Montgomery's 21st Army Group advanced to the Rhine with operations Veritable and Grenade in February 1945. A carefully-planned Rhine crossing occurred on 24 March. While successful it was weeks after the Americans had unexpectedly captured the Ludendorff Bridge at Remagen and crossed the river. Montgomery's river crossing was followed by the encirclement of the German Army Group B in the Ruhr. Initially Montgomery's role was to guard the flank of the American advance. This was altered, however, to forestall any chance of a Red Army advance into Denmark, and the 21st Army Group occupied Hamburg and Rostock and sealed off the Danish peninsula.