In St. Vith, it was hard for von Manteuffel's and Dietrich's forces. The defenders resisted the German attacks. This slowed down the German advance. Montgomery ordered St. Vith to be evacuated on 21 December. U.S. troops got into trenches, which made the German advance hard. By 23 December, U.S. troops were ordered to retreat west of the Salm River. Since the German plan called for the capture of St. Vith by 18:00 on 17 December, they were behind schedule.