As the French advanced into Poland, they clashed with the Russians and Prussians in a series of actions, the most prominent of which was the Battle of Czarnowo on 23 and 24 December 1806. On the 24th, Ney sent Marchand's division ahead to seize Działdowo (Soldau) and Mława. He arrived at Soldau at 2:00 PM on 25 December with two regiments and expelled the lone Prussian battalion he found there. Shortly afterward, his remaining two regiments joined him after marching via Mława. At 5:00 PM, Christoph Friedrich Otto Diercke's Prussian brigade turned up and attacked Soldau but was repulsed after stiff fighting. Marchand reported losing 220 casualties out of 6,000 troops and 12 guns, while Ney claimed his lieutenant inflicted 800 casualties on Diercke's 3,000 men and 8 guns. At this time, the 6th Light had temporarily been replaced by the 27th Line Infantry Regiment, while the other units remained the same. Marchand led his division at the Battle of Eylau on 8 February 1807.