 "Mestre de camp" of the régiment du Roi-Cavalerie from 26 March 1744, he was maréchal de camp and commandant général of the cavalry from 1748.In 1756, he commanded the expeditionary force sent to St Lucia, and the Carenage quarter of the island was renamed Castries after him.He next distinguished himself in the Battle of Rossbach (5 November 1757), in which he was wounded twice.