D-Day, the start of the Allied invasion of Europe, began early on 6th June when 23,000 British and American airborne troops landed in Normandy inanticipation of a five-division beach assault by over 130,000 British, American and Canadian troops a few hours later. Though there ware serious difficulties with one of the American landings, by nightfall the German beach defenses had been overcome with much lighter Allied casualties than anticipated.
Now that the Allies were successfully established ashore and building up their forces, a counterattack by Army Group B was inevitable. The German response, however, was slowed by overly complex command arrangements (Rommel, von Rundstedt and Hitler all having a hand in the deployment of armoured forces), an ongoing belief that the main attack was still to come in the Pas-de-Calais, and the manner in which the French Resistance and Allied bombing hindered the movement of armoured reserves to Normandy. This allowed the Allies time to consolidate their hold and push inland twenty miles or so in the face of only uncoordinated and sporadic counterattacks over the next few weeks.
By July 1944, however, a stalemate seemed to be setting in. The expansion of the bridgehead and Allied forces in Normandy was progressing much more slowly than anticipated, and despite Allied control of the air, enough high quality German forces were reaching the front to blunt various offensive drives by Allied ground forces.
The Allies, however, could replace their looses in a manner that the Germans could not. In the last week of July, American forces in the south were able to punch successfully through the German cordon while the majority of the German armoured forces were tied down fighting the British and Canadians further north. Hitler's insistence in early August 1944 on a full-scale counterattack rather than withdrawal to more defensible positions in response to this development led to the destruction of most what remained of the German armour and exposed the German forces in Normandy to possible envelopment between American forces swigging up from the south and British forces pushing southward. Hitler finally gave the order to retreat on 16th August, and though many Germans escaped from the Falaise pocket before it closed on 19th August, it was clear that German combat power had been destroyed. The Allies had won the battle for Normandy, another major landing on the French Riviera starting on 15th August had opened up a new and virtually unopposed front in the south, and the remnants of Army Group B were in headlong flight.
For a time it looked as if the war might end in 1944 as the US 3rd Army under General Patton as well as other Allied formations in the 12th and 21st Army Groups rapidly fanned out across France and Belgium, denying the enemy an opportunity to form a new defensive line of any substance. There were, however, limits to what could be accomplished. Allied logistical constraints, Anglo-American disagreement as to how to go about driving Germany, and the partial recovery of enemy strength combined to make a 1945 campaign necessary.
The central difficulty militating against an Allied offensive into Germany in the autumn of 1944 was the fact that the majority of supplies, not least fuel and ammunition, came by sea via a narrow funnel in Normandy and then all the way across France. Other than Cherbourg no major port in operational condition was in Allied hand by this point, transporting material across the beaches was lagued with difficulties, and the destruction of the railway network meant that the large (but by no means unlimited) Anglo-American truck fleet was largely responsible for transshipment. With limited available resources, serious Anglo-American friction arose over operational priorities. Montgomery (not the most tactful of British commanders) wanted American units to be placed under his command so that they could support a northern thrust though the Netherlands and down into the Ruhr valley by his 21st Army Group. Neither General Omar Bradly (commanding 12th Army Group) nor Patton (who wanted to push his 3rd US Army toward Frankfurt) liked this idea, and after much acrimony Eisenhower came down in favour of a broad-front advance once logistical constraints had been solved by the opening up of Marseilles and Antwerp to Allied shipping.
Eisenhower was probably right to be cautious about Montgomery's plan for a knockout blow before winter set in was demonstrated by the more limited operation that did allow to go forward in September 1944. Montgomery's plan was to try and outflank the prewar Siegfried Line and establish a bridgehead for further operations by using three airborne divisions (two American and one British) to seize bridges across Holland as far as the lower Rhine at Arnhem (Operation Market-Garden). The result was a disaster. German forces in the area were much stronger than anticipated, and British ground forces were unable to advance quickly enough to prevent airborne troops from being driven from the key bridge at Arnhem. The operation also diverted attention from the opening of the Scheldt Estuary and delayed the opening of Antwerp to shipping until November 1944.
A further and more alarming indication that the Wehrmacht still possessed much fighting power came in mid-December when Hitler, having marshaled his dwindling resources in men and material, launched a surprise offensive with twelve Panzer divisions in the thinly held Ardennes sector. The hope was to repeat the success of 1940 by driving towards Antwerp, cutting the northern Allied armies off from their supply base. Despite initial German success, however, the Allies recovered rapidly and managed to contain the enemy advance in what became known as the Battle of the Bulge. The Allied forces were mobile than the German army at this point and despite Anglo-American friction were able to rush units to critical points in time. Once the weather cleared on 23rd December 1944, Allied air superiority once more made itself felt. By Christmas Day the German advance, already in trouble, had ground to a halt. In January 1945 the remaining German units were withdrawn from the bulge.
Having built up his forces (the number of American troops in particular having increased significantly) and recovered from the Ardennes surprise, Eisenhower in the new year contemplated how best to invade the Reich, Montgomery, predictably, wanted all efforts to be subordinated to a thrust by his 21st Army Group. Equally predictably this was not an idea that won applause from American generals. Eisenhower decided in favour of a general advance to the Rhine, the establishment of bridgeheads, and then the envelopment of the Ruhr from north to south. A single massive thrust in the north could not be supported.
The Rhineland campaign ran from February through to the third week of March 1945, German units in the north putting up particularly strong opposition to the advance of the 2nd British, 1st Canadian, and 9th US armies. The result, however, was to put the Allies in a position to throw bridgeheads across the Rhine in the last fortnight of March (with the support of Bomber Command and airborne landings) and then place the 1st US Army and the 9th US Army in a position to surround what remained of German Army Group B in the Ruhr pocket (where over 300,00 soldiers surrendered in April).
Eisenhower, in March 1945, was more concerned with military than political considerations, which was why he saw a thrust southwestward, towards what was assumed to be the locale of a Nazi last stand in a redoubt amidst the Bavarian and Austrian Alps, rather than directly eastward towards Berlin, as the primary axis of advance. Allied movement eastward did still continue, however, the 2nd British army cleared the north German coast and the 9th and 1st US armies advanced toward the Elbe and Mulde rivers where they met up with the Soviet forces. organised German resistance in the West collapsed in the late April. The Nazi redoubt in the southeast proved to be a mirage, and it was the Red Army rather than the Allies who took Berlin at the end of the month. Political considerations urged on him by London and Washington did, however, move Eisenhower to focus on the British advance toward Lübeck in the north so as to secure the approaches to Denmark in the first days of May 1945 before the Soviets could get there. With nearly all Germany occupied and in ruins and surrounded, Hitler shot himself on 30th April, leaving the Berlin garrison commander to surrender on 2nd May. The German armies finally surrendered, a general Unconditional Surrender document being signed on 7th May 1945.