On 9 February , the U.S. Ninth Army—operating under Field Marshal Sir Bernard Montgomery 's Anglo-Canadian 21st Army Group since the Battle of the Bulge—was to cross Motion_directional the Roer and link Connect up with the Canadian First Army , under Lieutenant-General Harry Crerar , coming from the Nijmegen area of the Netherlands in Operation Veritable , which had started Process_start at 05:00 on 8 February .