Lewis joined the Royal Flying Corps in 1915, after lying about his age and learned to fly at Brooklands. In 1916, he flew the Morane Parasol on operations with No. 3 Squadron and was awarded the Military Cross for his actions during the Battle of the Somme. Flying over the battlefield on the First day on the Somme (1 July 1916) to report on British troop movements, Lewis witnessed the blowing of the mines at La Boiselle. He later described the early morning scene in his book "Sagittarius Rising"