Tactical command for cobra fell to aggressive VII Corps commander Major General J. Lawton Collins. Collins would have six divisions and almost 100,000 men for the attack. The plan hinged on a concentrated strike by heavy bombers to destroy a significant portion of the German lines. After the bombardment, an overwhelming ground attack by the U.S. 9th, 4th, and 30th Infantry Divisions would penetrate the disrupted German defenses and hold open a corridor for the exploiting mobile divisions. Opposing Collins was the German LXXXIV Corps, which had experienced heavy fighting and had many understrength units, such as the Panzer Lehr Division, which could muster only 3,200 troops along a 3-mile front.
A key element in the cobra plan was to locate a point of penetration where there were sufficient parallel roads in the direction of the attack to allow follow-on forces into the breach. The most controversial aspect of the operation was the "carpet bombing" by strategic bombers. Bradley designated a rectangular target box 2,500 yards wide and over 7,000 yards long, and his IX Tactical Air commander, Major General Elwood "Pete" Quesada, met with Air Chief Marshal Sir Trafford Leigh-Mallory to coordinate the air attack. However, the competing needs for dropping maximum bomb tonnage, maintaining tactical positions for the infantry, and placing 1,500 bombers in the milewide corridor in a single hour could not be entirely reconciled.
cobra was scheduled for 24 July, but overcast skies led Leigh-Mallory to call off the carpet bombing. Unfortunately, Eighth Air Force bombers were already in flight, and they approached the target from a perpendicular direction, causing bombs to fall short of the target and into the 30th Infantry Division, killing 25 and wounding 131. The attack postponed and the surprise lost, an infuriated Bradley was told that another attack would follow the next day.
On 25 July, bombers dropped 4,400 tons of bombs. The Germans, alerted from the previous attack, had dug in. Despite this, the Panzer Lehr Division was left in shambles, with 70 percent of its soldiers suffering shock and several battalion command posts destroyed. The Americans, in exposed positions and ready to move, suffered in "shorts" (bombs that fell short of their targets, landing on friendly forces) another 111 men killed, almost 500 wounded, and psychological trauma for 200 more. Among the U.S. dead was Lieutenant General Lesley J. McNair, commander of Army Ground Forces, who was visiting the front to observe the attack.
In spite of this tragedy, VII Corps immediately attacked, although strong pockets of German resistance limited the advance to only a mile or two. The next day, Collins made a bold decision to commit his armored and motorized forces, even though no U.S. unit had reached its planned objectives. The disrupted German command-and-control network failed to react when U.S. armored divisions sliced through the lines on 26 July. The next day, Collins's mobile units exploited their success deeper into the German rear areas, which led Bradley to order VIII Corps through the breach to seize Avranches.
According to the plan, once forces moved toward Brittany, the Third U.S. Army, commanded by Lieutenant General George S. Patton Jr., would be activated. To facilitate this transition, Bradley gave Patton immediate command of the VIII Corps, which he drove hard to capture Avranches on 31 July and mark the end of cobra. In just six days, the entire German Front collapsed, enabling the Allies to carry out their own operational blitzkrieg deep into France.
Steven J. Rauch
Blumenson, Martin. Breakout and Pursuit. Washington, DC: Center of Military History, 1961.; Carafano, James J. After D-Day: Operation Cobra and the Normandy Breakout. Boulder, CO: Lynne Rienner, 2000.