Following the German counter-attack at Mortain on 6 August 1944, Generals Omar Bradley and Bernard Montgomery decided to engage in a wide encircling movement, to trap the enemy divisions which had advanced so far westwards. American XV Corps entered Le Mans on 9 August and then advanced rapidly northwards, capturing Alencon before moving towards Ecouche, then Argentan. Meanwhile, Montgomery had broken the German front south of Caen despite stiff resistance. The Canadians and the Poles of General Maczeck's 1st Armoured Division bore down on Falaise, eventually capturing the town on 16 August.

They then accelerated their advance, seeking to meet American forces moving northwards. With over 100,000 Germans in danger of encirclement, Hitler gave the order for a general withdrawal. Under the combined pressure of the Americans and French to the south, the Americans and British to the west and the Canadians and Poles to the north, the net inexorably tightened. American and Polish units linked up at Chambois as Canadian and Polish forces attempted to plug the remaining gaps in a series of ferocious actions. With Allied artillery and air power taking a heavy toll, the Germans' retreat gradu