From 1799 Yorck began to make a name for himself as commander of a light infantry ("Jäger") regiment, being one of the first to give prominence to the training of skirmishers. In 1805, then with the rank of "Oberst", he was appointed to the command of an infantry brigade as a vanguard force of the troops of Duke Karl August of Saxe-Weimar during the War of the Fourth Coalition. In the disastrous Jena campaign he played a conspicuous and successful part as a rearguard commander, especially at Altenzaun. Having made his way across the Elbe river and through the Harz mountains, he was taken prisoner, severely wounded, in the last stand of Blücher's corps at Lübeck.