In the 1812 invasion of Russia, Doumerc led the 3rd Heavy Cavalry Division, a part of the III Cavalry Corps under Emmanuel Grouchy. Detached from its parent corps, the 3rd division fought at the First Battle of Polotsk on 16 to 18 August 1812. On the first day, Marshal Nicolas Oudinot suffered a tactical defeat and was wounded. Laurent Gouvion Saint-Cyr took over and on the 17th, he maneuvered as if preparing to retreat. The next day, he hurled the VI Corps, consisting of Bavarians, at the Russian left flank. The French II Corps attacked the Russian center while the French cavalry opposed the Russian right. Staring at defeat, the Russian commander Peter Wittgenstein threw in his last reserves, headed by depot squadrons of the Lifeguard Uhlans, Hussars, and Dragoons. The Russian horsemen achieved initial success. But they were checked by a Swiss regiment and broken by a charge of the 4th Cuirassier Regiment led by Frédéric de Berckheim, one of Doumerc's brigadiers.