While Allied troops made slow progress in Normandy through most of June and July, the US 12th Army Group under General Omar Bradley started to make rapid progress at the beginning of August, thanks to the success of Operation Cobra. By August 4 the German front facing the 12th Army Group had largely collapsed. A small but fierce German counter-offensive (Operation Lüttich) was launched on August 7 at Mortain. This was a last-ditch attempt at halting the Allied breakthrough by cutting off General George Patton's Third Army.
The Germans' Mortain counterattack was an unwise move because it shifted the weight of their forces westward at the very time when they needed to retreat eastward. In the process the Germans had been weakened, and Allied commanders Bradley and Bernard Montgomery moved to exploit the situation with a plan to encircle the Germans.
Under the combined pressure of the Americans and French to the south, the British to the west, and the Canadians and Poles to the north, by August 10 the Germans were aware of the danger of encirclement, although Hitler was demanding another counter-attack on Avranches rather than a deliberate withdrawal.
Cool I mentioned this on one of the boards.
Yeah, I have been toying with the idea since the Arnhem game last year, I put it to the CiA Brass, and they suggested I give it some thought, get a venue sorted and it organised... so here we are 
