After ten months in hospital, Raynal came back to the front 1 October 1915, to be again injured in the leg by shrapnel a few days later; he was then promoted to officer of the Legion d'Honneur.

Not being able to walk properly seemed to end his military career; however, later in 1916, the Ministry of War in France decided that officers who could not serve on the front line could instead take command of fortresses and other fortifications.

He led a stout defense of Vaux over six days of brutal combat, with his eventual surrender forced by his men literally dying of thirst.

The defense was so heroic that the commander of the German army opposing him, Crown Prince Wilhelm, honored him with a sword to replace the one lost during the battle.

Major Raynal was also filled with strong civic engagement: before the war, he had supported the action of Jaurès and Socialist Party.