After their defeat in Normandy from June to August 1944, remnants of German forces withdrew across the Low Countries and eastern France towards the German border. In the north, in the first week of September, the Anglo-Canadian 21st Army Group (Field Marshal Bernard Montgomery) was advancing on a line running from Antwerp to the northern border of Belgium with its British Second Army (Lieutenant-General Sir Miles Dempsey) while the First Canadian Army (Lieutenant-General Harry Crerar) had commenced its task of recapturing the ports of Dieppe, Le Havre and Boulogne-sur-Mer. To the south, the US 12th Army Group (Lieutenant General Omar Bradley) was nearing the German border and had been ordered to advance on the Aachen gap with the US First Army (Lieutenant General Courtney Hodges) in support of Montgomery's advance on the Ruhr, while its US Third Army (Lieutenant General George S. Patton) moved eastward towards the Saar. The US 6th Army Group (General Jacob L. Devers) was advancing towards Germany after Operation Dragoon, the invasion of southern France. Montgomery devised an ambitious plan called Operation Market Garden which would take place in mid-September; it was intended to bypass the Siegfried Line by hooking around its northern end and thereby allow the Allies to cross the Rhine in force and trap the German 15th Army between Arnhem and the shores of the IJsselmeer. Market, the airborne element of the plan, would employ four of the six divisions of the First Allied Airborne Army. The US 101st Airborne Division (Major General Maxwell D. Taylor) would drop in two locations just north of XXX Corps to take the bridges north-west of Eindhoven at Son and Veghel. The 82nd Airborne Division (Brigadier General James M. Gavin) would drop north-east of them to take the bridges at Grave and Nijmegen and the British 1st Airborne Division (Major-General Roy Urquhart) and the Polish 1st Independent Parachute Brigade would drop at the extreme north end of the route, to take the road bridge at Arnhem and the rail bridge at Oosterbeek.