This would be my first "What If" so if this has been covered then kindly let me know and point me towards its location so that I can read it. I have seen many comments as to "Thats just simply not possible", however in 1938, just a year before Germany invaded Poland the majority of the world said, "thats just not possible". If it's one thing that Germany proved throughout WW2 is that many things thought impossible are very much possible.

To fit this scenario it must be understood that one of the most damaging turn of events for Germany was the loss of the Luftwaffe through the Allies' constant use of upgraded planes such as the Mustang and Corsair, not to mention their long range bombers.

Scenario

Its 1936 and Hitler is planning his invasion of Europe. He knows that in his drive both East and West that eventually every major power will be involved in a truly global conflict. His hope is that his new Blitzkrieg will catch most countries off guard and allow him a swift victory. However the one truly unknown factor in his plan is the United States. If the US remains out of the fight then her economic might and nearly endless supply of men won't impact his plans. However he must plan in the event that the US enters the fray.

The Plan

While the world looks on from the sidelines at Spain's civil war Operation Irritus (Latin for "the void") is launched. Fearing the involvement of the US in his plans Hitler has commissioned an SS task force to infiltrate the United States along with equipment to wage a secret war against the US. Using civilian cargo ships the SS slowly brings in weapons to wage sabotage against the United States' industrial might.

When the US enters the war she immediately begins pumping out the vehicles of war that will fuel the fight in Europe. At this time Operation Irritus is in full swing with factories falling prey to sabotage, key personnel with companies such as North American Aviation would be assassinated and productions delayed if not totally stopping the release of the P51 Mustang, F4U Corsair, Sherman Tanks as well as ammunition and key materials. With their industry damaged and the fact that the US considered itself relatively safe the air superiority of the Luftwaffe remained in place allowing its ground forces to continue its fight with an umbrella of protection.

Conclusion

When the invasion of Normandy comes about the skies above France are filled with Stukas, 109s and the frightful new 262 Swallow.