When Germany learned of the Allied invasion at Normandy, it struggled to launch a real response. Bureaucratic nonsense, in-fighting, drinking and more created issues for the Germans. But even a perfectly-oiled machine would have struggled because the Allied air forces bombed the Nazis ahead of D-Day like I bombed tests in high school: repeatedly and overwhelmingly.
Allied war planners prepared for the massive bombing campaign for months, enacted it for over a year, and then watched it pay off in a single day and then for 11 months after.
The Limies and the Yanks find common ground
Great Britain's leaders breathed a sigh of relief when America, with a massive industrial base far out of range of Axis bombers, joined the war. But the leaders from across the pond found themselves at loggerheads often when it came to strategy and tactics.
One big sticking point came in the bombing plans: American leaders quickly adopted a strategy of daytime, precision bombing. They targeted critical bottlenecks in German wartime industries, like petroleum refining or fighter production, and then tightened the bottlenecks as much as possible. Britain, short equipment and skilled pilots after losses on the continent and in the Battle of Britain, favored nighttime raids that let them keep as many pilots while still inflicting some damage.
In late 1942 and early 1943, as the Allied powers started preparing for what would become D-Day and the invasion of Normandy, the fight over daytime or nighttime became more and more tense.
But then U.S. Army Gen. Ira C. Eaker wrote a memo to Prime Minister Winston Churchill. He ended it with, "If the RAF continues night bombing and we bomb by day, we shall bomb them round the clock and the devil shall get no rest." Churchill relented, and American and British planners started a joint bombing campaign under the Casablanca Directive of early 1943.
The full directive and other guidance from leadership made clear: The air forces were not to win the war. They were to prepare the continent for a combined arms invasion. Other, lesser priorities made it into the directive, like supporting operations in the Mediterranean, but the directive ordered that, until it was rescinded, the priority was to go to preparations for an invasion of the European continent.
And Oh My God, did the Allied air forces work to break Germany's ability to fight. The Air Force gets little credit for D-Day, but that's because it put in the work for a year beforehand.
While British bombers struck entire industrial areas at night, American bombers assaulted key industries, roads, rails, and enemy units.
The Yanks pummeled aircraft factories to reduce Luftwaffe units and brought fighters along to kill German pilots during the raids. The broad scope of operations was to destroy ball bearings, petroleum, grinding wheels, abrasives, metal production, rubber, and logistics.
Americans hit petroleum refining so hard that Luftwaffe officer Albert Speer later claimed he told Hitler, "It would be pointless to have tanks if we could not produce enough fuel."
While the British forces had found great success bombing railroad junctions in Italy, they upped the ante in Germany. They developed special bombs for destroying submarine pens and collapsing mountain tunnels.
The final push by the air forces before D-Day
The joint, constant bombing operations started in 1943. But in January 1944, both air forces dug deep to prepare for a summer invasion. They intensified attacks on infrastructure and launched Operation Argument, a week-long assault on Luftwaffe production.
By the time June 1944 marched around, German defenders could no longer rely on air cover, on submarine support, or on steady reinforcements and resupply. Germany had so few transportation vehicles that many Normandy defenders were in static units that could not transport themselves.
On D-Day, American bombers assaulted German positions near the coast with little fear of fighter intercepts, though some attacks happened. Heavy ground defenses took a large toll on Allied air forces and on the paratroopers who jumped that day.