Prince Karl joined the Bavarian Army and rose to be Field Marshal in 1841. At the age of 71, he commanded the Bavarian forces in the Austro-Prussian War with General Ludwig von der Tann. It was not a success, as troops under their command often found themselves in the wrong location, or were slaughtered by the Prussians. In one incident, the German Confederation Union Army 7th Corps received orders to join up with the retreating Hanoverian army at Hersfeld. Prince Karl did not know his allies' location and simply waited, until it was too late.