After the outbreak of the First World War, Le Fleming resigned his position at Sandhurst to rejoin his regiment in October 1914, serving with 1 battalion in northern France. He fought at the Battle of La Bassée and was wounded in the face at Richebourg-l'Avoué near Bethune towards the end of October. The wound was severe enough for him to be invalided home for treatment and it was during his recovery period that Le Fleming married.