Complex sentence: He was part of the army of the Vosges and commanded the fort Vauban on 11 August 1792, when the November 8 after he was appointed lieutenant colonel and engineer-in-chief of the army.
Split into simpler sentences: He was part of the Army of the Vosges and commanded the Vauban fortress on 11 August 1792. Subsequently, he was appointed lieutenant colonel and engineer-in-chief of the army.