In 1853 he was entrusted with the duties of the brigade major and with the management of the Oldenburg military school. In 1855 Weltzien was promoted to company commander and chamberlain. After his promotion to major, he was assigned to the Military Commission of the German Confederation in Frankfurt am Main for two years on February 1, 1859. In this capacity, promoted to lieutenant colonel in mid-March 1860, Weltzien was used as battalion commander after his return to service. On January 1, 1862, he was promoted to colonel and regimental commander. Major general since April 30, 1865, Weltzien was the successor of Wilhelm von Ranzow who was the commander of the Oldenburg troop corps and commander of the Oldenburg-Hanseatic brigade. In the next year, he led this brigade in the Austro-Prussian War as part of the Prussian Main Army against Austria's southern German allies and fought against the Baden Division in the Battle of Werbach. For his achievements Weltzien received the Honorary Commander's Cross of the House and Merit Order of Peter Frederick Louis with the Swords and the Order of the Red Eagle from the Prussian King Wilhelm I, 2nd Class with oak leaves and swords.