Troughton was commissioned, initially as a second lieutenant, in the Rifle Brigade during the First World War. He served with the 10th Battalion on the Western Front from 1915, rising to command the battalion with the rank of lieutenant colonel. In September 1916, whilst a company commander, he was awarded the Military Cross for leading his men in an attack at Guillemont with "conspicuous gallantry", as well as a Légion d'honneur, Croix d'Officiers, the first to be awarded in XIV Corps. He was captured and made a prisoner of war during a German attack at Cambrai in 1917, and was decommissioned at the end of the war.