Benoit joined up at the beginning of the Great War, telling his mother enthusiastically in a letter that he was about to join a “holy war”. He was involved in the Battle of Charleroi, one of the first battles between French and German forces, between 21 and 23 August 1914. After this, he fell gravely ill, and spent several months in hospital before being invalided out of the army. He became a convinced pacifist.
The above information comes from Wikipédia.