The combat of Czarnowo (23 December 1806) saw the French establish a bridgehead on the east bank of the River Ukra, at the point where it flows into the River Bug (War of the Fourth Coalition).
By mid-December 1806 the French had occupied Warsaw, crossed the Vistula and had established a foothold on the north bank of the River Bug, just above its junction with the Vistula (north of Warsaw). The Russians were holding the line of the River Ukra, which flows into the Bug just upstream of the French bridgehead, although Davout had already occupied an island in the mouth of the Ukra.
The area between the Bug and the Ukra was low lying, swampy and partly wooded. It was bounded by a bank of higher ground which ran from the village of Czarnowo on the north bank of the Bug west towards the Ukra, reaching it nearly two miles to the north of the Bug, opposite the village of Pomiechowo. This position was defended by Osterman Tolstoi's division, with nine infantry battalions, two cavalry squadrons, one Cossack regiment and twenty guns.
Davout had three divisions in the area. Morand was already on the island in the Ukra. Friant's division was close to Pomiechowo. Gudin's division was at the French bridge over the Bug.
Napoleon decided to cross the river after dark on 23 December. He produced very detailed orders for the river crossing. Morand formed three columns, each one battalion strong. Each had a company of voltigeurs at its head. These troops covered the French guns, which open fired across the river. The voltigeurs then crossed the Ukra in boats and established a foothold on the east bank. Three bridges were built connecting these footholds to the island - one at its northern tip, one in the centre and one at the southern end. The three battalions then crossed the river, followed by the 17th light infantry and then by three squadrons of cavalry. The rest of Morand's division followed on behind.
On the French left Petit led part of Gudin's division across the northern bridge and advanced up the river towards the Russian right. His attack was supported by six guns firing across the river from Pomiechowo and by a small detachment of marksmen who advanced up the west bank of the river.
The Russians were quickly pushed off the low ground, but they put up more resistance at Czarnowo. The first French attack, by the 17th light, was repulsed after briefly gaining access to the village. A second attack, by the 30th Line, was also fiercely resisted, but eventually French weight of numbers forced the Russians to abandon the village. Morand was able to take up a position on the bank, which marked the edge of a plateau of higher and thus drier ground. On the French left Petit's detachment captured a number of Russian artillery redoubts near the Ukra, but the guns had already been withdrawn. The Russians launched a cavalry counterattack, but this was fought off. The Russians then made a series of infantry attacks on the redoubts, but there were also fought off.
At 4am on the morning of 24 December, nine hours after the French attack began, Osterman Tolstoi decided to retreat. He had just received reinforcements and was able to pull back towards Nasielsk, seven and a half miles to the north of Czarnowo without any problems. The French had thus established a bridgehead on the east bank of the Ukra.
Casualty figures on both sides are rather uncertain. The Russians lost somewhere between 500 and 1,392 killed and wounded. Davout reported 807 casualties, although this probably didn't include Petit's detachment.