After possibly six months as a captain in the regiment guard in 1708, on 11 February 1709 he joined the Regiment on foot in Anhalt-Zerbst (No. 8) which later changed its name to the Grenadier's Regiment King Frederick William IV of Prussia. It was stationed in Stettin. In 1711, Christian August was awarded the Order "De la Générosité", later renamed in "Pour le Mérite", and on 1 March 1713 was elevated to the rank of lieutenant-colonel. After he took part in several military campaigns during the Spanish War of Succession and in the Netherlands, in 1714 Christian August was appointed Chief of the Regiment; two years later, on 4 January 1716 he was named colonel and on 14 August 1721 became major-general.