires in France on 12 September 1918, being appointed commander of No. 4 Company on arrival.