When the Prussian Army was mobilised for war on 9 October 1806, it was split between three major group: the Advance Guard under General Frederick Louis, Prince of Hohenlohe-Ingelfingen, the Field Army commanded by King Frederick Wilhelm III and General Charles William Ferdinand, Duke of Brunswick-Wolfenbüttel, and Generalmajor Anton Wilhelm von L'Estocq's East Prussian Corps. When mobilised, the regiment was therefore split, the regiment was assigned to the Field Army, and made part of the Karl August, Grand Duke of Saxe-Weimar-Eisenach's separate corps, based in the reserve. Sometime later the corps joined the main force and was redesignated as the Corps of Battle. Along with the Grenadier Battalion, the regiment formed part of the Field Army and was present at the disastrous Battle of Auerstadt. During the battle, the regiment along with the 30th Infantry Regiment formed part of the 1st Brigade, Infantry Division of the Advance Guard. The regiment along with the remainder of the army and grenadier battalion was decimated and fell back into Brandenburg. The regiment then, albeit significantly reduced, fought at the Battle of Weissensee, Battle of Greussen, Battle of Nordhausen, Battle of Ellingen, and finally the Battle of Ratekau where it surrendered and was subsequently disbanded. The 3rd Battalion was reformed from the depot at the same time as the mobilisation and remained in Berlin till November when joined the rest of the regiment at the Battle of Lübeck and escaped to Stettin where it also surrendered following that siege.