Complex sentence: Upon his return, on 17 September 1940 he was assigned to the Office of the Secretary of State for War in Vichy, under General Charles Huntziger the Secretary of State for War until he died in a plane crash on 12 November 1941.
Split into simpler sentences: Upon his return, on 17 September 1940 he was assigned to the Office of the Secretary of State for War in Vichy. There he was under General Charles Huntziger the Secretary of State for War until he died in a plane crash on 12 November 1941.