Moutoux would take part in the Meuse-Argonne Offensive. In Liny-Devant-Dun, France, the 5th Infantry Division successfully pushed back the German Army on November 5, 1918. In the early morning of November 6, 1918, Moutoux walked into a barn with Chaplain 1st Lieutenant John Dick Van Horn. The Germans had artillery on the hill north of Liny where they fired down on the village. Three shells struck the barn. The very last one spit out a shrapnel piece into the middle part of Moutoux's back. He was killed instantly.

To Moutoux's brother, Ernest, - Chaplain's Office, 11th Infantry, Jan 8, 1919. "My Dear Sir: Corporal Karl Moutoux happened to be in the same building with me on Nov 6, 1918, at Liny, across the Meuse river. We were right behind our front line and stepped into a barn. Three shells struck it directly. the last one killed your brother by a piece of shrapnel in the middle of the back. He was lying against me at the time and I didn't realize he was killed for he did not change position and I imagined he was awaiting another shell. I buried him with three other companions near the building in which he met his death. My assistant was severely wounded and I was slightly wounded. The few personal belongings were sent. I hope they reached you. Sincerely yours, J. D. Van Horn. Chaplain 11th Infantry."