He served as a captain of guides on the Prussian General Staff during the French campaign and helped take the fortresses at Longwy and Verdun. He then caught dysentery and stayed in a hospital in Koblenz until November 1792. The king made Rauch a lieutenant colonel in 1796 and put him in charge of the Engineering Academy. He became a major general in 1805 and was made deputy governor of Stettin on the outbreak of the War of the Fourth Coalition in summer 1806, with the 77-year-old lieutenant general von Romberg as governor. After the defeats in the battle of Jena-Auerstedt, Prussia's field army retreat and began to split up. Romberg's morale collapsed and when eight hundred French cavalry arrived before Stettin on 29 October 1806 he surrendered immediately without waiting to assess the size of the enemy force, which was vastly dwarfed by Stettin's garrison of 5,184.