After securing territory in the Cotentin Peninsula south as far as Saint-Lô, the U.S. First Army launched Operation Cobra on 25 July and advanced further south to Avranches by 1 August. The British launched Operation Bluecoat on 30 July to secure Vire and the high ground of Mont Pinçon. Lieutenant General George S. Patton's U.S. Third Army, activated on 1 August, quickly took most of Brittany and territory as far south as the Loire, while the First Army maintained pressure eastward toward Le Mans to protect their flank. By 3 August, Patton and the Third Army were able to leave a small force in Brittany and drive eastward towards the main concentration of German forces south of Caen. Over Kluge's objections, on 4 August Hitler ordered a counter-offensive (Operation Lüttich) from Vire towards Avranches.
While II Canadian Corps pushed south from Caen toward Falaise in Operation Totalize on 8 August, Bradley and Montgomery realised that there was an opportunity for the bulk of the German forces to be trapped at Falaise. The Third Army continued the encirclement from the south, reaching Alençon on 11 August. Although Hitler continued to insist until 14 August that his forces should counter-attack, Kluge and his officers began planning a retreat eastward. The German forces were severely hampered by Hitler's insistence on making all major decisions himself, which left his forces without orders for periods as long as 24 hours while information was sent back and forth to the Führer's residence at Obersalzberg in Bavaria. On the evening of 12 August, Patton asked Bradley if his forces should continue northward to close
the gap and encircle the German forces. Bradley refused, because Montgomery had already assigned the First Canadian Army to take the territory from the north. The Canadians met heavy resistance and captured Falaise on 16 August. The gap was closed on 21 August, trapping 50,000 German troops but more than a third of the German 7th Army and the remnants of nine of the eleven Panzer divisions had escaped to the east.
Montgomery's decision-making regarding the Falaise Gap was criticised at the time by American commanders, especially Patton, although Bradley was more sympathetic and believed Patton would not have been able to close the gap.
"Although Patton might have spun a line across the narrow neck, I doubted his ability to hold it. Nineteen German divisions were now stampeding to escape the trap. Meanwhile, with four divisions George was already blocking three principal escape routes through Alencon, Sees and Argentan. Had he stretched that line to include Falaise, he would have extended his roadblock a distance of 40 miles (64 km). The enemy could not only have broken through, but he might have trampled Patton's position in the onrush. I much preferred a solid shoulder at Argentan to the possibility of a broken neck at Falaise."
"The battlefield at Falaise was unquestionably one of the greatest "killing fields" of any of the war areas. Forty-eight hours after the closing of the gap I was conducted through it on foot, to encounter scenes that could be described only by Dante. It was literally possible to walk for hundreds of yards at a time, stepping on nothing but dead and decaying flesh."
Hitler relieved Kluge of his command of OB West on 15 August and replaced him with Field Marshal Walter Model. Kluge committed suicide on 19 August after Hitler became aware of his involvement in the 20 July plot.
A few days later, the Allied Liberation of Paris was completed, and on 30 August the remnants of Army Group B retreated across the Seine, which ended Operation Overlord.