In 1783, Gustavus III asked von Fersen to join him in Germany as Captain of the Guard. Gustavus was planning on making war on Denmark, and was on a trip through the Continent to secure aid from other countries. Gustavus promoted von Fersen to titulary-colonel in the Swedish army, chevalier of the Order of the Sword, and lieutenant-colonel of the light-horse cavalry of the king. Gustavus also used his influence to persuade Louis to have von Fersen appointed proprietary colonel of the Royal Suédois French Army infantry regiment. Louis also appointed von Fersen second-colonel of the Royal Deux-Ponts regiment and chevalier of the Order of Military Merit.