Lauer fought on the upper Rhine River under the command of Dagobert Sigmund von Wurmser in 1793–1794. On 13 October 1793, Wurmser defeated the French in the First Battle of Wissembourg and the next day Lauer employed his expertise to besiege Fort-Louis. A strong position situated on an island in the Rhine River and held by a garrison of 4,500, on 14 November he accepted its surrender. Still with Wurmser, he fought at the successful Siege of Mannheim in late 1795. For notable actions in capturing the Neckerauer redoubt on 30 October, he earned the Commander's Cross of the Military Order of Maria Theresa. Promotion to Feldmarschall-Leutnant followed on 4 March 1796.