Cobra began the end of the Normandy campaign. When Bradley mrned his Cobra breakthrough into a breakout, rushing his forces southward, he began the second phase of the Overlord plan, introducing new forces and changing the command structure. The activation of the US 12th Army Group on August 1, gave Bradley a field command equal to Montgomerys 2lst Army Group and brought Lt. Gen. George S. Pattons Third Army into the field. Though Monty would retain temporary “coordinating authority” over both Army Groups then totaling some 38 divisions, American commanders eagerly awaited the day Eisenhowers SHAEF headquarters established itself on the continent, enabling Ike to assume control of the Allied armies.
The original forecast of operations designated Brittany and its key ports, St. Malo, Brest, and St. Nazaire plus the Quiberon Bay area, as Bradleys objective. Along with the entire area from the Brittany Peninsula to the perimeter formed by the River Loire in the south, and the Seine outside Paris in the north, this area constituted the American sector of the crucial “lodgment” required to begin the liberation of Western Europe. With 21 St Army Group taking up the area from their boundary west of the Seine outside Paris to Le Havre, the planners forecast that the entire “lodgment area” would be occupied by D + 90.
While the Allies paused to build up forces, the US 12th Army Group would switch to using Brittany’s sea ports when available, to deploy America’s armies directly from across the Atlantic. Then the 21st Army Group would take over Cherbourg for its supplies and then capture the Channel ports along the coast to mount the long drive towards Germany.
Cobras success promised a change to that concept. With the German front collapsing without an established defense in depth, the total defeat of the German armies in the west appeared possible. Attacking east, the American First, British Second, and Canadian First Armies ground up the German main defense head on, while Bradley activated Patton’s Third Army to take command of the forces breaking out of the Normandy perimeter both to seize Brittany and to position itself for its move towards the Seine.
Hitler’s defense had surprised the Allies. Their estimates indicated that the Germans would fight on successive defense lines rather than attempting to form a tight cordon close to the water’s edge. Though the defenders had held the attackers for 40 days in an area they had hoped to have captured within the first nine, fighting forward on a solid line had been cosdy. Heavy losses and the necessity to match the growing Allied force stripped the Germans of reserves, thus preventing any shift to subsequent defense lines on favorable terrain or major river lines, while off-balancing their force, leaving most German armor in the east between Bayeux and Caen. When Bradley broke out, German forces weren’t positioned to both hold the line and eliminate the breakthrough.
Breaking the ground deadlock would eventually reveal that there was a significant long term effect for the Allies in failing to gain the ground marked on 21st Army Group’s phase line map, beyond the perception of being slow or being behind schedule. The effect was a predictable shortfall in logistical support.
The Allied armies were limited in stockpiling supplies in their rear areas, which were being filled by reinforcing units. Bradley’s sudden success created a problem. As divisions quickly advanced, the long-term forward “dumping” of supplies behind the lines became impossible, with all available transportation being used to supply the rapidly-moving forces. Trucks brought food, ammunition, and most critically gasoline, directly to fighting units. Every mile forward doubled the distances for the supply vehicles. Every new division committed added hundreds of tons to the supplies.
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