A large number of American troops flooded into Britain as part of Operation Bolero. The initial invasion plans drafted during the 1943 Operation Round-up were criticised as too narrow by the newly appointed Supreme Allied Commander Europe, General Eisenhower and the British land force commander, General Montgomery. As a result the invasion plan was changed to an assault over five beaches rather than three, plus the use of three airborne divisions. The date for Operation Overlord was set for 5 June but a sudden deterioration in weather prompted a 24-hour delay, and D-Day was re-planned to take place on 6 June 1944.
Across a 60-mile front, Allied seaborne and airborne forces assaulted German defences. The most easterly British beach was Sword, then, moving west, was Juno followed by Gold. Then came the easternmost American Beach, Omaha, and separated by the River Vivre estuary was the other American beach - Utah. In the east of the assault area, during the early hours of 6 June, the British 6th Airborne Division seized bridges across the Orne River and Cean Canal at Ranville as well as destroying bridges further east over the Dives River in order to protect the flank of the invading forces. British and Commonwealth forces landed across 24 miles of beaches. In the east, the British and Canadian forces, made up of the British 50th Infantry Division, Canadian 3rd Infantry Division and British 3rd Infantry Division, moved inland from Gold, Juno and Sword beaches. Although not quite achieving their D-Day objective, they secured a large and viable lodgement area.
At Utah, in the far west of the invasion area (despite the dispersal of the American 82nd and 101st Airborne divisions due to poor aircraft navigation and enemy anti-aircraft fire) the lead seaborne assault division, made up of the US 4th Infantry Division, came ashore without serious opposition and moved inland. However, at Omaha the US 1st Infantry and US 29th Infantry Divisions faced hard and very costly fighting and at the end of D-Day the American hold on the beach area was far from secure.
Over the next few weeks the lodgement area slowly expanded in the face of very stiff German resistance. An operation by the British 2nd Army ensured that the bulk of the German Panzer divisions were facing the British in the area of Cean. This allowed the American 1st Army to launch an attack on 25 July from the area of St Lo, breaching German defences in the area. American divisions raced through the gap, some moving west into Brittany, but most advancing east towards the River Seine. The bulk of German forces were defeated between 8 and 18 August in the area of Falaise. The elements of German divisions that had escaped destruction retreated rapidly towards Germany, pursued by Allied forces.
On 25 August the British 2nd Army crossed the River Seine and Brussels was liberated on 3 September. On 15 August another invasion of France took place in the south - Operation Dragoon. The American 7th Army moved swiftly up from Marseilles and Toulon to join the American 1st and 3rd Armies, the British 2nd Army, and the Canadian 1st Army that had broken out of Normandy.
In early September as Allied forces reached the Dutch and German border areas, their logistic support ran out. The Germans recovered rapidly and formed a front line where they could make use of the Westwall fortifications.