During the Second World War, Operation Pointblank made the destruction of the Luftwaffe as a specific goal of the Allied strategic air campaign. The basic reason was that in 1940, and again in Africa the Luftwaffe had proven extremely effective in performing close air support in support of the German Army. Invading Europe was seen at best as an enormous challenge, one likely to fail if the Germans could contest the sky over beach site chosen. It was recognized early on that the Luftwaffe had to be defeated before an invasion of Europe could be successfully contemplated. This strategy had two basic components. First a bomber campaign to damage the German aircraft industry and the logistics system that supported it, such as starving the Luftwaffe of fuel so its pilots could not fly or train. Second, it was to force battle on the Germans, so that over time that force would be reduced by attrition. The two campaigns reinforced each other. After all, an enemy may not choose to give battle. By attacking the sinews of the German military, it was expected that the Germans would literally rise to the occasion so they could be shot down.
The general attitude of most airman going into World War II was the bomber will always get through. There was reason to believe this, as the attacker gets to choose when and where to attack. Radar was known to all sides, and being developed individually by all combatants, but it was brand new, and like any brand new system it took time and experinece to figure out how to best employ. An example of this is the detection of the Japanese Attack force approaching Pearl Harbor by an Army SCR-270 station that was discounted because very few had the experience to understand what they were actually seeing, and this two years into the war. Long range detection of aircraft had received a great deal of attention between the wars. Huge, concrete sonic reflectors still dot the English channel coast today that were built in the twenties and thirties to detect the engine noise of approaching aircraft engines. More mobile systems resembled oversized tubas, designed to amplify the distant noise and produce effective early warning. Some had directional horns that rested on a man's head and fed directly to his ears. None proved successful in wartime.
During the battles for Poland and France, the bomber, who was a tactical bomber supporting the Wehrmacht, got through. Radar was too new and the German decision cycle too fast for effective intervention. But once France had fallen and the RAF stood on the other side of the English Channel, things changed.
It is not often appreciated today that the British electronics industry in the late 1930s was very much at the standard of the world. The Daventry Experiment had proven that radio waves would in fact reflect off of aircraft. The British had been bombed by zeppelin during the First World War and that experience led the Royal Air Force to pay more attention to air defense than most competing forces. The head of Fighter Command, Sir Hugh Dowding, was a singular individual who saw immediately the potential of radar for air defence. He fought to develop what become the Chain Home radar stations that lined England's coast by 1940. The German Freya radar was in fact more advanced, but Dowding ran exercises that showed that data had to be combined and filtered, so that defending squadron leaders would not be overloaded with information, but rather told to go to a single place and time and altitude to meet the German bombers strength on strength. The creation of the Filter Room at RAF Bentley Priory was the key to the Dowding system that allowed 'the few' to defeat the Luftwaffe during the Battle of Britain.
One of those who believed the bomber would always get through was Hugh Trenchard, one of the founding father of the RAF. Sir Arthur Harris, (known as 'Bomber Harris') was a very strong follower of Trenchard's doctrine. However it was established early on that bombing by daylight, though it promised superior accuracy, that the bomber would not go through, or at least not enough of them returned home to make the effort worthwhile. Very quickly the RAF switched to night bombing and the English electronics industry did its part to make night bombing possible and at least accurate enough to hit a city. The Germans too had radar and quickly developed their own system and a technological race began as both sides worked to perfect and extend their operations at night.
The United States Army Air Force felt differently. The Boeing B-17 and Consolidated B-24 Liberator carried a lot more heavy machine guns than their British equivalents. Flying in a Combat Box formation it was believed the crossfire of multiple .50 caliber machine guns would kill so many fighters that the Bomber would also get through. This proved to be false. True, the B-17s did kill a lot of German fighters. But the German fighters killed a lot of B-17s, producing unsupportable attrition rates in 1942/1943.
Second, the Americans daylight bombing proved little better than the British in accuracy. Killing a factory requires hitting said factory many times. Machine tools are made of high quality materials and very robust. I once helped a friend move a drill press from the 1930s. It's a very nice piece and the sheer mass of it forced me to understand how machine tools could survive having a factory dropped around it. So when factories were hit, they were often back up and running within days. There was a general feeling early on that targeting the German ball bearing industry would create a bottleneck since such bearings were nigh ubiquitous in German aircraft engines. But the truth was the machines could be moved, and the lines repaired. Statistics show the Germans were able to increase aircraft engine production from 1939 until 1944, and general output of military goods. But it is dangerous to read too much into that. Increased does not mean production levels were achieved that would have happened in the absence of bombing. Time spent moving and repairing equipment is time that cannot be spent making aircraft engines or engine parts. A better measure is that the combined attacks of the RAF and the USAAC forced the Germans to give battle, so their fighter forces could be defeated.
Again, at first that was a problem. Superb a combat fighter as the Supermarine Spitfire was, neither it or the bf-109 was ever made into a long range fighter aircraft. The US was able to adapt its production lines more quickly and produce drop tanks that extended the range of its fighter aircraft. The Bristol Beaufighter and DeHavilland Mosquito were born with long range and accepted drop tanks. The merger of the Merlin engine and the Mustang airframe produced a sleek, maneuverable fighter that could get to Berlin and back.
This presented the Germans with an unsolvable problem. First of all, fighters used to defend Germany could not be used against Russia. Every fighter withdrawn for defense of the Reich wasn't there when needed at say, Stalingrad or Kursk. Bombers were big and tough, and generally took more damage than fighter aircraft. The original armament of German fighters was not adequate for shooting down B-17s. So they added more weapons, more cannon etc. Only cannon and ammunition are heavy and installing them created aerodynamic problems. An FW-190 configured for Defence of the Reich was a much easier target for the P-47 Thunderbolt pilots defending the bombers than the base model. But the factories mattered and the German people needed to know their cities were being defended. So the Luftwaffe gave battle. And the many superb pilots Germany had begun the war with died one by one in the skies over the Reich. After Big Week in February 1944 the Luftwaffe had been broken and Operation Pointblank a success. The Luftwaffe would not be able to truly contest the skies over France or Italy. Air Superiority had been achieved.
But one other thing deserves mention. War is about learning, and he who learns faster generally wins. Almost by accident, the Allies discovered the real Achilles heel of the Luftwaffe and German War machine overall: fuel. Fuel became critical when the Red Army began to really push back the Germans in 1943 who could have used the aircraft now defending the Reich. Synthetic fuel became critical, and fuel refineries and synthetic fuel plants proved a lot easier to put out of action by bombing than ball bearing factories. When D-Day came the Germans had few aircraft, few skilled pilots left and little fuel for them to use. The V weapons were terrifying, but militarily of little or no value.
When D-Day came and before, the Allies owned the skies. And a lot of that was because Operation Pointblank had done its job, to break the Luftwaffe as a fighting force. They broke it, and the Luftwaffe stayed broke.