What was the outcome of the campaign of Normandy during World War 2?

The planners of Operation Overlord had established "phase lines" to mark the limits of where they projected the Allied forces would be at D+30, D+60, and D+90. They did not try to make projections for more than ninety days after the landings, realizing that events would dictate progress and any planning estimates would necessarily drift farther and farther from the reality.

But the Allies were not able to meet the projections of the planners. Hitler still maintained very strong forces north of the Seine River, convinced that the Normandy landings were a massive diversion, and that the real attack was yet to come in the Pas de Calais area. But practically all German forces south of the Seine were eventually drawn into the Normandy battle, bent on containing the beachhead. The result was that when the Allies finally cracked their way out through this tough crust of German defenders, there was nothing left with which to stop them going anywhere they pleased. There followed a very happy time for the Allies, and most of France was liberated by September, after the Allied breakout in late July. So though the Allies were initially unable to reach the phase line projected by the planners, by D+90 they were far beyond them.

The breakout of late July was called "The St. Lo breakout", as the Americans passed through that town on the way to open country. The attack was facilitated by a massive bombardment of the four-engine, heavy bombers of the 8th US Air Force. These were the airplanes ordinarily used in strategic bombing attacks deep into enemy territory, and the air commanders did not like to "waste" the days on which the weather allowed them to fly missions on such tactical raids. But the heavies pulverized the German front lines and the breakthrough was finally made, after about seven weeks of slogging through the hedgerows, liberating France one farm field at a time. Up to this time the Americans in the beachhead were all in the 1st Army, but the 3rd Army was activated around August 1, and Patton immediately was able to divide his army and send half of 3rd Army west to clear the Brittany peninsula, and the other half pivoted east and hooked around behind the Germans still confronting the British and Canadians at their end of the beachhead. Soon these Germans were three quarters surrounded and trapped in what came to be called "The Falaise Pocket", with only one road still open through Falaise over which the Germans could try to escape complete encirclement and capture. Allied fighter-bombers had a field day, and shot up all German traffic attempting to flee the pocket over several days. This original "Highway of Death" was littered end to end with wrecked, burnt out German tanks, trucks and half-tracks. Efforts to "close the pocket" and completely trap the Germans failed, and are still controversial to this day. Conservative Allied commanders feared to risk a collision between American and Canadian troops trying to meet on the battlefield coming toward one another to close the pocket, so the escape route remained open. But the Germans got away without their tanks and artillery.

The Germans had finally made an effort to make a serious, coordinated counter attack using several armored divisions, in an effort to wipe out the beachhead. But the pounding these units took from Allied tactical fighter bombers just trying to reach the battlefield was grueling, and delayed their attack until after the Americans had already broken out. This attack was never a terribly serious threat to wipe out the beachhead, but the US 30th Infantry Division is credited with "saving the breakout" by its epic stand at Mortain in early August against this counter attack.