On 25 July 1944, following six weeks of attritional warfare along a stalemated front, American forces under Lieutenant General Omar Bradley mounted an attack code-named Operation Cobra, which broke through the German defenses near Saint-Lô.

[4] Despite German air attacks against the bridge at Pontaubault, Patton pushed no less than seven divisions across it during the next three days, and units of his army began advancing almost unopposed towards the Brittany ports.

Although the Germans held the vital road junction of Vire, U.S. VII Corps, under Major General J. Lawton Collins, captured Mortain, 19 miles (31 km) east of Avranches, on 3 August.

[6] Major General Wade H. Haislip's U.S. XV Corps advanced no less than 75 mi (121 km) during the next three days, and by 7 August they were approaching Le Mans, formerly the location of the headquarters of the German 7th Army, and still an important logistic center.

After Generalfeldmarschall Erwin Rommel was injured by Allied aircraft on 17 July, Kluge also took over direct command of Army Group B, the formation conducting the battle in Normandy.

On 2 August, Hitler, fearing the loss of U-boat pens on the French coast, sent a directive to Kluge ordering "an immediate counter-attack between Mortain and Avranches".

[7] General Walter Warlimont—the Deputy Chief of Staff at OKW, the German armed forces headquarters—was also sent to Kluge's headquarters to ensure these orders were complied with.

[6] Kluge suggested that there was no chance of success, and the German forces in Normandy should retire to the Seine River, pivoting on the intact defences south of Caen, but on 4 August, Hitler categorically ordered the attack to be launched.

[9] Although ordered to wait "until every tank, gun and plane was assembled", Kluge and SS General Paul Hausser (commanding the German 7th Army, which held the western part of the front) decided to attack as soon as possible, before the overall situation deteriorated further.

[11] The intention was to hit the U.S. 30th Infantry Division, commanded by Major-General Leland Hobbs, east of Mortain,[11] then cut through American defenses to reach the coast.

[11] Despite assurances by the Luftwaffe that German forces would have adequate air support,[13] the Allied aircraft quickly achieved complete control of the airspace over Mortain.

[18] In the open ground east of Mortain, the German Panzers became exposed targets, especially for rocket-firing Hawker Typhoon fighter bombers of the RAF.

[20][page needed][3] General Speidel, Chief of Staff to Field-Marshal Von Kluge, wrote after the war "The armoured operation was completely wrecked exclusively by the Allied Air Forces supported by a highly trained ground wireless organization".

[21] Author and Typhoon pilot, Desmond Scott states that the battle of Mortain "proved conclusively that major ground offensives can be defeated by the use of tactical air power alone".

[23] In one British study, it was found that the average Typhoon pilot firing a barrage of all eight rockets had only a four percent chance of striking a target the size of a tank.

In the afternoon, the 1st SS and 116th Panzer Divisions made renewed attacks, but the flanks of the Mortain positions had been sealed off, allowing the American VII Corps to contain the German advance.

[29][30][1] As Hitler ordered German forces in Normandy to hold their positions,[28] the U.S. VII and XV Corps were swinging east and north toward Argentan.