Zach was promoted to Feldmarschallleutnant on 1 September 1805. That year he served as chief of staff in Archduke Charles' "Armee von Italien". The army fought the Battle of Caldiero from 29 to 31 October. This action was Austria's best showing during the War of the Third Coalition. After the war, Charles dismissed Zach as too old to serve as chief of staff. On 23 September 1807, Zach became Proprietor (Inhaber) of Infantry Regiment Nr. 15 and held the post during his lifetime.